Quantifying the Impact of Emission Sectors and Foreign Inflow to U.S. Air Quality

Several sector-specific model simulations were performed to quantify how emission sectors and global pollution inflow contribute to air pollution episodes across the United States. Using the EPA Community Multiscale Air Quality Model (CMAQ), all simulations were performed using 27 vertical layers and a horizontal resolution of 36 km x 36 km over the continental U.S. for both January and July of 2007. Meteorological data were generated by the Weather Research and Forecasting model (WRF) and integrated with the 2007 emissions inventory from the Lake Michigan Air Directors Consortium (LADCO). Our study focuses on the following sectors: electricity generating units, on-road and off-road transportation (diesel vehicles, gasoline vehicles, and rail), as well as global inflow as simulated by the Model for Ozone and Related Chemical Tracers (MOZART). For each of these sectors, CMAQ was run with sectoral emissions "zeroed out" for comparison with a base case scenario. Base case results are evaluated for nitrogen dioxide (NO2), ozone (O3), and fine particulate matter (PM2.5) species with ground based monitors from the U.S. Environmental Protection Agency's (EPA) Air Quality System (AQS). Total column NO2 is further compared with satellite data obtained from the Ozone Monitoring Instrument (OMI) on the Aura satellite. Comparisons with surface observations show ground-level concentrations that are comparable to measurements taken at EPA monitor locations across most of the U.S. Conclusions on the various emission sectors may provide useful data for air quality managers to make informed decisions for air pollution control strategies.