Attributing Ozone Air Quality Nonattainment to Interstate Transport of Pollutants for the Mid-Atlantic Region

Ozone, one of the serious air pollutants related with adverse human health, is formed in the atmosphere through photochemical reactions. Observations show that summertime ozone has caused nonattainment of National Ambient Air Quality Standards (NAAQS) over the Mid-Atlantic region in the U.S. The goal of this study is to investigate the effect of interstate transport of air pollutants on ozone air quality attainment in Mid-Atlantic region using two gas-phase chemical mechanisms (CB 05; Carbon Bond Mechanism, version V and SAPRC-99; Statewide Air Pollution Research Center, version 99). As one of the important components in air quality models, a gas-phase chemical mechanism is used to describe how the secondary pollutants such as ozone and particulate matter are formed through photochemical transformation of pollutant emissions, especially nitrogen oxides, sulfur oxides and volatile organic compounds. In this research, we used the U.S. Environmental Protection Agency's (EPA) regional air quality model, Community Multiscale Air Quality Model (CMAQ ) version 4.7.1 to simulate ambient ozone formation during the period of June 1st to August 31th, 2007. The modeling domain covered the Eastern U.S. and was divided into four regions (CENRAP, LADCO, MANE-VU and SEMAP). The decoupled direct method 3D (DDM-3D) in CMAQ v4.7.1 was used to investigate how peak ozone levels in the Mid-Atlantic region respond to changes in emissions from the four regions. The results show that ozone air quality nonattainment in the Mid-Atlantic area was attributed by anthropogenic precursor emissions from the MANE-VU, LADCO and SEMAP regions. Specifically, the high ozone levels in the Mid-Atlantic region were attributed to anthropogenic NOx and VOC emissions from the MANE-VU region. It's expected that reductions in anthropogenic NOx and VOC emissions from the MANE-VU would be effective for improving ozone air quality over the nonattainment areas in the Mid-Atlantic region. A detailed comparison of the ozone responses to emission changes using the two different chemical mechanisms will also be presented.