Changes of Submicron Particulate Matter in Summer Atlanta - Measurement Results by Aerosol Mass Spectrometer from Six Field Campaigns in the Last Decade

YUTONG LIANG, Jean Rivera-Rios, Tianchang Xu, Masayuki Takeuchi, Taekyu Joo, Lu Xu, Nara Shin, Sabrina Westgate, David Pando, Azin Eftekhari, Na Rae Choi, Seongbin Jo, Anna Kaehr, Yuyang Peng, Nidhi Desai, Aryiana Moore, Jennifer Kaiser, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 209
     Working Group: Urban Aerosols

Abstract
The concentration of submicron particulate matter (PM₁) in summer Atlanta has been declining over the last decade. Organic aerosol (OA), the main component of PM₁ in Atlanta, mainly comes from the oxidation of biogenic emissions. OA in summer Atlanta also shows a declining trend, though the biogenic emissions are not expected to substantially change. The reduction in OA is expected to be related to the reduction of sulfur dioxide and nitrogen oxides from anthropogenic sources, which are crucial in biogenic secondary organic aerosol (SOA) formation. However, to what extent the change in PM₁ is driven by the change in biogenic SOA remains unclear.

In this study, we focus on measurements of submicron non-refractory PM (NR-PM₁) by High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) in six field campaigns in summer Atlanta (from 2012-2022) to determine which aerosol components are responsible for the decrease of NR-PM₁. We determined the sources of OA using positive matrix factorization (PMF) and identified five subtypes of OA. We found that the reductions of sulfate and isoprene-SOA dominate the reduction of NR-PM₁. The concurrent reduction of isoprene-SOA and sulfate is consistent with the role of sulfate in the formation of isoprene-SOA. We also decoupled the meteorological effects from the long-term trend caused by emission reduction using a machine learning model. Modeling results suggest that the long-term trend is the main factor explaining the variation of NR-PM₁ and its components in the decadal dataset, and the reductions of sulfate and isoprene-SOA also dominate the decrease of de-weathered NR-PM1. However, the reduction rate of deweathered OA (0.3 µg m^-3 year^-1) is smaller than the reduction of observed OA (0.4 µg m^-3 year^-1), indicating that weather should be considered when assessing the effect of emission changes on air pollution.