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Maryland Power Plants and the Environment (CEIR-18)

4.1 Air Quality

4.1.1 Overview

Click to OpenRevised NAAQSThe Clean Air Act (CAA) was the first major federal environmental law in the U.S. that required the development and enforcement of regulations to protect the general public from air pollutants known to harm human health. The CAA authorized the United States Environmental Protection Agency (EPA) to develop ambient air quality standards for six common air pollutants (“criteria” pollutants). These National Ambient Air Quality Standards (NAAQS) represent the maximum pollutant concentrations that are allowable in ambient air. “Primary” NAAQS are based on health risk assessments and are designed to protect public health, including the health of sensitive populations such as asthmatics, children, and the elderly. “Secondary” NAAQS are designed to protect the public welfare by preserving visibility and preventing damage to crops, animals, vegetation, and buildings. The CAA requires EPA to review and, if appropriate, revise the NAAQS every five years. Table 4-1 lists the current NAAQS.

Table 4-1 National Ambient Air Quality Standards as of February 2016

Pollutant Primary/
Averaging Time Level Form
Carbon Monoxide (CO) primary
8 hours 9 ppm Not to be exceeded more than once per year
1 hours 35 ppm
Lead (Pb) primary and secondary Rolling 3 month period 0.15 μg/m3 (1) Not to be exceeded
Nitrogen Dioxide(NO2) primary 1 hour 100 ppb 98th percentile of 1-hour daily maximum concentrations, averaged over 3 years
primary and secondary 1 year 53 ppb (2)
Ozone (O3) primary and secondary 8 hours 0.070 ppm (3) Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years
Particle Pollution (PM) - PM2.5 primary 1 year 12.0 μg/m3 annual mean, average over 3 years
secondary 1 year 15.0 μg/m3 annual mean, average over 3 years
primary and secondary 24 hours 35 μg/m3 98th percentile, average over 3 years
Particle Pollution (PM) - PM10 primary and secondary 24 hours 150 μg/m3 Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide(SO2) primary 1 hour 75 ppb (4) 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
secondary 3 hours 0.5 ppm Not to be exceeded more than once per year

Source: “National Ambient Air Quality Standards.” Reviewing National Ambient Air Quality Standards – Scientific and Technical Information. EPA, 4 March 2016.

ppm - parts per million

ppb - parts per billion
mg/m3 - milligram per cubic meter
μg/m3 - microgram per cubic meter

  1. In areas designated nonattainment for the Pb standards prior to the promulgation of the current (2008) standards, and for which implementation plans to attain or maintain the current (2008) standards have not been submitted and approved, the previous standards (1.5 µg/m3 as a calendar quarter average) also remain in effect.
  2. The level of the annual NO2 standard is 0.053 ppm. It is shown here in terms of ppb for the purposes of clearer comparison to the 1-hour standard level.
  3. Final rule signed October 1, 2015, and effective December 28, 2015. The previous (2008) O3 standards additionally remain in effect in some areas. Revocation of the previous (2008) O3 standards and transitioning to the current (2015) standards will be addressed in the implementation rule for the current standards.
  4. The  previous SO2 standards (0.14 ppm 24-hour and 0.03 ppm annual) will additionally remain in effect in certain areas: (1) any area for which it is not yet 1 year since the effective date of designation under the current (2010) standards, and (2) any area for which implementation plans providing for attainment of the current (2010) standard have not been submitted and approved and which is designated nonattainment under the previous SO2 standards or is not meeting the requirements of a State Implementation Plan (SIP) call under the previous SO2 standards (40 CFR 50.4(3)). A SIP call is an EPA action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the require NAAQS.

The six criteria pollutants, most of which are emitted by fossil fuel-fired power plants, are as follows:

Across the country, EPA and state and local regulatory agencies monitor concentrations of the criteria pollutants near ground level. Ambient monitoring in Maryland is handled by MDE's Ambient Air Monitoring Program. The locations of ambient air monitoring stations in Maryland are shown in Figure 4-1. If monitoring indicates that the concentration of a pollutant exceeds the NAAQS in any area of the country, that area is labeled a “nonattainment area” for that pollutant, meaning that the area is not attaining the national ambient air quality standard. Conversely, any area in which the concentration of a criteria pollutant is below the NAAQS is labeled an “attainment area” for that pollutant.

