[Federal Register Volume 59, Number 159 (Thursday, August 18, 1994)]
[Unknown Section]
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From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-20042]
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[Federal Register: August 18, 1994]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 58
[FRL-4842-4]
Ambient Air Quality Surveillance Siting Criteria for Open Path
Analyzers
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The EPA proposes to amend provisions of part 58 of chapter I
of title 40 of the Code of Federal Regulations to define the
appropriate ambient air monitoring criteria for open path (long-path)
analyzers. The proposed revisions to the Ambient Air Quality
Surveillance regulations would define the siting requirements for open
path analyzers used as State and Local Air Monitoring Stations (SLAMS),
which includes both National Air Monitoring Stations (NAMS) and
Photochemical Assessment Monitoring Stations (PAMS), as well as the
quality assurance procedures for this technology. These changes will
allow the ambient air monitoring community to effectively use open path
monitoring data for regulatory purposes.
DATES: Comments must be received on or before September 19, 1994.
Requests for public hearing must be received by September 2, 1994. If a
hearing is held, comments must be received on or before 30 days from
the conclusion of the hearing.
ADDRESSES: Comments should be submitted (in duplicate, if possible) to:
Air Docket (LE-131), Attention: Docket Number A-93-44, U.S.
Environmental Protection Agency, room M-1500, 401 M Street, SW.,
Washington, DC 20460.
Public hearing: A public hearing will be held, if requested, in
accordance with information provided in the DATES section of this
proposal, to provide interested parties an opportunity for oral
presentation of data, views, or arguments concerning the proposed
revisions. If anyone contacts EPA requesting a public hearing, it will
be held at the EPA's Environmental Research Center, Research Triangle
Park, North Carolina. Persons interested in attending the hearing or
wishing to present oral testimony should notify Ms. Lee Ann B. Byrd,
Monitoring and Reports Branch (MD-14), U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina 27711, telephone number
(919) 541- 5367. Specific dates and other pertinent details of this
public hearing will be published in a separate Federal Register notice.
Docket: Docket Number A-93-44, containing supporting information
used in developing these revised regulations, is available for public
inspection and copying between 8:30 a.m. and 12 noon, and between 1:30
p.m. and 3:30 p.m., Monday through Friday, at EPA's Air Docket Section
at the address noted above. As provided in 40 CFR Part 2, a reasonable
fee may be charged for copying.
FOR FURTHER INFORMATION CONTACT: Ms. Lee Ann B. Byrd at telephone (919)
541-5367 concerning this action. The address is Monitoring and Reports
Branch (MD-14), U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina 27711.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Authority
II. Background of Proposed Rule
III. Discussion of Proposed Revisions to Regulation
A. Section 58.1 Definitions
B. Appendix A--Quality Assurance Requirements for State and
Local Air Monitoring Stations (SLAMS)
C. Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
D. Appendix E--Probe and Path Siting Criteria for Ambient Air
Quality Monitoring
IV. Comments and the Public Docket
V. Administrative Requirements
A. Administrative Designation.
B. Reporting and Recordkeeping Requirements
C. Regulatory Flexibility Act
I. Authority
Authority: sections 110, 301(a), 313, and 319 of the Clean Air
Act as amended 42 U.S.C. 7410, 7601(a), 7613, 7619.
II. Background of Proposed Rule
The Clean Air Act, as amended in 1990, requires, in sections
181(b)(2), 185A, and 186(b)(2)(A), ambient air quality monitoring for
purposes of defining areas of nonattainment with the National Ambient
Air Quality Standards (NAAQS), evaluating progress toward achievement
of the NAAQS pursuant to State implementation plans (SIP's), and
reporting air quality data to the EPA to document the status and trends
of the Nation's air quality. These are nontrivial activities, and to
achieve the aforementioned objectives, the EPA must ensure that the
ambient air monitoring networks consist of high quality instruments
that produce accurate concentration measurements. As new monitoring
techniques are developed, the EPA evaluates the new methodology and, as
appropriate, determines how to effectively incorporate it into the
existing air quality monitoring program. To assess new ambient air
monitoring instruments for those pollutants with established NAAQS, the
EPA currently uses the Ambient Air Monitoring Reference and Equivalent
Method regulatory procedures detailed in title 40, chapter 1, part 53.
The EPA does not formally regulate the performance testing of ambient
air monitoring instruments, which measure pollutants without
established NAAQS. Methodology for collected ozone (O3) precursor
data (specified in the Photochemical Assessment Monitoring program as
volatile organic compounds and oxides of nitrogen) is reviewed in the
``Technical Assistance Document for Sampling and Analysis of Ozone
Precursors,'' and any subsequent revisions, EPA/600-8-91/215, October
1991. Supplementing the part 53 performance requirements and the
aforementioned ``Technical Assistance Document,'' the part 58 Ambient
Air Quality Surveillance regulation specifies how to most appropriately
conduct routine ambient air monitoring through pollutant-specific
monitor siting criteria, operation schedules, monitoring network
design, and data reporting. Under the part 58 provisions, each SLAMS
must employ reference or equivalent methods, as determined according to
part 53, and meet all applicable siting requirements as contained in
part 58, before its data can be used for regulatory purposes.
Specifically, these regulatory actions include comparison with the
NAAQS and other SIP-related activities. It is important to note that
the NAMS and the PAMS are subsets of the SLAMS networks; therefore,
provisions for the SLAMS also apply to both the NAMS and PAMS, as
included in this proposal.
A new technique for monitoring pollutants in ambient air has been
developed and introduced to the EPA. Instruments based on this new
technique, called open path (or long-path) analyzers, use ultraviolet,
visible, or infrared light to measure nitrogen dioxide (NO2),
O3, carbon monoxide (CO), sulfur dioxide (SO2), and other
gaseous pollutant concentrations over a path of several meters up to
several kilometers. The concentration measurements obtained by these
open path analyzers are path-integrated, or path-averaged, values.
Traditional fixed point analyzers measure pollutant concentrations at
one specific point by extracting an air sample from the atmosphere
through an inlet probe. A list of all EPA-approved reference and
equivalent ambient air monitoring methods is available through the
docket. Due to the fundamental difference in the measurement principles
of open path and point analyzers, there may be trade-offs in using each
type of instrument for certain applications. Because of the ability of
open path analyzers to measure pollutant concentrations over a path,
these new techniques are expected to provide better spatial coverage,
and thereby a better assessment of a general population's exposure to
air pollutants for certain applications. However, due to this same
path-averaging characteristic, open path analyzers could underestimate
high pollutant concentrations at specific points within the measurement
path for other ambient air monitoring situations. The applicability of
either technique to a particular monitoring scenario is dependent on a
number of factors including plume dispersion characteristics,
monitoring location, pollutant of interest, population density, site
topography, and monitoring objective. The EPA has considered these
factors in evaluating the advantages and disadvantages of using open
path analyzers for the various ambient air monitoring applications
detailed in 40 CFR part 58. Additionally, several studies of the
comparability of data collected with point and open path analyzers have
been conducted by the EPA and by other organizations. The most recent
EPA study of these two methodologies was completed during the summer of
1993 in Baytown, Texas. Results from this study and others are
available in the docket for public review. The EPA solicits comment on
these studies and on the comparability of using path-averaged and point
measurements in the Nation's ambient air monitoring programs.
The EPA is currently assessing the performance of an open path
analyzer as a candidate method under part 53 to determine if it should
be designated as an equivalent method for one or more of those
pollutants. In parallel with this effort, the EPA has developed the
appropriate part 58 siting and quality assurance criteria for open path
analyzers, which are contained in this proposal.
The existing part 58 monitoring network design criteria define the
monitoring objectives for a particular site in terms of measurement
scale. More specifically, each ambient air monitoring station is
located in such a way that it represents a particular air parcel or
volume. The regulation uses six measurement scales to describe the size
of these air parcels. These six scales are: microscale (dimensions of
several meters to approximately 100 meters), middle scale (100 to 500
meters), neighborhood scale (500 meters to 4 kilometers), urban scale
(4 to 50 kilometers), regional scale (tens to hundreds of kilometers),
and national or global scales. (National and global scales are
generally not applicable for a single air monitoring station. National
and global averages are more appropriately determined by networks of
various monitoring stations.) Within each of these measurement scales,
it is assumed that the pollutant concentrations are relatively
homogeneous; therefore, a monitor placed at any point in the area,
within the tolerances of this siting regulation, measures a
concentration representative of that area.
