2024-19436. Air Plan Approval; Maryland; Determination of Attainment by the Attainment Date for the 2010 1-Hour Primary Sulfur Dioxide National Ambient Air Quality Standard

Table 1—Annual Emissions From Major Stationary SO ₂ Sources in the Anne Arundel-Baltimore County Nonattainment Area for 2012-2021

[Tons of SO ₂ per year]

Year	Brandon Shores		H.A. Wagner				C.P. Crane		Total
	Unit 1	Unit 2	Unit 1	Unit 2	Unit 3	Unit 4	Unit 1	Unit 2
2012	1,547	1,301	0.2	2,513	4,964	41.1	1,214	962	12,542
2013	1,389	1,482	0.2	1,555	8,557	72.7	719	2,143	15,918
2014	1,670	1,475	72.6	1,940	7,277	323	574	1,316	14,648
2015	1,311	1,643	65.0	1,188	8,754	185	382	946	14,474
2016	1,450	1,270	26.5	163	7,575	74.8	412	638	11,609
2017	1,098	1,418	2.5	117	1,245	60.8	379	449	4,769
2018	1,747	1,785	6.1	230	2,733	197	392	475	7,565
2019	547	954	15.3	88.8	1,124	39.9	0	0	2,769
2020	420	267	0	0	605	13.5	0	0	1,306
2021	759	720	5.7	0	645	17.4	0	0	2,147

C. Evaluation of SO₂ Monitoring Data

The 3-year design values of 1-hour SO₂ from 2014-2021 as well as the annual 99th percentile of 1-hour SO₂ concentrations for the Essex Monitor are shown in table 2 in this document. The Essex Monitor has been below the 2010 1-hour SO₂ NAAQS design value since 2012 and has had no hourly SO₂ values exceeding the 75 ppb 2010 1-hour SO₂ NAAQS in the same timeframe. From 2014 to 2020, the Essex Monitor design value has declined from 22 ppb to 9 ppb, representing a decrease of approximately 59%, which could be attributed to the significant decline in operations of the coal fired EGUs in the Area over the past decade. The 2018-2020 design value of 9 ppb represents 12% of the 2010 1-hour SO₂ NAAQS. Since 2014, the Essex Monitor has reliably reported data, collecting and logging data on approximately 95% of days since its installation. This ( print page 72773) represents complete data for monitoring purposes.^[15]

Table 2—2014-2021 Essex Monitor SO ₂ Values for the Anne Arundel-Baltimore County Area

Year	99th Percentile daily 1-hour maximum value (ppb)	Design value (ppb) *	Number of hourly SO 2 values above 75 ppb (by year)	Valid monitor days (by year)
2014	26.4	22	0	360
2015	17.7	22	0	357
2016	12.9	19	0	355
2017	8.5	13	0	323
2018	12.3	11	0	318
2019	10.5	10	0	351
2020	4.7	9	0	352
2021	5.4	7	0	354
* The design value was calculated with the reported year as the final year of the three-year period used in determining the design value ( e.g., 2014 was calculated from the years 2012-2014).

The other monitor in the Area, the special purpose Riviera Beach Monitor, has a 2018-2020 1-hour SO₂ design value of 24 ppb. This monitor was discontinued in mid-2022, precluding the use of a more recent design value. Furthermore, this monitor has experienced significant periods of invalid or missing measurements since its installation in January 2018 and as such, the incorporation of its data into this determination of attainment by the attainment date will be limited to segments of valid and recorded monitoring periods.

The EPA finds the monitoring data from the Essex monitor in the Anne Arundel-Baltimore County Area supports the conclusion that the Area attained the 2010 1-hour SO₂ NAAQS by the September 12, 2021 attainment date.

D. Evaluation of Modeling Data

The EPA conducted a modeling analysis for the CDD proposal ^[16] in July 2022, and as both this action and the CDD largely pertain to the same timeframe, this determination of attainment by the attainment date will utilize the same modeling results. The modeling analysis was based on a combination of actual and allowable emissions for 2019-2021. Concurrent meteorological data for 2019-2021 and appropriate background concentrations were incorporated into the model, and inputs were overlaid into a model receptor grid covering the areas near the sources to adequately capture the maximum modeled concentration. As noted, this modeling analysis followed much of the modeling procedures outlined in Maryland's modeling protocol document and Maryland's original designation modeling analysis. Therefore, this modeling largely follows established model guidelines previously utilized in Maryland's analysis of the Anne Arundel-Baltimore County Area. Additional information on the model assumptions and development is available in the docket for this action.^[17]

The EPA's modeling analysis based on 2019-2021 SO₂ emissions demonstrate a peak design value of 53.1 ppb occurs within the Anne Arundel-Baltimore County Area. This modeled value is approximately 71% of the 75 ppb 2010 SO₂ NAAQS and occurred about one kilometer east of the Fort Smallwood Complex, near the southern shoreline of the Patapsco River. The peak model receptor design value and the 99th percentile model concentrations used in this calculation are summarized in table 3 in this document. It should be noted that the 99th percentile values decline over this modeled period—aligning with the reduced SO₂ emissions from the major stationary sources in the Area.

Table 3—Summary of 2019-2021 Peak Modeled Receptor 1-Hour SO ₂ Design Values and 99th Percentile Values for the Anne Arundel-Baltimore County, MD Area

Design value (ppb)	Year 1			Year 2			Year 3
	Date	Hour of day	SO 2 99th percentile (ppb)	Date	Hour of day	SO 2 99th percentile (ppb)	Date	Hour of day	SO 2 99th percentile (ppb)
53.1	10-02-2019	14	69.3	7-27-2020	12	52.3	1-20-2021	09	37.9

As previously discussed, this CDD modeling data includes approximately 3.5 months of data occurring after the attainment date and does not include approximately 3.5 months of data from September 2018 through December 2018. To ensure consideration of the 36-month period prior to the attainment date, the EPA has analyzed the emissions data of these 3.5 months at the end of 2018. While emissions between these two 36-month periods (September 2018 through September 2021 vs. January 2018 through December 2021) are relatively similar, the substitution of the September through December 2018 data for the September through December 2021 data does represent an approximately 16% increase in the total emissions during the 36-month period utilized for ( print page 72774) assessing timely attainment. This data, compiled from the EPA's Clean Air Markets Program Data,^[18] is available in table 4 in this document and can be compared to the totals for the 2019-2021 timeframe provided in table 1 in this document. The total tons of SO₂ emissions for each of these 1-year (or 12-month) periods on a 2019-2021 calendar-year basis vs. a September 2018 through September 2021 basis, respectively, are as follows: Period 1—2,769 vs. 3,396; Period 2—1,306 vs. 1,764; and Period 3—2,147 vs. 2,083.

Table 4—Emissions From Major Stationary SO ₂ Sources in the Anne Arundel-Baltimore County Nonattainment Area for September 2018 Through September 2021

[Tons of SO ₂ per year]

Time period	Brandon Shores	Wagner	Total *
Sept. 12, 2018-Sept. 11, 2019	1,976.1	1,419.4	3,395.5
Sept. 12, 2019-Sept. 11, 2020	779.3	984.7	1,764.0
Sept. 12, 2020-Sept. 11, 2021	1,608.2	474.5	2,082.7
* C.P. Crane is excluded from this table as the facility had ceased operation by September 12, 2018.