1167107 - Regional PM_2.5 Budgets in Urban and Rural Sites Across the United States

Characterizing the spatial and seasonal variability in the composition of major aerosol species is essential for estimating their contribution to PM2.5 total mass concentration and visibility degradation. The IMPROVE (Interagency Monitoring of Protected Visual Environments) network, which began in 1988, operates in mostly remote/rural areas throughout the United States. The Chemical Speciation Network (CSN) began in 2000 and is operated by the Environmental Protection Agency at mostly urban/suburban monitoring sites across the United States. The IMPROVE and CSN networks have similar sampling schedules and analysis methods, with 24-hr samples collected with either 1-in-3 day or 1-in-6 day (CSN) frequency. We aggregated data from over 300 sites from both networks to evaluate the regional and monthly variability of major aerosol species and their contribution to the PM2.5 mass budget. Specifically, we examined the 2016-2019 monthly mean mass concentrations of ammonium sulfate, ammonium nitrate, particulate organic matter, elemental carbon, mineral dust aerosols, and sea salt, as well their relative contribution to PM2.5 mass concentrations. Evaluating the monthly mean distributions for major aerosol species as a function of geographic region (especially differences in urban and rural concentrations) is necessary for understanding the impacts of emission sources, regional transport, and atmospheric processes governing aerosol concentrations in the atmosphere.