Depending on the objective for a particular SLAMS, each pollutant
can be monitored on a particular measurement scale as defined in Table
5 of appendix D in part 58. The applicability of the first five scales
to monitoring the four pollutants referenced in this proposal, CO,
NO2, O3, and SO2, follows:
Summary of Spatial Scales for Selected SLAMS
------------------------------------------------------------------------
Ozone
Measurement Scale CO NO2 O3 SO2 precursors\1\
------------------------------------------------------------------------
Micro-....................... Yes.. No... No... No... No.
scale........................
Middle scale................. Yes.. Yes.. Yes.. Yes.. No.
Neighborhood scale........... Yes.. Yes.. Yes.. Yes.. Yes.
Urban scale.................. No... Yes.. Yes.. Yes.. Yes.
Regional..................... No... No... Yes.. Yes.. No.
------------------------------------------------------------------------
\1\Ozone precursors, as defined in the PAMS program, include volatile
organic compounds, oxides of nitrogen, and selected carbonyls.
Existing regulations in part 58 state that the pollutant
concentration within a particular measurement scale is nearly
homogeneous, and that a point measurement collected in this same scale
generally represents any other point within that scale. This basic
provision defines how ambient air monitoring data can be used to
represent the air quality in a neighborhood, city, or other geographic
region. Based on these current provisions, it is reasonable to accept
that a path-averaged measurement taken within the dimensions and other
siting specifications of that measurement scale would provide a value
descriptive of that same geographic region. In order to maintain data
comparability between open path and point analyzers, the revisions
contained in this proposal are based on the siting criteria currently
being used with conventional fixed point ambient air monitoring
networks. The most obvious difference between the proposed and existing
siting criteria is that the new requirements are defined in terms of a
``probe'' (applicable to point analyzers), a ``monitoring path''
(applicable to open path analyzers), or both. Some minor flexibility in
siting criteria was added for open path analyzers to compensate for the
additional difficulties in locating suitable sites for the various
equipment used with an open path analyzer, such as retroreflectors,
receivers, and transmitters. Nonetheless, these criteria should still
provide a concentration representative of the area to be monitored.
It is important to note that criteria for open path measurement of
CO in a street canyon scenario, typically defined in terms of
microscale dimensions (up to 100 meters), is not included in this
proposal. The siting criteria currently used for microscale CO
monitoring is unique and narrow in scope in comparison to other
monitoring scenarios. Adapting the existing siting criteria to
accommodate path measurement techniques, as this proposal does for
other types of monitoring scales, would unduly restrict the usage of
open path analyzers for this particular application. In order to fully
address more appropriate siting criteria for microscale CO monitoring
using open path analyzers, the EPA must more fully evaluate the effects
of measuring path-averaged CO concentrations across roadways,
intersections, and at locations other than those currently defined in
the part 58 regulation. The EPA specifically solicits comments from the
public regarding the use of open path analyzers for measuring CO in
microscale applications.
III. Discussion of Proposed Revisions to Regulations
A. Section 58.1 Definitions
Today's proposal would amend the definitions section of part 58 by
adding several new definitions that are necessary to clearly define the
proposed new requirements for open path analyzers. Definitions for
``point analyzer'' and ``open path analyzer'' would be added to define
these two types of automated instruments and to clarify the distinction
between them, since the various new and existing requirements may apply
to one or the other or both types of analyzers. A new definition for
``probe'' is proposed to specify the inlet where an air sample is
extracted from the atmosphere for delivery to a sampler or point
analyzer. This definition would clarify that location requirements
applicable to point analyzers apply to the analyzer's probe and not to
the analyzer (or sampler) itself, which could be located some distance
from the probe. Similarly, a new definition is proposed for
``monitoring path'' to describe the path in the atmosphere over which
an open path analyzer measures and averages a pollutant concentration.
Closely associated with the term ``monitoring path'' are new
definitions for ``monitoring path length,'' to describe the scalar
length of the monitoring path, and ``optical measurement path length,''
to describe the actual length of the optical beam of an open path
instrument. The length of the optical beam may be two or more times the
length of the monitoring path when one or more mirrors are used to
cause the optical beam to pass through the monitoring path more than
once.
To help describe the new requirements for data quality assessment
procedures, the term ``effective concentration'' is proposed. It would
refer to the ambient concentration of a pollutant over the monitoring
path that would be equivalent to a much higher concentration of the
pollutant contained in a short calibration cell inserted into the
optical beam of an open path analyzer during a precision test or
accuracy audit. Specifically, effective concentration is proposed to be
defined as the actual concentration of the pollutant in the test cell
multiplied by the ratio of the optical measurement path length of the
test cell to the optical measurement path length of the atmospheric
monitoring path. Also, when a calibration cell is inserted into the
actual atmospheric measurement beam of an open path analyzer for a
precision or accuracy test, the resulting measurement reading would be
the sum of the pollutant concentration in the calibration cell and the
pollutant concentration in the atmosphere. The atmospheric pollutant
concentration must be measured separately and subtracted from the test
measurement to produce a ``corrected concentration,'' which would be
the true test result. Thus, the term ``corrected concentration'' is
proposed to define the result of such a precision or accuracy
assessment test after correction of the test measurement by subtracting
the atmospheric pollutant concentration.
Finally, a formal definition of ``monitor'' is proposed to clarify
its use in the regulations as a generic term to refer to any type of
ambient air analyzer or sampler that is acceptable for use in a SLAMS
monitoring network under Appendix C of this part. A monitor could thus
be a point analyzer, an open path analyzer, or a sampler.
B. Appendix A--Quality Assurance Requirements for State and Local Air
Monitoring Stations (SLAMS)
Appendix A sets forth both general quality assurance requirements
applicable to SLAMS air monitoring as well as specific procedures for
assessing the quality of the monitoring data obtained in SLAMS
monitoring networks. While the general quality assurance requirements
(in section 2) would be directly applicable to open path analyzers
without change, the more specific data quality assessment procedures
(in section 3) must be modified somewhat to apply to open path
analyzers. Accordingly, changes to these procedures are proposed to
incorporate appropriate data quality assessment tests applicable to
open path monitoring instruments. To the extent possible, the new
requirements are similar or parallel to the existing requirements for
point analyzers.
For both the precision test (Sec. 3.1) and the accuracy audit
(Sec. 3.2), the proposed new requirements specify that an optical
calibration or test cell containing a pollutant concentration standard
must be inserted into the optical measurement beam of the open path
analyzer. Both theory and testing indicate that the use of such a
calibration or test cell is equivalent in accuracy to measurement of
the equivalent pollutant concentration in air over the entire
monitoring path of an open path analyzer. Each concentration standard
must be selected such that it produces an ``effective concentration''
equivalent to a specified ambient concentration over the monitoring
path. As noted previously, effective concentration is defined as the
actual concentration of the pollutant in the test cell multiplied by
the ratio of the optical measurement path length of the test cell to
the optical measurement path length of the atmospheric monitoring path.
The effective concentrations specified for the precision and accuracy
tests for open path analyzers would be the same as the test
concentrations currently specified in these procedures for point
analyzers.
Ideally, precision and accuracy assessments should test a
monitoring instrument in its normal monitoring configuration.
Therefore, the proposed test procedures require that the test or
calibration cell containing the test pollutant concentration standard
be inserted into the actual atmospheric measurement beam of the open
path analyzer. The resulting test measurement of the pollutant
concentration would thus be the sum of the test concentration in the
cell and the pollutant concentration in the atmosphere, because the
measurement beam would pass through both the test cell and the
atmospheric monitoring path. Accordingly, a correction for the
atmospheric concentration is required to obtain the true test result.
In the proposed procedures, the atmospheric pollutant concentration
would be measured immediately before and again immediately after the
precision or accuracy test, and the average of these two measurements
would be subtracted from the test concentration measurement to produce
a ``corrected concentration,'' which would be reported as the test
result.
The corrected concentration reported for a precision or accuracy
test may not be accurate if the atmospheric pollutant concentration
changes during the test. When the ambient concentration is variable,
the average of the pre- and post-test measurements may not be an
accurate representation of the ambient pollutant concentration during
the test. The proposed test procedures recommend that these tests
should be carried out, if possible, during periods when the atmospheric
pollutant concentration is low and steady. The lower the atmospheric
pollutant concentration, the steadier the concentration is likely to be
and the better the pre- and post-test measurements will represent the
actual atmospheric concentration during the test measurement. Further,
the procedures propose that if the pre- and post-test measurements of
the atmospheric concentration differ by more that 20 percent of the
effective concentration of the test standard, the test result would be
discarded and the test repeated.