Figure 4-1 Ambient Pollutant Monitoring Stations in Maryland

Figure 4-1

Source: “Current Ambient Air Monitoring Network Map.” Ambient Air Monitoring Network. MDE. Accessed 21 November 2016.

The attainment/nonattainment designation is made on a pollutant-by-pollutant basis. The air quality in an area, therefore, may be designated as attainment for some pollutants and nonattainment for other pollutants simultaneously. The designation is important because many air regulatory requirements are based in part on whether a source is located in an attainment area, where emissions must be limited to ensure the air stays in attainment with the standards, or in a nonattainment area, where emissions must be reduced to bring the area into attainment. As such, air pollution control requirements are generally more stringent for sources located in nonattainment areas.

Currently, all of Maryland is in attainment with the NAAQS for most of the criteria pollutants (NO2, PM2.5, PM10, CO, and lead). Recently, in June 2016, EPA designated areas in Anne Arundel and Baltimore Counties as nonattainment for 2010 1 hour SO2 NAAQS.  This nonattainment designation was based on air quality modeling of SO2 emissions from the Wagner and Brandon Shores power plants, which are located south of Baltimore in Ann Arundel County.  With the June designation, Baltimore City is now identified as “unclassifiable/attainment” which is an interim designation in situations where there is insufficient data to make a final designation.

In addition to SO2, much of the urbanized portions of Maryland, like most densely populated areas across the eastern U.S., are not meeting the NAAQS for ozone. Ozone is recognized as a regional rather than a local pollutant; thus in the CAA, Congress recognized that ozone pollution and its precursors can be transported from state to state. The Act created the Northeast Ozone Transport Region (OTR), comprised of 12 states (including Maryland) and the District of Columbia. As part of the OTR, the entire state of Maryland must follow nonattainment area requirements as if all areas were ozone nonattainment areas, even though ozone monitoring indicates that many counties are in attainment. Figure 4-2 depicts current 8-hour ozone nonattainment area designations in Maryland.

Figure 4-2 Ozone Nonattainment Areas in Maryland (2008 Standard)

Figure 4-2

“Maryland/Washington D.C./Virginia/Delaware 8-hour Ozone Nonattainment Areas (2008 Standard).” EPA Greenbook. EPA, 22 February 2016. Accessed 10 February 2016.

EPA routinely evaluates the NAAQS to determine whether more stringent or different standards are warranted. For example, EPA has lowered the standard for ozone several times, most recently in October of 2015.

While the NAAQS themselves do not directly affect stationary sources, lowering of the ambient standards means that EPA and states must eventually establish more stringent emissions limits and control technology requirements for sources such as power plants to ensure that ambient standards are met state-wide. This, in turn, likely means additional regulation at the state level of air emission sources in Maryland and throughout the United States.

Revised NAAQS

On December 14, 2012, EPA lowered the fine particulate matter NAAQS by revising the primary annual fine particle (PM2.5) standard to 12 micrograms per cubic meter (μg/m3) from 15 μg/m3 and retaining the 24-hour fine particle standard of 35 μg/m3. EPA also updated monitoring requirements for PM2.5 to include a requirement for monitoring emissions near heavily traveled roads in large urban areas. By 2018, states with nonattainment areas must develop State Implementation Plans (SIPs) showing how the standards will be met. Furthermore, by 2020, states are required to meet the new air quality standards for PM2.5 but may request an extension to 2025 depending upon the severity of PM2.5 pollution.

In 2013, Maryland submitted a request to EPA to redesignate the Washington DC–Maryland–Virginia 1997 PM2.5 nonattainment area to attainment. The request resulted in a revision to Maryland’s attainment status leading ultimately to less restrictive major source permitting requirements.