Spatial and temporal variations of PM_2.5 mass closure and inorganic PM_2.5 in the Southeastern U.S

Fine particulate matter (i.e., PM_2.5) has gained extensive attention owing to its adverse effects. The impacts of PM_2.5 may vary in time and space due to the spatiotemporal variations of PM_2.5 number size distribution and chemical compositions. This research analyzed the latest PM_2.5 chemical compositions measurements with an aim to better understand the dynamic changes of PM_2.5 in response to emission reductions due to the new regulations. The particulate measurements from the Southeastern Aerosol Research and Characterization (SEARCH) network between 2001 and 2016 were analyzed for the spatiotemporal variations of PM_2.5 and inorganic PM_2.5 (iPM_2.5 = SO₄^2- + NH₄⁺ + NO₃^-) chemical compositions in the Southeastern United States (U.S.). It was discovered that PM_2.5 and iPM_2.5 mass concentrations exhibited significant downward trends in 2001-2016. Both PM_2.5 and iPM_2.5 mass concentrations were higher at urban and inland sites than rural/suburban and coastal sites. The higher iPM_2.5 concentrations at agricultural sites were attributed to the influences of ammonia (NH₃) emissions from animal feeding operations (AFOs). The iPM_2.5 was the dominant contributor to PM_2.5 in 2001-2016 at the coastal sites, whereas organic carbon matter (OCM) was the major contributor to PM_2.5 after 2011 at the inland sites. Our data analysis suggests that significant decrease of PM_2.5 concentrations is attributed to the reductions in nitrogen oxides (NO_x) and sulfur dioxide (SO₂) emissions in 2001-2016. Findings from this research provide insights into the development of effective PM_2.5 control strategies and assessment of air pollutants exposure.