It is recognized that the proposed tests for precision and accuracy
for open path analyzers, as well as the existing tests for point
analyzers, are described in very general terms, and that additional,
more detailed information and guidance is usually necessary for an
analyzer operator to carry out these tests properly. Accordingly,
section 3 of appendix A is proposed to be amended by adding an explicit
indication that supplemental information and guidance to assist the
analyst in conducting these tests may be available in the publication,
``Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume II'' (EPA-600/4-77-027a, identified as Reference 3 at the end of
Appendix A), or in the operation or instruction manual associated with
the particular monitor being used.
The proposed techniques for precision and accuracy assessment of
open path analyzers are based largely on consultations with the
manufacturer, along with EPA tests, of the differential optical
absorption spectrometer that is currently under consideration by EPA
for possible designation as equivalent methods under 40 CFR part 53.
However, it is desirable that the techniques be generic in nature, if
possible, so that they would be applicable to other types of open path
monitoring instruments as well. In addition, for some types of open
path instruments or for some installations or configurations, there may
be technical reasons why the proposed techniques for precision and
accuracy assessment may not be feasible, appropriate, or advisable. The
procedures, as currently proposed, allow for the use of an alternate
local light source or an alternate optical path that does not include
the normal atmospheric monitoring path, if such alternate configuration
is permitted by the operation or instruction manual associated with the
analyzer. Since the analyzer operation or instruction manual would be
subject to approval as part of the requirements for EPA designation of
an open path analyzer as an equivalent method, EPA would thereby have
control over the alternate configurations that would be allowable for
the precision and accuracy assessment tests.
In view of these issues regarding the precision and accuracy
assessment techniques, EPA specifically solicits comments on: (1) The
suitability of the proposed techniques; (2) the advisability of a
technique that requires correction of the test result for the
atmospheric pollutant concentration versus a technique that does not
require that correction but does not test the normal atmospheric
measurement components and configuration; (3) the proposed technique
for correcting test measurements for the atmospheric pollutant
concentration, if required, and the 20 percent limit on the difference
between the pre- and post-test measurements of the atmospheric
concentration; and (4) whether the proposed techniques are sufficiently
generic in nature to apply to various other types of open path
analyzers that might be applicable to SLAMS monitoring, or how the
techniques could be made more generic.
C. Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
Appendix B sets forth both general quality assurance requirements
for PSD monitoring as well as specific procedures for assessing the
quality of the monitoring data obtained in PSD monitoring networks. The
amendments and procedures proposed for Appendix B to extend the
existing requirements to open path analyzers are essentially identical
to the changes proposed for Appendix A.
D. Appendix E--Probe and Path Siting Criteria for Ambient Air Quality
Monitoring
This proposal would amend Appendix E by adding new siting criteria
applicable to open path analyzers for monitoring of SO2, O3,
NO2, CO, and O3 precursors (defined in the PAMS program as
volatile organic compounds, oxides of nitrogen, and selected
carbonyls). Because of the substantial similarity in the siting
criteria for SO2, O3, and NO2 (both the existing
criteria for point monitors and proposed new criteria for open path
analyzers), the siting requirements for these three pollutants are
proposed to be combined, consolidated, and set forth in section 2 of
appendix E. The existing criteria for SO2, O3, and NO2
in sections 3, 5, and 6 would be deleted, and those sections would be
reserved. As noted below, the criteria for CO monitoring are somewhat
different, so they would be retained in a separate section 4. Siting
criteria for measuring O3 and its precursors as part of a PAMS
network are included in section 10. In all cases, the new open path
provisions would be incorporated into the existing provisions, as
appropriate.
The proposed new open path siting requirements largely parallel the
existing requirements for point analyzers, with the revised provisions
applicable to either a ``probe'' (for point analyzers), a ``monitoring
path'' (for open path analyzers), or both, as appropriate. Accordingly,
criteria for the monitoring path of an open path analyzer are proposed
for horizontal and vertical placement, spacing from minor sources,
spacing from obstructions, spacing from trees, and spacing from
roadways. The open path requirements would apply to most of the
monitoring path--generally 80 or 90 percent--but not to the entire
monitoring path, to allow some needed flexibility in siting open path
analyzers. For example, using the proposed 80 percent requirement, a
monitoring path may be sited across uneven terrain, where up to 20
percent of the monitoring path may not fall within the proposed 3 to 15
meter specification for height above ground.
In addition to the criteria common to both point and open path
analyzers mentioned above, two new provisions, applicable only to open
path analyzers, would limit the maximum length of the monitoring path
and the cumulative interferences on the path. The maximum monitoring
path length limit would help to ensure that open path monitoring data
represent the air volume that they are intended to measure according to
the monitoring objectives of the spatial scale identified for the site.
Similarly, the limit for the cumulative interferences on the monitoring
path would control the total amount of interferences from minor
sources, roadways, obstructions, and other factors that might unduly
influence the monitoring data collected by an open path analyzer. This
limit is necessary because a long monitoring path presents a much
greater opportunity to be affected by multiple interferences. It is
also recognized that State or local air monitoring agencies may
encounter difficulties in locating atmospheric monitoring equipment due
to vandalism, scarcity of available sites, and other considerations;
therefore, certain provisions are included in both the existing and the
proposed new provisions of the regulation to accommodate these
difficulties.
In the consolidation of current sections 3, 5, and 6 to section 2,
Tables 2 and 3, which list the minimum separation distance between
O3 and NO2 stations and nearby roadways, would be combined
and redesignated as Table 1. As a result, Table 1 (in section 3), Table
4 (in section 7), Table 5 (in section 10), and Table 6 (in section 12)
would be renumbered as tables 2, 3, 4, and 5, respectively. Finally,
the summary of all the general siting requirements in renumbered Table
5 would be modified to include the new criteria for monitoring paths.
IV. Comments and the Public Docket
The EPA welcomes comments on all aspects of this proposed
rulemaking, specifically: (a) The appropriateness of using open path
(long-path) analyzers to measure CO, O3, SO2, NO2, and/
or O3 precursors (defined in the PAMS program as volatile organic
compounds, oxides of nitrogen, and selected carbonyls); (b) the ability
of a monitoring agency to use an open path analyzer in a manner
consistent with these siting criteria; (c) using open path analyzers to
measure CO in microscale scenarios; (d) the precision and accuracy
assessment techniques as described in the proposed Appendix A and
Appendix B regulations; (e) using open path analyzers to measure
SO2 in source-oriented ambient air monitoring networks,
particularly in micro- and middle-scale applications; and (f) all
available and relevant study information on the comparability of open
path and point ambient air monitoring. All comments, with the exception
of proprietary information, should be directed to the EPA Air Docket
Section, Docket No. A-93-44.
Those who wish to submit proprietary information for consideration
should clearly separate such information from other comments by:
Labeling proprietary information ``Confidential Business
Information,'' and;
Sending proprietary information directly to the contact
person listed (see FOR FURTHER INFORMATION CONTACT) and not to the
public docket.
This will help ensure that proprietary information is not
inadvertently placed in the docket. If a commenter wants the EPA to use
a submission labeled as confidential business information as part of
the basis for the final rule, then a nonconfidential version of the
document, which summarizes the key data or information, should be sent
to the docket.
Information covered by a claim of confidentiality will be disclosed
by the EPA only to the extent allowed and by the procedures set forth
in 40 CFR part 2. If no claim of confidentiality accompanies the
submission when it is received by the EPA, the submission may be made
available to the public without notifying the commenters.
V. Administrative Requirements
A. Administrative Designation
Executive Order 12866
Under Executive Order 12866 (58 FR 51735 (October 4, 1993)) the
Agency must determine whether the regulatory action is ``significant''
and therefore subject to Office of Management and Budget (OMB) review
and the requirements of the Executive Order. The Order defines
``significant regulatory action'' as one that is likely to result in a
rule that may:
(1) Have an annual effect on the economy of $100 million or more or
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, or tribal governments or
communities;
(2) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another Agency;
(3) Materially alter the budgetary impact of entitlements, grants,
user fees, or loan programs or the rights and obligations or recipients
thereof; or
(4) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
It has been determined that this rule is not a ``significant
regulatory action'' under the terms of Executive Order 12866 and is
therefore not subject to OMB review.
