Effects of Sources and Meteorology on Ambient Particulate\nMatter in Austin, Texas

Abstract

We\nmeasured ambient submicron aerosol at an urban background site\nin Austin, Texas in June 2018 (summer) and October–November\n2014 (fall). We report the NR-PM₁ (non-refractory particulate\nmatter with aerodynamic diameter under 1 μm) concentration,\nsize distribution, and bulk composition measured with a quadrupole-aerosol\nchemical speciation monitor and a scanning electrical mobility spectrometer.\nSource apportionment of organic aerosol (OA) using positive matrix\nfactorization (PMF) resolved two oxidized factors, local and regional-OOA,\nfor the summer period and an additional factor, hydrocarbon-like OA\n(HOA), for the fall period. Differences in the diurnal variation of\nthe local-OOA factor during the two periods and the absence of an\nHOA factor in the summer indicate that photochemical processing played\nan important role in governing summer OA composition and diurnal variation.\nConcentrations of particulate sulfate (SO₄^2–) were higher in summer than fall, which may be due to emissions\nfrom cement kilns located upwind of the measurement location under\nthe summer wind conditions. Size distribution data suggest frequent\nnucleation events in summer afternoons, possibly initiated by SO₂ and high photochemical activity, and supported by low particle\nloading and, therefore, a low condensational sink. Overall, we demonstrate\nthe importance of sources, meteorological conditions, and photochemistry\nin governing the composition and concentration of PM₁ at\nthis urban background site.