Air Quality In Dc: Naaqs Criteria Pollutants Exceeded?

The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or criteria pollutants, that are common in outdoor air and harmful to public health and the environment. These pollutants are particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. Criteria pollutants are common across the United States and much of the world, and they are generally combustion products released by the burning of fossil fuels. While I could not find specific information about DC, it is known that certain areas of California and New Hampshire have been designated as nonattainment for NAAQS in the past.

Particulate matter

The Clean Air Act requires the Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also known as "criteria" air pollutants. These pollutants are particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.

The EPA first established NAAQS for particulate matter in 1971, and the standards have been periodically reviewed and revised since then. The primary standards are meant to protect against fine and coarse particle exposures, with the EPA proposing to retain the current standards without revision in 2020. The EPA also announced plans to hold virtual public hearings on the proposed rule.

In 2024, the EPA strengthened the NAAQS for particulate matter to better protect public health. The primary (health-based) annual PM2.5 standard was set at 9.0 micrograms per cubic meter, providing increased protection against harmful health impacts. The EPA also revised the Air Quality Index to improve public communications about the risks of PM2.5 exposures and made changes to enhance air quality protection in communities heavily impacted by air pollution.

Ozone

The National Ambient Air Quality Standards (NAAQS) are standards established by the Environmental Protection Agency (EPA) to protect public health and welfare by regulating the emission of harmful pollutants. The EPA first established primary and secondary NAAQS for photochemical oxidants in 1971, setting both primary and secondary standards at 0.08 ppm as a 1-hour average, not to be exceeded more than one hour per year. The EPA has since revised these standards several times to provide better protection for public health and welfare.

In 2008, the EPA lowered the primary NAAQS for ozone to 75 parts per billion (ppb), expressed as the fourth-highest daily maximum 8-hour average over a 24-hour period. This standard was upheld by the U.S. Court of Appeals for the District of Columbia Circuit in 2013. In 2014, the EPA proposed revisions to the primary and secondary O3 NAAQS and provided a 3-month period for public comments. After considering the public comments and advice from the Clean Air Scientific Advisory Committee (CASAC), the EPA revised the suite of standards for O3 in 2015, setting the primary and secondary NAAQS for O3 at 0.070 parts per million (ppm), retaining their indicators, forms, and averaging times.

The EPA has also established one-hour ozone attainment demonstrations for metropolitan areas, including Washington, D.C. These demonstrations involve modelled attainment or exceedance tests to determine if an area is violating the standard. A predicted concentration above 0.124 ppm ozone indicates that the area is expected to exceed the standard. In 2019, the EPA approved the redesignation of the Washington, D.C. area for the 2008 federal ozone standard, indicating that the area had achieved attainment for the NAAQS for ozone.

Nitrogen oxides

The Clean Air Act requires the EPA to set NAAQS for six principal pollutants or "criteria pollutants" that are common in outdoor air, harmful to public health and the environment, and that come from numerous and diverse sources. These criteria pollutants, which include NOx, are found all over the United States and can cause adverse health effects, environmental damage, and property damage.

The EPA has established primary and secondary NAAQS for nitrogen dioxide (NO2), one of the key pollutants within the NOx family. Primary standards are designed to protect public health, especially sensitive populations such as asthmatics, children, and the elderly, by ensuring an adequate margin of safety. Secondary standards, on the other hand, focus on protecting public welfare, including soils, water, crops, vegetation, animals, wildlife, visibility, and property from the harmful effects of air pollution.

To meet these standards, state, local, and tribal agencies develop emission reduction strategies, plans, and programs. The Menu of Control Measures (MCM) provides these agencies with existing emission reduction measures and relevant information on their efficiency and cost-effectiveness. By implementing these measures, agencies work towards attaining and maintaining the NAAQS for nitrogen dioxide and other criteria pollutants, ensuring better air quality and protecting public health and the environment.

Sulfur oxides

The EPA's 2012 decision to retain the existing standards for sulfur oxides was challenged by the Center for Biological Diversity and other environmental groups, who argued that the standards were not adequate to protect against adverse public welfare effects such as damage to sensitive ecosystems.

In 2019, the EPA reviewed the existing primary NAAQS for sulfur dioxide and decided to retain it, judging that the current NAAQS protects public health with an adequate margin of safety, including the health of at-risk populations with asthma. The standard, established in 2010, is 75 parts per billion based on the 3-year average of the 99th percentile of the yearly distribution of 1-hour daily maximum concentrations.

In April 2024, the EPA proposed to revise the secondary NAAQS for SO2 for the first time since 1971, while retaining the existing secondary standards for oxides of nitrogen and particulate matter. The EPA is finalizing revisions to the data handling requirements for the secondary SO2 NAAQS, which will be effective on January 27, 2025. The revised standard will be an annual average, averaged over three consecutive years, with a level of 10 parts per billion (ppb).

The EPA has also promulgated the Clean Air Interstate Rule (CAIR) to require additional SO2 emission reductions in the eastern half of the United States. Currently, several areas are designated as being in nonattainment of the primary SO2 NAAQS, and certain states are required to develop and implement specific air pollution control measures to reduce ambient SO2 concentrations.

Carbon monoxide

The NAAQS standard for carbon monoxide in outdoor air is 9 ppm over 8 hours and 35 ppm over 1 hour, not to be exceeded more than once a year. The EPA's decision to retain the existing NAAQS for CO in 2011 was based on a review of the air quality criteria for CO.

Historically, areas in Connecticut, such as Hartford, New Haven, Bridgeport, and Stamford, experienced the highest CO levels in New England. In the early 1980s, these areas had many days above the NAAQS, but concentrations have since dropped significantly, and Connecticut is now designated as an attainment area for carbon monoxide. The number of exceedances of the CO NAAQS in the United States dropped by 95% between 1988 and 1997, and all CO monitors in New England are currently well below the standard.

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