B. Reporting and Recordkeeping Requirements
All of the information collection requirements contained in part 58
have been approved by the OMB under the Paperwork Reduction Act of
1980, 44 U.S.C. 3501 et seq., and have been assigned OMB Control Number
2060-0084. This proposed amendment to Part 58 does not add any new
information collection requirements.
C. Regulatory Flexibility Act
Pursuant to section 605(b) of the Regulatory Flexibility Act, 5
U.S.C. 605(b), the Administrator certifies that this rule will not have
a significant economic impact on a substantial number of small
entities. This rulemaking package does not impose any additional
requirements on small entities, rather, it is this proposal's intent to
provide all entities with the option to choose the most suitable
ambient air method for their particular application. This proposal
provides the appropriate siting and quality assurance criteria for a
new ambient air monitoring technology (open path analyzers) as they are
used in various applications. All of the criteria listed in this
rulemaking package parallel existing requirements and vary only as
necessary due to technological differences between measurement
techniques. It is possible that a beneficial impact may be encountered
by some small entities that use this new technology in certain
scenarios.
List of Subjects in 40 CFR Part 58
Air pollution control, Ambient air monitoring, Ambient air
monitoring networks and siting criteria, Intergovernmental relations,
National ambient air monitoring program, Quality assurance
requirements, Reporting and recordkeeping requirements, State and local
agency ambient air monitoring programs.
Dated: August 4, 1994.
Carol M. Browner,
Administrator.
For reasons set forth in the preamble, title 40, chapter I, part 58
of the Code of Federal Regulations is proposed to be amended as
follows:
PART 58--[AMENDED]
1. The authority citation for part 58 continues to read as follows:
Authority: 42 U.S.C. 7410, 7601(a), 7613, and 7619.
2. In Sec. 58.1, the following definitions are added:
Sec. 58.1 Definitions.
* * * * *
(z) Point analyzer is an automated analytical method that measures
pollutant concentration in an ambient air sample extracted from the
atmosphere at a specific inlet probe point and that has been designated
as a reference or equivalent method in accordance with part 53 of this
chapter.
(aa) Probe is the actual inlet where an air sample is extracted
from the atmosphere for delivery to a sampler or point analyzer for
pollutant analysis.
(bb) Open path analyzer is an automated analytical method that
measures the average atmospheric pollutant concentration in situ along
one or more monitoring paths having a monitoring path length of 5
meters or more and that has been designated as a reference or
equivalent method under the provisions of part 53 of this chapter.
(cc) Monitoring path for an open path analyzer is the actual path
in space over which the pollutant concentration is measured and
averaged.
(dd) Monitoring path length of an open path analyzer is the length
of the monitoring path in the atmosphere over which the average
pollutant concentration measurement is determined. See also, ``optical
measurement path length.''
(ee) Optical measurement path length is the actual length of the
optical beam over which measurement of the pollutant is determined.
Generally, the optical measurement path length is:
(1) Equal to the monitoring path length for a (bistatic) system
having transmitter and receiver at opposite ends of the monitoring
path;
(2) Equal to twice the monitoring path length for a (monostatic)
system having a transmitter and receiver at one end of the monitoring
path and a mirror or retroreflector at the other end; or
(3) Equal to some multiple of the monitoring path length for more
complex systems having multiple passes of the measurement beam through
the monitoring path.
(ff) Effective concentration pertains to testing an open path
analyzer with a high-concentration calibration or audit standard gas
contained in a short test cell inserted into the optical measurement
beam of the instrument. Effective concentration is the equivalent
ambient-level concentration that would produce the same spectral
absorbance over the actual atmospheric monitoring path length as
produced by the high-concentration gas in the short test cell.
Quantitatively, effective concentration is equal to the actual
concentration of the gas standard in the test cell multiplied by the
ratio of the path length of the test cell to the actual atmospheric
monitoring path length.
(gg) Corrected concentration pertains to the result of an accuracy
or precision assessment test of an open path analyzer in which a high-
concentration test or audit standard gas contained in a short test cell
is inserted into the optical measurement beam of the instrument. When
the pollutant concentration measured by the analyzer in such a test
includes both the pollutant concentration in the test cell and the
concentration in the atmosphere, the atmospheric pollutant
concentration must be subtracted from the test measurement to obtain
the corrected concentration test result. The corrected concentration is
equal to the measured concentration minus the average of the
atmospheric pollutant concentrations measured (without the test cell)
immediately before and immediately after the test.
(hh) Monitor is a generic term for an instrument, sampler,
analyzer, or other device that measures or assists in the measurement
of atmospheric air pollutants and is acceptable for use in ambient air
surveillance under the provisions of appendix C to this part, including
both point and open path analyzers that have been designated as
reference or equivalent methods under part 53 of this chapter and air
samplers that are specified as part of a manual method that has been
designated as a reference or equivalent method under part 53 of this
chapter.
Appendix A [Amended]
3. Appendix A is amended as follows:
a. The fourth paragraph of section 3 introductory text is revised.
b. Section 3.1 is revised.
c. The text preceding the table in the second paragraph, and the
seventh, and eighth paragraphs of Sec. 3.2 are revised; and a new
paragraph is added between the seventh and eighth paragraphs.
d. Table A-1 is revised.
Appendix A--Quality Assurance Requirements for State and Local Air
Monitoring Stations (SLAMS)
* * * * *
3. Data Quality Assessment Requirements
* * * * *
Assessment results shall be reported as specified in section 4.
Concentration and flow standards must be as specified in Secs. 2.3
or 3.4. In addition, working standards and equipment used for
accuracy audits must not be the same standards and equipment used
for routine calibration. Additional information and guidance in the
technical aspects of conducting these tests may be found in
Reference 3 or in the operation or instruction manual associated
with the analyzer or sampler. Concentration measurements reported
from analyzers or analytical systems (indicated concentrations)
should be based on stable readings and must be derived by means of
the same calibration curve and data processing system used to obtain
the routine air monitoring data (see Reference 1 and Reference 3,
section 2.0.9.1.3(d)). Table A-1 provides a summary of the minimum
data quality assessment requirements, which are described in more
detail in the following sections.
3.1 Precision of Automated Methods
A one-point precision check must be carried out at least once every
2 weeks on each automated analyzer used to measure SO2, NO2,
O3, and CO. The precision check is made by challenging the
analyzer with a precision check gas of known concentration (effective
concentration for open path analyzers) between 0.08 and 0.10 ppm for
SO2, NO2, and O3 analyzers, and between 8 and 10 ppm for
CO analyzers. To check the precision of SLAMS analyzers operating on
ranges higher than 0 to 1.0 ppm SO2, NO2, and O3, or 0
to 100 ppm for CO, use precision check gases of appropriately higher
concentration as approved by the appropriate Regional Administrator or
the Regional Administrator's designee. However, the results of
precision checks at concentration levels other than those specified
above need not be reported to the EPA. The standards from which
precision check test concentrations are obtained must meet the
specifications of Sec. 2.3.
Except for certain CO analyzers described below, point analyzers
must operate in their normal sampling mode during the precision
check, and the test atmosphere must pass through all filters,
scrubbers, conditioners, and other components used during normal
ambient sampling and as much of the ambient air inlet system as is
practicable. If permitted by the associated operation or instruction
manual, a CO point analyzer may be temporarily modified during the
precision check to reduce vent or purge flows, or the test
atmosphere may enter the analyzer at a point other than the normal
sample inlet, provided that the analyzer's response is not likely to
be altered by these deviations from the normal operational mode.
If a precision check is made in conjunction with a zero or span
adjustment, it must be made prior to such zero or span adjustments.
Randomization of the precision check with respect to time of day,
day of week, and routine service and adjustments is encouraged where
possible.
Open path analyzers are tested by inserting a test cell
containing a precision check gas concentration into the optical
measurement beam of the instrument. If possible, the normally used
transmitter, receiver, and, as appropriate, reflecting devices
should be used during the test, and the normal monitoring
configuration of the instrument should be altered as little as
possible to accommodate the test cell for the test. However, if
permitted by the associated operation or instruction manual, an
alternate local light source or an alternate optical path that does
not include the normal atmospheric monitoring path may be used. The
actual concentration of the precision check gas in the test cell
must be selected to produce an ``effective concentration'' in the
range specified above. Generally, the precision test concentration
measurement will be the sum of the atmospheric pollutant
concentration and the precision test concentration. If so, the
result must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentrations measured
by the instrument immediately before and immediately after the
precision check test from the precision test concentration
measurement. If the difference between these before and after
measurements is greater than 20 percent of the effective
concentration of the test gas, discard the test result and repeat
the test. If possible, open path analyzers should be tested during
periods when the atmospheric pollutant concentrations are relatively
low and steady.
