Response of fine particulate matter to emission changes of oxides of nitrogen and anthropogenic volatile organic compounds in the eastern United States.

A three-dimensional chemical transport model (Particulate Matter Comprehensive Air Quality Model with Extensions [PMCAMx]) is used to investigate changes in fine particle (PM2.5) concentrations in response to 50% emissions changes of oxides of nitrogen (NOx) and anthropogenic volatile organic compounds (VOCs) during July 2001 and January 2002 in the eastern United States. The reduction of NOx emissions by 50% during the summer results in lower average oxidant levels and lowers PM2.5 (8% on average), mainly because of reductions of sulfate (9-11%), nitrate (45-58%), and ammonium (7-11%). The organic particulate matter (PM) slightly decreases in rural areas, whereas it increases in cities by a few percent when NOx is reduced. Reduction of NOx during winter causes an increase of the oxidant levels and a rather complicated response of the PM components, leading to small net changes. Sulfate increases (8-17%), nitrate decreases (18-42%), organic PM slightly increases, and ammonium either increases or decreases a little. The reduction of VOC emissions during the summer causes on average a small increase of the oxidant levels and a marginal increase in PM2.5. This small net change is due to increases in the inorganic components and decreases of the organic ones. Reduction of VOC emissions during winter results in a decrease of the oxidant levels and a 5-10% reduction of PM2.5 because of reductions in nitrate (4-19%), ammonium (4-10%), organic PM (12-14%), and small reductions in sulfate. Although sulfur dioxide (SO2) reduction is the single most effective approach for sulfate control, the coupled decrease of SO2 and NOx emissions in both seasons is more effective in reducing total PM2.5 mass than the SO2 reduction alone.