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

SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, we refer to the EPA.

I. Background

A. The 2010 1-Hour Primary SO ₂ NAAQS

Under section 109 of the CAA, the EPA has established primary and secondary NAAQS for certain pervasive air pollutants (referred to as “criteria pollutants”) and conducts periodic reviews of the NAAQS to determine whether they should be revised or whether new NAAQS should be established. The primary NAAQS represent ambient air quality standards that the EPA has determined are requisite to protect the public health, while the secondary NAAQS represent ambient air quality standards that the EPA has determined are requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such an air pollutant in the ambient air.

Under the CAA, the EPA must establish a NAAQS for SO₂, which is primarily released to the atmosphere through the burning of fossil fuels by power plants and other industrial facilities. The EPA first established primary SO₂ standards in 1971 at 140 parts per billion (ppb) over a 24-hour averaging period and at 30 ppb over an annual averaging period.

On June 22, 2010, the EPA published in the Federal Register a strengthened, primary 1-hour SO₂ NAAQS, establishing a new standard at a level of 75 ppb, based on the 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations of SO₂ . This revised SO₂ NAAQS provides increased protection of public health, and provided for revocation of the 1971 primary annual and 24-hour SO₂ standards for most areas of the country following area designations under the new NAAQS.

B. Designations, Classifications, and Attainment Dates for the 2010 SO ₂ NAAQS

Following promulgation of a new or revised NAAQS, the EPA is required to designate all areas of the country as either “attainment,” “nonattainment,” or “unclassifiable,” pursuant to CAA section 107(d)(1). On August 5, 2013, the EPA finalized its first round of designations for the 2010 1-hour primary SO₂ NAAQS. In this 2013 action, the EPA designated 29 areas in 16 states as nonattainment for the 2010 1-hour primary SO₂ NAAQS. On July 12, 2016, the EPA finalized its second round of initial designations under the 2010 1-hour primary SO₂ NAAQS, designating an additional four areas as nonattainment, effective September 12, 2016. Included in this second round of designations was the Anne Arundel-Baltimore County Area. This designation was based on the weight of evidence for the Area, including available air quality modeling and ambient air monitoring data from 2013-2015. Pursuant to section 192(a) of the CAA, the attainment date for the Anne Arundel-Baltimore County Area was no later than five years after the effective date of initial designation, or September 12, 2021.

CAA section 191(a) directs states containing an area designated nonattainment for the 2010 1-hour primary SO₂ NAAQS to develop and submit a nonattainment area (NAA) state implementation plan (SIP) to the EPA within 18 months of the effective date of an area's designation as nonattainment. For SO_2, the NAA SIP (also referred to as an attainment plan) must meet the requirements of subparts l and 5 of part D, of title 1 of the CAA, and provide for attainment of the NAAQS by the applicable statutory attainment date, or no later than five years from the effective date of designation. The Maryland Department of Environment (MDE) submitted an attainment plan SIP for the Anne Arundel-Baltimore County Area on January 31, 2020.

When a nonattainment area is attaining the 2010 1-hour primary SO₂ NAAQS based on the most recent available data, the EPA may issue a Clean Data Determination (CDD), suspending certain NAA planning requirements. The EPA issued a CDD for the Anne Arundel-Baltimore County Area based on modeling and monitoring data for the period 2019-2021 via a final rule published on November 2, 2022, and at the same time, approved certain elements of the submitted attainment plan that are not waived by the EPA's CDD policy. Notably, a CDD does not alter the Area's nonattainment designation. For the EPA to redesignate an area to attainment, the state must submit, and the EPA must approve a redesignation request for the Area that meets the requirements of CAA section 107(d)(3). To date, Maryland has not requested redesignation of the Area to attainment.

C. EPA Determination of Attainment by the Attainment Date

Section 179(c)(1) of the CAA requires the EPA to determine whether a nonattainment area attained an applicable standard by the applicable attainment date based on the area's air quality as of the attainment date. The EPA is required to issue this determination within six months of the attainment date. Thus, the EPA had a mandatory duty to determine by March 12, 2022, under CAA section 179(c) if the Area reached attainment. With this action, the EPA proposes to determine, in accordance with CAA section 179(c), that the Anne Arundel-Baltimore County Area attained the 2010 1-hour primary SO₂ NAAQS by the September 12, 2021, attainment date.

A determination of whether an area's air quality meets applicable standards is generally based upon the most recent three years of complete, quality-assured data gathered at established state and local air monitoring stations (SLAMS) in a nonattainment area and entered into the EPA's Air Quality System (AQS) database. Data from ambient air monitors operated by state and local agencies in compliance with the EPA monitoring requirements must be submitted to AQS. Monitoring agencies annually certify that these data are accurate to the best of their knowledge. All data are reviewed to determine the area's air quality status in accordance with 40 CFR part 50, appendix T (for SO₂). In general, for SO₂ the EPA does not rely exclusively on monitoring data to determine whether the NAAQS is met unless it has been demonstrated that the monitors were appropriately sited to record expected maximum ambient concentrations of SO₂ in an area. As such, monitoring data can be supplemented with other relevant information, including dispersion modeling and emissions inventories, for determining attainment.