Report the actual concentration (effective concentration for
open path analyzers) of the precision check gas and the
corresponding concentration measurement (corrected concentration, if
applicable, for open path analyzers) indicated by the analyzer. The
percent differences between these concentrations are used to assess
the precision of the monitoring data as described in Sec. 5.1.
3.2 Accuracy of Automated Methods
* * * * *
The audit is made by challenging the analyzer with at least one
audit gas of known concentration (effective concentration for open
path analyzers) from each of the following ranges that fall within
the measurement range of the analyzer being audited:
* * * * *
For point analyzers, the audit shall be carried out by allowing
the analyzer to analyze the audit test atmosphere in its normal
sampling mode such that the test atmosphere passes through all
filters, scrubbers, conditioners, and other sample inlet components
used during normal ambient sampling and as much of the ambient air
inlet system as is practicable. The exception given in Sec. 3.1 for
certain CO analyzers does not apply for audits.
Open path analyzers are audited by inserting a test cell
containing the various audit gas concentrations into the optical
measurement beam of the instrument. If possible, the normally used
transmitter, receiver, and, as appropriate, reflecting devices
should be used during the audit, and the normal monitoring
configuration of the instrument should be modified as little as
possible to accommodate the test cell for the audit. However, if
permitted by the associated operation or instruction manual, an
alternate local light source or an alternate optical path that does
not include the normal atmospheric monitoring path may be used. The
actual concentrations of the audit gas in the test cell must be
selected to produce ``effective concentrations'' in the ranges
specified in this Sec. 3.2. Generally, each audit concentration
measurement result will be the sum of the atmospheric pollutant
concentration and the audit test concentration. If so, the result
must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentration measured by
the instrument immediately before and immediately after the audit
test (or preferably before and after each audit concentration level)
from the audit concentration measurement. If the difference between
the before and after measurements is greater than 20 percent of the
effective concentration of the test gas standard, discard the test
result for that concentration level and repeat the test for that
level. If possible, open path analyzers should be audited during
periods when the atmospheric pollutant concentrations are relatively
low and steady.
Report both the audit test concentrations (effective
concentrations for open path analyzers) and the corresponding
concentration measurements (corrected concentrations, if applicable,
for open path analyzers) indicated or produced by the analyzer being
tested. The percent differences between these concentrations are
used to assess the accuracy of the monitoring data as described in
Sec. 5.2.
* * * * *
Table A-1.--Minimum Data Assessment Requirements
----------------------------------------------------------------------------------------------------------------
Method Assessment method Coverage Minimum frequency Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:
Automated Methods Response check at Each analyzer........ Once per 2 weeks..... Actual
for SO2, NO2, concentration concentration\2\
O3, and CO. between .08 & .10 and measured
ppm (8 & 10 ppm for concentration.\3\
CO)\2\.
Manual methods Collocated samplers.. 1 site for 1-5 sites; Once per week........ Two concentration
including lead. 2 sites for 6-20 measurements.
sites; 3 sites > 20
sites; (sites with
highest conc.).
Accuracy:
Automated Methods Response check at: 1. Each analyzer. 2. 1. Once per year. 2. Actual
for SO2, NO2, .03-.08 ppm,12 .15- 25% of analyzers (at Each calendar concentration\2\
O3, and CO. .20 ppm;12 .35-.45 least 1). quarter. and measured
ppm;12 .80-.90 (indicated)
ppm;12 (if concentration\3\
applicable). for each level.
Manual methods Check of analytical Analytical system.... Each day samples are Actual concentration
for SO2 and NO2. procedures with analyzed, at least and measured
audit standard twice per quarter. (indicated)
solutions. concentration for
each audit
solution.
TSP, PM-10....... Check of sampler flow 1. Each sampler. 2. 1. Once per year. 2. Actual flow rate and
rate. 25% of samplers (at Each calendar flow rate indicated
least 1). quarter. by the sampler.
Lead............. 1. Check sample flow 1. Each sampler. 2. 1. Include with TSP. 1. Same as for TSP.
rate as for TSP. 2. Analytical system. 2. Each quarter. 2. Actual
Check analytical concentration &
system with Pb audit measured
strips. (indicated)
concentration of
audit samples
(g Pb/
strip).
----------------------------------------------------------------------------------------------------------------
\1\Concentration times 100 for CO.
\2\Effective concentration for open path analyzers.
\3\Corrected concentration, if applicable, for open path analyzers.
* * * * *
Appendix B [Amended]
4. Appendix B is amended as follows:
a. The first paragraph of section is revised.
b. Section 3.1 is revised.
c. The text preceding the table in the first paragraph, and the
third, and fourth paragraphs of section 3.2 are revised; and a new
paragraph is added between the third and fourth paragraphs.
d. Table B-1 is revised.
Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
* * * * *
3. Data Quality Assessment Requirements
All ambient monitoring methods or analyzers used in PSD
monitoring shall be tested periodically, as described in this
section 3, to quantitatively assess the quality of the data being
routinely collected. The results of these tests shall be reported as
specified in section 6. Concentration standards used for the tests
must be as specified in section Sec. 2.3. Additional information and
guidance in the technical aspects of conducting these tests may be
found in Reference 3 or in the operation or instruction manual
associated with the analyzer or sampler. Concentration measurements
reported from analyzers or analytical systems must be derived by
means of the same calibration curve and data processing system used
to obtain the routine air monitoring data. Table B-1 provides a
summary of the minimum data quality assessment requirements, which
are described in more detail in the following sections.
3.1 Precision of Automated Methods
A one-point precision check must be carried out at least once
every 2 weeks on each automated analyzer used to measure SO2,
NO2, O3, and CO. The precision check is made by
challenging the analyzer with a precision check gas of known
concentration (effective concentration for open path analyzers)
between 0.08 and 0.10 ppm for SO2, NO2, and O3
analyzers, and between 8 and 10 ppm for CO analyzers. The standards
from which precision check test concentrations are obtained must
meet the specifications of section 2.3. Except for certain CO
analyzers described below, point analyzers must operate in their
normal sampling mode during the precision check, and the test
atmosphere must pass through all filters, scrubbers, conditioners
and other components used during normal ambient sampling and as much
of the ambient air inlet system as is practicable. If permitted by
the associated operation or instruction manual, a CO point analyzer
may be temporarily modified during the precision check to reduce
vent or purge flows, or the test atmosphere may enter the analyzer
at a point other than the normal sample inlet, provided that the
analyzer's response is not likely to be altered by these deviations
from the normal operational mode.
Open path analyzers are tested by inserting a test cell
containing a precision check gas concentration into the optical
measurement beam of the instrument. If possible, the normally used
transmitter, receiver, and, as appropriate, reflecting devices
should be used during the test, and the normal monitoring
configuration of the instrument should be altered as little as
possible to accommodate the test cell for the test. However, if
permitted by the associated operation or instruction manual, an
alternate local light source or an alternate optical path that does
not include the normal atmospheric monitoring path may be used. The
actual concentration of the precision check gas in the test cell
must be selected to produce an ``effective concentration'' in the
range specified above. Generally, the precision test concentration
measurement will be the sum of the atmospheric pollutant
concentration and the precision test concentration. If so, the
result must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentrations measured
by the instrument immediately before and immediately after the
precision check test from the precision test concentration
measurement. If the difference between these before and after
measurements is greater than 20 percent of the effective
concentration of the test gas, discard the test result and repeat
the test. If possible, open path analyzers should be tested during
periods when the atmospheric pollutant concentrations are relatively
low and steady.
If a precision check is made in conjunction with a zero or span
adjustment, it must be made prior to such zero or span adjustment.
The difference between the actual concentration (effective
concentration for open path analyzers) of the precision check gas
and the corresponding concentration measurement (corrected
concentration, if applicable, for open path analyzers) indicated by
the analyzer is used to assess the precision of the monitoring data
as described in 4.1. Report data only from automated analyzers that
are approved for use in the PSD network.
