Insights from Eight Years of Aerosol Composition Measurements at SGP: Aerosol Chemistry, Sources, Processes, and Seasonal Trends

Description

An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) has been operated continuously at the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) site since 2011, providing real-time measurements of non-refractory submicron aerosol (NR-PM1) species, such as sulfate, nitrate, ammonium, chloride, and organics, at ~30 min time resolution. Here, we present the main findings from analyzing this rich, long-term measurement dataset of aerosol mass concentration and chemical composition, in conjunction with co-located measurements of other aerosol properties (e.g., aerosol optical properties) and meteorological conditions. NR-PM1 mass concentration and composition at SGP show diurnal and seasonal variation trends which appear to be mainly driven by changes in the emission sources and atmospheric processing of aerosol particles and their precursors. Organic aerosol (OA) is a major aerosol component for the most of the time while the mass fraction of ammonium nitrate in NR-PM1 increases substantially during winter months due to cooler temperatures as well as transport of precursor species from surrounding urban and agricultural areas. Sulfate mass concentration changes substantially from month to month but shows no clear seasonal dependence, probably due to mixed regional and local sources. Positive Matrix Factorization (PMF) analysis of the ACSM measurements reveals that the OA at SGP is composed primarily of oxygenated OA with episodes of enhanced biomass burning OA (BBOA) during winter and spring. Significant correlations are observed between aerosol chemical composition and aerosol optical and microphysical properties. Understanding these correlations based on the extremely rich aerosol and atmospheric radiation measurement data available at SGP may shed important light on aerosol’s direct and indirect effects on climate.