Estimating ozone and secondary PM2.5 impacts from hypothetical single source emissions in the central and eastern United States

Secondary pollutant impacts from emissions of single sources may need to be assessed to satisfy a variety of regulatory requirements including the Clean Air Act New Source Review and Prevention of Significant Deterioration programs and the National Environmental Policy Act. In this work, single source impacts on O3 and secondary PM2.5 are estimated with annual 2011 photochemical grid model simulations where new hypothetical sources are added to the central and eastern United States with varying precursor emission rates and emission release heights. Impacts from these hypothetical sources are tracked with photochemical grid model source apportionment. Single source impacts on downwind 8-hr maximum O3 tend to increase as emissions of NOX or VOC increase. Downwind impacts on PM2.5 sulfate and nitrate also tend to increase as emissions of SO2 and NOX increase. For all secondary pollutants, impacts from these hypothetical sources tend to decrease as distance from the source increases. However, peak impacts on O3 and secondary PM2.5 are not at the facility fence-line but typically within 50–100 km depending on the emissions rate, precursor pollutant, and emissions release point. Downwind impacts are not uniform directionally from these sources due to varying downwind availability of chemical reactants and prevailing meteorology. Peak impacts for O3 (∼15 ppb) and PM2.5 sulfate (∼8 μg/m3) were within 50 km of these hypothetical sources and peak impacts for PM2.5 nitrate (∼1 μg/m3) were within 125 km. The daily maximum 8-hr O3 and maximum daily average PM2.5 sulfate and nitrate ion impacts for the new hypothetical sources modeled here are generally consistent with those reported in literature. Additional assessments of single source impacts on secondary pollutants are still needed to provide a more comprehensive assessment of different source types and source environments.