3.2 Accuracy of Automated Methods
Each sampling quarter audit each analyzer that monitors for
SO2, NO2, O3, or CO at least once. The audit is made
by challenging the analyzer with at least one audit gas of known
concentration (effective concentration for open path analyzers) from
each of the following ranges that fall within the measurement range
of the analyzer being audited: * * *
For point analyzers, the audit shall be carried out by allowing
the analyzer to analyze the audit test atmosphere in the same manner
as described for precision checks in Sec. 3.1. The exception given
in Sec. 3.1 for certain CO analyzers does not apply for audits.
Open path analyzers are audited by inserting a test cell
containing an audit gas concentration into the optical measurement
beam of the instrument. If possible, the normally used transmitter,
receiver, and, as appropriate, reflecting devices should be used
during the audit, and the normal monitoring configuration of the
instrument should be modified as little as possible to accommodate
the test cell for the audit. However, if permitted by the associated
operation or instruction manual, an alternate local light source or
an alternate optical path that does not include the normal
atmospheric monitoring path may be used. The actual concentrations
of the audit gas in the test cell must be selected to produce
``effective concentrations'' in the range specified in this section
3.2. Generally, each audit concentration measurement result will be
the sum of the atmospheric pollutant concentration and the audit
test concentration. If so, the result must be corrected to remove
the atmospheric concentration contribution. The ``corrected
concentration'' is obtained by subtracting the average of the
atmospheric concentrations measured by the instrument immediately
before and immediately after the audit test (or preferably before
and after each audit concentration level) from the audit
concentration measurement. If the difference between these before
and after measurements is greater than 20 percent of the effective
concentration of the test gas standards, discard the test result for
that concentration level and repeat the test for that level. If
possible, open path analyzers should be audited during periods when
the atmospheric pollutant concentrations are relatively low and
steady.
The differences between the actual concentrations (effective
concentrations for open path analyzers) of the audit test gas and
the corresponding concentration measurements (corrected
concentrations, if applicable, for open path analyzers) indicated by
the analyzer are used to assess the accuracy of the monitoring data
as described in Sec. 4.2. Report data only from automated analyzers
that are approved for use in the PSD network.
* * * * *
Table B-1.--Minimum PSD Data Assessment Requirements
----------------------------------------------------------------------------------------------------------------
Method Assessment method Coverage Frequency Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:
Automated Methods Response check at Each analyzer........ Once per 2 weeks..... Actual
for SO2, NO2, concentration concentration\2\
O3, and CO. between .08 and .10 and measured
ppm (8 and 10 ppm concentration.\3\
for CO)\2\.
TSP, PM10, Lead.. Collocated samplers.. Highest concentration Once per week or Two concentration
site in monitoring every 3rd day for measurements.
network. continuous sampling.
Accuracy:
Automated Methods Response check at: Each analyzer........ Once per sampling Actual
for SO2, NO2, .03-.08 ppm;\1\\2\ quarter. concentration\2\
O3, and CO. .15-.20 ppm;\1\\2\ and measured
.35-.45 ppm;\1\\2\ (indicated)
.80-.90 ppm;\1\\2\ concentration\3\
(if applicable). for each level.
TSP, PM10........ Sampler flow check... Each sampler......... Once per sampling Actual flow rate and
quarter. flow rate indicated
by the sampler.
Lead............. 1. Sample flow rate 1. Each sampler. 2. 1. Once/quarter. 2. 1. Same as for TSP.
check. 2. Check Analytical system. Each quarter Pb 2. Actual
analytical system samples are analyzed. concentration and
with Pb audit strips. measured
concentration of
audit samples
(g Pb/
strip).
----------------------------------------------------------------------------------------------------------------
\1\Concentration shown times 100 for CO.
\2\Effective concentration for open path analyzers.
\3\Corrected concentration, if applicable, for open path analyzers.
* * * * *
Appendix E [Amended]
5. Appendix E is amended as follows:
a. The title of appendix E is revised.
b. Section 1 is revised.
c. Section 2 is added and sections 3, 5, and 6 are removed and
reserved.
d. Section 4 is revised.
e. In section 7 table 3 is removed and table 4 is redesignated as
table 3.
f. The first paragraph of section 9 is revised.
g. Section 10 is revised.
h. Section 12 is revised.
Appendix E--Probe and Monitoring Path Siting Criteria for Ambient Air
Quality Monitoring
1. Introduction
This appendix contains specific location criteria applicable to
ambient air quality monitoring probes and monitoring paths after the
general station siting has been selected based on the monitoring
objectives and spatial scale of representation discussed in Appendix
D of this part. Adherence to these siting criteria is necessary to
ensure the uniform collection of compatible and comparable air
quality data.
The probe and monitoring path siting criteria discussed below
must be followed to the maximum extent possible. It is recognized
that there may be situations where some deviation from the siting
criteria may be necessary. In any such case, the reasons must be
thoroughly documented in a written request for a waiver that
describes how and why the proposed siting deviates from the
criteria. This documentation should help to avoid later questions
about the validity of the resulting monitoring data. Conditions
under which EPA would consider an application for waiver from these
siting criteria are discussed in section 11 of this appendix.
The spatial scales of representation used in this appendix,
i.e., micro, middle, neighborhood, urban, and regional, are defined
and discussed in Appendix D of this part. The pollutant-specific
probe and monitoring path siting criteria generally apply to all
spatial scales except where noted otherwise. Specific siting
criteria that are phrased with a ``must'' are defined as
requirements and exceptions must be approved through the waiver
provisions. However, siting criteria that are phrased with a
``should'' are defined as goals to meet for consistency but are not
requirements.
* * * * *
2. Sulfur Dioxide (SO2), Ozone (O3), and Nitrogen Dioxide
(NO2)
Additional information on SO2, NO2, and O3
monitor siting criteria may be found in references 11 and 13.
2.1 Horizontal and Vertical Placement. The probe or at least 80
percent of the monitoring path must be located between 3 and 15
meters above ground level. The probe or at least 90 percent of the
monitoring path must be at least 1 meter vertically or horizontally
away from any supporting structure, walls, parapets, penthouses,
etc., and away from dusty or dirty areas. If the probe or a
significant portion of the monitoring path is located near the side
of a building, then it should be located on the windward side of the
building relative to the prevailing wind direction during the season
of highest concentration potential for the pollutant being measured.
2.2 Spacing from Minor Sources (applicable to SO2 and
O3 monitoring only). Local minor sources of SO2 can cause
inappropriately high concentrations of SO2 in the vicinity of
probes and monitoring paths for SO2. Similarly, local sources
of nitric oxide (NO) and ozone-reactive hydrocarbons can have a
scavenging effect causing unrepresentatively low concentrations of
O3 in the vicinity of probes and monitoring paths for O3.
To minimize these potential interferences, the probe or at least 90
percent of the monitoring path must be away from furnace or
incineration flues or other minor sources of SO2 or NO,
particularly for open path analyzers because of their potential for
greater exposure over the area covered by the monitoring path. The
separation distance should take into account the height of the
flues, type of waste or fuel burned, and the sulfur content of the
fuel. It is acceptable, however, to monitor for SO2 near a
point source of SO2 when the objective is to assess the effect
of this source on the represented population.
2.3 Spacing from Obstructions. Buildings and other obstacles
may possibly scavenge SO2, O3, or NO2. To avoid this
interference, the probe or at least 90 percent of the monitoring
path must have unrestricted airflow and be located away from
obstacles so that the distance from the probe or monitoring path is
at least twice the height that the obstacle protrudes above the
probe or monitoring path. Generally, a probe or monitoring path
located near or along a vertical wall is undesirable because air
moving along the wall may be subject to possible removal mechanisms.
A probe must have unrestricted airflow in an arc of at least 270
degrees around the inlet probe, or 180 degrees if the probe is on
the side of a building. This arc must include the predominant wind
direction for the season of greatest pollutant concentration
potential. A sampling station having a probe located closer to an
obstacle than this criterion allows should be classified as middle
scale rather than neighborhood or urban scale, since the
measurements from such a station would more closely represent the
middle scale. A monitoring path must be clear of all trees, brush,
buildings, plumes, dust, or other optical obstructions, including
potential obstructions that may move due to wind, human activity,
growth of vegetation, etc. Temporary optical obstructions, such as
rain, particles, fog, or snow, should be considered when siting an
open path analyzer. Any of these temporary obstructions that are of
sufficient density to obscure the light beam will affect the ability
of the open path analyzer to continuously measure pollutant
concentrations.