The attainment date for the Anne Arundel-Baltimore County Area was September 12, 2021. For an area where monitoring data alone is used in the determination of attainment, the three-year design value for the calendar years preceding the attainment date is typically used ( e.g., the design value for January 2018 through December 2020 is the appropriate design value for an attainment date of September 12, 2021). In this case for the Anne Arundel-Baltimore County NAA however, the EPA is relying on both a combination of monitoring data and preexisting modeling from the November 2022 CDD to demonstrate attainment. The modeling for the CDD was for the period January 2019 through December 2021, which includes approximately 3.5 months of data occurring after the attainment date. The use of modeling information from 2021 provides additional credible evidence to demonstrate attainment by the September 12, 2021 attainment date because it is a more current representation of air quality in the area. Additionally, the EPA evaluated emissions from 2018 ( i.e., September 13, 2018 through December 31, 2018) as a crosscheck of the 3.5 months of data that was modeled after the attainment date ( i.e., September 13, 2021 through December 31, 2021) to confirm that the modeling impacts would not have resulted in violations had other time periods been modeled which would have aligned more closely with the monitored design value from 2018-2020.

II. Proposed Determination

A. Area Characterization

The Anne Arundel-Baltimore County Area is located in Maryland along the western banks of the Chesapeake Bay and encompasses portions of Anne Arundel County and Baltimore County within 26.8 kilometers of Herbert A. Wagner's Generating Station (Wagner) unit 3 stack, which is located at 39.17765 N latitude, 76.52752 W longitude. Any portion of Baltimore City that falls within this 26.8-kilometer radius is excluded from the nonattainment area. As noted, this area was designated as nonattainment by the EPA on July 12, 2016 for the 2010 1-hour primary SO₂ NAAQS. A March 2, 2015 Consent Decree and enforceable order issued by the United States District Court for the Northern District of California mandated that the EPA issue designations within 16 months (July 2, 2016) for areas that contained a stationary source that had not been announced for retirement and, according to the EPA's Air Markets Database, emitted either more than 16,000 tons of SO₂ in 2012 or more than 2,600 tons of SO₂ and had an annual average emission rate of at least 0.45 pounds of SO₂ per one million British thermal units (lbs SO₂ /MMBTU) in 2012. In 2012, Wagner emitted 7,514 tons of SO₂ and had an emissions rate of 1.105 lbs SO₂ /MMBTU, and had not been announced for retirement as of March 2, 2015. As a result, the Consent Decree applied to the Anne Arundel-Baltimore County Area.

Including Wagner, the Anne Arundel-Baltimore County Area contains three facilities that emit or have historically emitted SO₂ for the timeframe of interest. Brandon Shores power plant, C.P. Crane (Crane) power plant, and Wagner possess or have possessed coal-fired electric generating units (EGUs). Brandon Shores and Wagner are located next to one another in northern Anne Arundel County near the City of Baltimore on a 456-acre site called the Fort Smallwood Complex. Crane is located approximately 22 kilometers northeast of the Fort Smallwood Complex in Baltimore County.

To aid in assessing if an area is meeting attainment, SLAMS collect ambient air data. One such monitor, the Essex monitor (Air Quality System (AQS) Site ID 24-005-3001), is located in the Anne Arundel-Baltimore County Area. The Essex monitor in Baltimore County is over 15 kilometers northeast of the Fort Smallwood Complex (Brandon Shores and Wagner) and approximately 9 kilometers west of Crane—placing the monitor well away from any primary sources of SO₂ . The Essex monitor's 1-hour SO₂ design values have not violated the 2010 1-hour primary SO₂ NAAQS of 75 ppb over the last decade. The last design value exceedance of the NAAQS for this site was during the 2007-2009 period. Additionally, there is a special purpose monitor in the Area—the Riviera Beach monitor (AQS ID 24-003-2002)—which has only operated since January 2018. It is sited in Anne Arundel County, less than 5 kilometers away from the Fort Smallwood Complex, providing a better estimation of the actual maximum SO₂ concentration within the nonattainment area. While it has not measured any instances exceeding the 2010 1-hour SO₂ NAAQS, it has experienced significant timeframes of invalid or missing measurements and was discontinued in 2022.

As placement of the Essex SLAMS and Riviera Beach special purpose monitor does not capture the location of the maximum ambient SO₂ concentration, modeling may supplement the monitoring data to assist in determining if the Anne Arundel-Baltimore County Area has timely reached attainment. This action utilizes the same modeling as the November 2022 CDD for the Anne Arundel-Baltimore County Area between 2019-2021. This modeling analysis followed much of the modeling procedures outlined in Maryland's SIP modeling protocol document and Maryland's original designation modeling analysis. As such, this modeling largely follows established model guidelines previously utilized in Maryland's analysis of the Anne Arundel-Baltimore County Area.

B. Evaluation of SO ₂ Emissions Data

The EPA evaluated annual SO₂ emissions trends for sources within the Anne Arundel-Baltimore County Area. The annual emissions from 2012-2021 from each major stationary source within the Area are provided in table 1 in this document, along with the total combined emissions from the listed stationary sources. By the end of 2020, total SO₂ emissions within the Area had declined approximately 90% from 2012 levels and approximately 89% from 2016 levels—the year of nonattainment designation. The closure of Crane's coal units by 2018, the conversion of Wagner Unit 2 from coal to natural gas in 2020, and the installation of a dry sorbent injection emission control system for SO₂ on Wagner Unit 3 in 2018 all contributed to this significant reduction. Additionally, the remaining Fort Smallwood Complex coal units have reduced their total annual operating hours under enforceable consent orders, further decreasing SO₂ emissions within the Area.

The reduction in emissions in the 2018-2020 timeframe compared to pre-2018 emissions provides evidence that the Anne Arundel-Baltimore County Area saw air quality improvements in SO₂ levels and supports the finding that the Area attained the 2010 1-hour SO₂ NAAQS by September 12, 2021.