2.4 Spacing from Trees. Trees can provide surfaces for
SO2, O3, or NO2 adsorption or reactions and obstruct
wind flow. To reduce this possible interference, the probe or at
least 90 percent of the monitoring path should be 20 meters or more
from the drip line of trees. If a tree or trees could be considered
an obstacle, the probe or 90 percent of the monitoring path must
meet the distance requirements of 2.3 and be at least 10 meters from
the drip line of the tree or trees. Since the scavenging effect of
trees is greater for O3 than for other criteria pollutants,
strong consideration of this effect must be given to locating an
O3 probe or monitoring path to avoid this problem.
2.5 Spacing from Roadways (applicable to O3 and NO2
only). In siting an O3 analyzer, it is important to minimize
destructive interferences from sources of NO, since NO readily
reacts with O3. In siting NO2 analyzers for neighborhood
and urban scale monitoring, it is important to minimize
interferences from automotive sources. Table 1 provides the required
minimum separation distances between a roadway and a probe and
between a roadway and at least 90 percent of a monitoring path for
various ranges of daily roadway traffic. A sampling station having a
point analyzer probe located closer to a roadway than allowed by the
Table 1 requirements should be classified as middle scale rather
than neighborhood or urban scale, since the measurements from such a
station would more closely represent the middle scale. The
monitoring path of an open path analyzer must not cross over a
roadway with an average daily traffic count of 10,000 vehicles per
day or more. In calculating the percentage of a monitoring path over
or near a roadway, one must consider the entire segment of the
monitoring path in the area of potential atmospheric interference
from automobile emissions. Therefore, this calculation must include
the length of the monitoring path over the roadway plus any segments
of the monitoring path that lie in the area between the roadway and
the minimum separation distance, as determined from Table 1. The sum
of these distances must not be greater than 10 percent of the total
monitoring path length.
Table 1.--Minimum Separation Distance Between Roadways and Probes or
Monitoring Paths for Monitoring Neighborhood--and Urban-Scale Ozone and
Nitrogen Dioxide
------------------------------------------------------------------------
Minimum
separation
Roadway average daily traffic, vehicles per day distance\1\,
meters
------------------------------------------------------------------------
10,000......................................... 10
15,000.................................................... 20
20,000.................................................... 30
40,000.................................................... 50
70,000.................................................... 100
110,000........................................ 250
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
values based on the actual traffic count.
2.6 Cumulative Interferences on a Monitoring Path. The
cumulative length or portion of a monitoring path that is affected
by minor sources, obstructions, trees, or roadways must not exceed
10 percent of the total monitoring path length.
2.7 Maximum Monitoring Path Length. The monitoring path length
must not exceed 1 kilometer for analyzers in neighborhood, urban, or
regional scale. For middle scale monitoring sites, the monitoring
path length must not exceed 300 meters. In areas subject to frequent
periods of dust, fog, rain, or snow, consideration should be given
to a shortened monitoring path length to minimize loss of monitoring
data due to these temporary optical obstructions. For certain
ambient air monitoring scenarios using open path analyzers, shorter
path lengths may be needed in order to ensure that the monitoring
station meets the objectives and spatial scales defined for SLAMS in
Appendix D. Therefore, the Regional Administrator or the Regional
Administrator's designee may require shorter path lengths, as needed
on an individual basis, to ensure that the SLAMS meet the Appendix D
requirements. Likewise, the Administrator or the Administrator's
designee may specify the maximum path length used at monitoring
stations designated as NAMS or PAMS as needed on an individual
basis.
* * * * *
4. Carbon Monoxide (CO)
Open path analyzers may be used to measure CO for only middle or
neighborhood scale measurement applications if the open path
analyzer is designated as a SLAMS. Additional information on CO
monitor siting criteria may be found in reference 12.
4.1 Horizontal and Vertical Placement. Because of the
importance of measuring population exposure to CO concentrations,
air should be sampled at average breathing heights. However,
practical factors require that the inlet probe be higher. The
required height of the inlet probe for CO monitoring is therefore
3\1/2\ meter for a microscale site, which is a
compromise between representative breathing height and prevention of
vandalism. The recommended 1 meter range of heights is also a
compromise to some extent. For consistency and comparability, it
would be desirable to have all inlets at exactly the same height,
but practical considerations often prevent this. Some reasonable
range must be specified and 1 meter provides adequate leeway to meet
most requirements.
For the middle and neighborhood scale stations, the vertical
concentration gradients are not as great as for the microscale
station. This is because the diffusion from roads is greater and the
concentrations would represent larger areas than for the microscale.
Therefore, the probe or at least 80 percent of the monitoring path
must be located between 3 and 15 meters above ground level for
middle and neighborhood scale stations. The probe or at least 90
percent of the monitoring path must be at least 1 meter vertically
or horizontally away from any supporting structure, walls, parapets,
penthouses, etc., and away from dusty or dirty areas. If the probe
or a significant portion of the monitoring path is located near the
side of a building, then it should be located on the windward side
of the building relative to both the prevailing wind direction
during the season of highest concentration potential and the
location of sources of interest, i.e., roadways.
4.2 Spacing from Obstructions. Buildings and other obstacles
may restrict airflow around a probe or monitoring path. To avoid
this interference, the probe or at least 90 percent of the
monitoring path must have unrestricted airflow and be located away
from obstacles so that the distance from the probe or monitoring
path is at least twice the height that the obstacle protrudes above
the probe or monitoring path. A probe or monitoring path located
near or along a vertical wall is undesirable because air moving
along the wall may be subject to possible removal mechanisms. A
probe must have unrestricted airflow in an arc of at least 270
degrees around the inlet probe, or 180 degrees if the probe is on
the side of a building. This arc must include the predominant wind
direction for the season of greatest pollutant concentration
potential. A monitoring path must be clear of all trees, brush,
buildings, plumes, dust, or other optical obstructions, including
potential obstructions that may move due to wind, human activity,
growth of vegetation, etc. Temporary optical obstructions, such as
rain, particles, fog, or snow, should be considered when siting an
open path analyzer. Any of these temporary obstructions that are of
sufficient density to obscure the light beam will affect the ability
of the open path analyzer to continuously measure pollutant
concentrations.
4.3 Spacing from Roadways. Street canyon and traffic corridor
stations (microscale) are intended to provide a measurement of the
influence of the immediate source on the pollution exposure of the
population. In order to provide some reasonable consistency and
comparability in the air quality data from microscale stations, a
minimum distance of 2 meters and a maximum distance of 10 meters
from the edge of the nearest traffic lane must be maintained for
these CO monitoring inlet probes. This should give consistency to
the data, yet still allow flexibility of finding suitable locations.
Street canyon/corridor (microscale) inlet probes must be located
at least 10 meters from an intersection and preferably at a midblock
location. Midblock locations are preferable to intersection
locations because intersections represent a much smaller portion of
downtown space than do the streets between them. Pedestrian exposure
is probably also greater in street canyon/corridors than at
intersections. Also, the practical difficulty of positioning
sampling inlets is less at midblock locations than at the
intersection. However, the final siting of the monitor must meet the
objectives and intent of appendix D, sections 2.4, 3, 3.3, and
appendix E, section 4.
In determining the minimum separation between a neighborhood
scale monitoring station and a specific line source, the presumption
is made that measurements should not be unduly influenced by any one
roadway. Computations were made to determine the separation
distance, and table 2 provides the required minimum separation
distance between roadways and a probe or 90 percent of a monitoring
path. Probes or monitoring paths that are located closer to roads
than this criterion allows should not be classified as a
neighborhood scale, since the measurements from such a station would
closely represent the middle scale. Therefore, stations not meeting
this criterion should be classified as middle scale.
Table 2.--Minimum Separation Distance Between Roadways and Probes or
Monitoring Paths for Monitoring Neighborhood Scale Carbon Monoxide
------------------------------------------------------------------------
Minimum
separation
distance\1\
for probes
Roadway average daily traffic, vehicles per day or 90% of a
monitoring
path,
meters
------------------------------------------------------------------------
10,000.......................................... 10
15,000..................................................... 25
20,000..................................................... 45
30,000..................................................... 80
40,000..................................................... 115
50,000..................................................... 135
60,000.......................................... 150
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
values based on the actual traffic count.
4.4 Spacing from Trees and Other Considerations. Since CO is
relatively nonreactive, the major factor concerning trees is as
obstructions to normal wind flow patterns. For middle and
neighborhood scale stations, trees should not be located between the
major sources of CO, usually vehicles on a heavily traveled road,
and the monitor. The probe or at least 90 percent of the monitoring
path must be 10 meters or more from the drip line of trees which are
between the probe or monitoring path and the road and which extend
at least 5 meters above the probe or monitoring path. For microscale
stations, no trees or shrubs should be located between the probe and
the roadway.
4.5 Cumulative Interferences on a Monitoring Path. The
cumulative length or portion of a monitoring path that is affected
by obstructions, trees, or roadways must not exceed 10 percent of
the total monitoring path length.
4.6 Maximum Monitoring Path Length. The monitoring path length
must not exceed 1 kilometer for analyzers used for neighborhood
scale monitoring applications, or 300 meters for middle scale
monitoring applications. In areas subject to frequent periods of
dust, fog, rain, or snow, consideration should be given to a
shortened monitoring path length to minimize loss of monitoring data
due to these temporary optical obstructions. For certain ambient air
monitoring scenarios using open path analyzers, shorter path lengths
may be needed in order to ensure that the monitoring station meets
the objectives and spatial scales defined for SLAMS in Appendix D.
Therefore, the Regional Administrator or the Regional
Administrator's designee may require shorter path lengths, as needed
on an individual basis, to ensure that the SLAMS meet the Appendix D
requirements. Likewise, the Administrator or the Administrator's
designee may specify the maximum path length used at monitoring
stations designated as NAMS or PAMS as needed on an individual
basis.
* * * * *
9. Probe Material and Pollutant Sample Residence Time
For the reactive gases, SO2, NO2, and O3, special
probe material must be used for point analyzers. Studies20-24
have been conducted to determine the suitability of materials such
as polypropylene, polyethylene, polyvinylchloride, Tygon, aluminum,
brass, stainless steel, copper, pyrex glass and teflon for use as
intake sampling lines. Of the above materials, only pyrex glass and
teflon have been found to be acceptable for use as intake sampling
lines for all the reactive gaseous pollutants. Furthermore, EPA\25\
has specified borosilicate glass or FEP teflon as the only
acceptable probe materials for delivering test atmospheres in the
determination of reference or equivalent methods. Therefore,
borosilicate glass, FEP teflon, or their equivalent must be used for
existing and new NAMS or SLAMS.
* * * * *
10. Photochemical Assessment Monitoring Stations (PAMS)
10.1 Horizontal and Vertical Placement. The probe or at least
80 percent of the monitoring path must be located 3 to 15 meters
above ground level. This range provides a practical compromise for
finding suitable sites for the multi-pollutant PAMS. The probe or at
least 90 percent of the monitoring path must be at least 1 meter
vertically or horizontally away from any supporting structure,
walls, parapets, penthouses, etc., and away from dusty or dirty
areas.
10.2 Spacing from Obstructions. The probe or at least 90
percent of the monitoring path must be located away from obstacles
and buildings such that the distance between the obstacles and the
probe or monitoring path is at least twice the height that the
obstacle protrudes above the probe or monitoring path. There must be
unrestricted airflow in an arc of at least 270 deg. around the probe
inlet. Additionally, the predominant wind direction for the period
of greatest pollutant concentration (as described for each site in
section 4.2 of Appendix D) must be included in the 270 deg. arc. If
the probe is located on the side of the building, 180 deg. clearance
is required. A monitoring path must be clear of all trees, brush,
buildings, plumes, dust, or other optical obstructions, including
potential obstructions that may move due to wind, human activity,
growth of vegetation, etc. Temporary optical obstructions, such as
rain, particles, fog, or snow, should be considered when siting an
open path analyzer. Any of these temporary obstructions that are of
sufficient density to obscure the light beam will affect the ability
of the open path analyzer to continuously measure pollutant
concentrations.
10.3 Spacing from Roadways. It is important in the probe and
monitoring path siting process to minimize destructive interferences
from sources of NO since NO readily reacts with O3. Table 4
below provides the required minimum separation distances between
roadways and PAMS (excluding upper air measuring stations):
Table 4.--Separation Distance Between PAMS and Roadways
[Edge of Nearest Traffic Lane]
------------------------------------------------------------------------
Minimum
separation
distance
between
Roadway average daily traffic, vehicles per day roadways
and
stations
in
meters\1\
------------------------------------------------------------------------
<10,000.....................................................>10
15,000...................................................... 20
20,000...................................................... 30
40,000...................................................... 50
70,000...................................................... 100
>110,000.................................................... 250
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
based on the actual traffic flow.
10.4 Spacing from Trees. Trees can provide surfaces for
adsorption and/or reactions to occur and can obstruct normal wind
flow patterns. To minimize these effects at PAMS, the probe or at
least 90 percent of the monitoring path should be placed at least 20
meters from the drip line of trees. Since the scavenging effect of
trees is greater for O3 than for the other criteria pollutants,
strong consideration of this effect must be given in locating the
PAMS probe or monitoring path to avoid this problem. Therefore, the
probe or at least 90 percent of the monitoring path must be at least
10 meters from the drip line of trees that are located between the
urban city core area and the probe or monitoring path along the
appropriate wind direction.
* * * * *
12. Summary
Table 5 presents a summary of the general requirements for probe
and monitoring path siting criteria with respect to distances and
heights. It is apparent from Table 5 that different elevation
distances above the ground are shown for the various pollutants. The
discussion in the text for each of the pollutants described reasons
for elevating the monitor, probe, or monitoring path. The
differences in the specified range of heights are based on the
vertical concentration gradients. For CO, the gradients in the
vertical direction are very large for the microscale, so a small
range of heights has been used. The upper limit of 15 meters was
specified for consistency between pollutants and to allow the use of
a single manifold or monitoring path for monitoring more than one
pollutant.
Table 5.--Summary of Probe and Monitoring Path Siting Criteria
--------------------------------------------------------------------------------------------------------------------------------------------------------
Horizontal and
Height from ground to vertical distance from
Scale [maximum monitoring probe or 80% of supporting structuresB Distance from trees to Distance from roadways
Pollutant path length, meters] monitoring pathA to probe or 90% of probe or 90% of monitoring to probe or monitoring
(meters) monitoring pathA pathA (meters) pathA (meters)
(meters)
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2 CDEF............... Middle [300m] Neighborhood, 3-15.................. >1.................... >10....................... N/A.
Urban, and Regional [1km].
CO DEG................. Micro, Middle [300m], 30.5, 3-15 >1.................... >10....................... 2-10, See Table 1 for
Neighborhood [1km]. middle and
neighborhood scales.
O3CDE.................. Middle [300m], 3-15.................. >1.................... >10....................... See Table 2 for all
Neighborhood, Urban, and scales.
Regional [1km].
Ozone precursors (for Neighborhood and Urban [1 3-15.................. >1.................... >10....................... See Table 4 for all
PAMS)CDE. km]. scales.
NO2CDE................. Middle [300m], Neighborhood 3-15.................. >1.................... >10....................... See Table 2 for all
and Urban [1km]. scales.
PbCDEFH................ Micro; Middle, 2-7 (Micro), 2-15 (All >2 (All scales, >10 (All scales).......... 5-15 (Micro), See
Neighborhood, Urban and other scales). horizontal distance Table 3 for all other
Regional. only). scales.
PM-10CDEFH............. Micro; Middle, 2-7 (Micro), 2-15 (All >2 (All scales, >10 (All scales).......... 2-10 (Micro), See
Neighborhood, Urban and other scales). horizontal distance Figure 2 for all
Regional. only). other scales.
--------------------------------------------------------------------------------------------------------------------------------------------------------
A Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring and all applicable scales for monitoring SO2,
O3, O3 precursors, and NO2.
B When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.
N/A--Not applicable.
C Should be >20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act as an obstruction.
D Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes
above the sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text).
E Must have unrestricted airflow 270 deg. around the probe or sampler; 180 deg. if the probe is on the side of a building.
F The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is dependent
on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur, ash, or
lead content). This criterion is designed to avoid undue influences from minor sources.
G For microscale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at a midblock location.
H For collocated Pb and PM-10 samplers, a 2-4 meter separation distance between collocated samplers must be met.
* * * * *
[FR Doc. 94-20042 Filed 8-17-94; 8:45 am]
BILLING CODE 6560-50-P
