AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aerosol pH Buffering in the Southeastern US: Fine Particles Remain Highly Acidic Despite Large Reductions in Sulfate
ATHANASIOS NENES, Hongyu Guo, Armistead G. Russell, Rodney J. Weber, Georgia Institute of Technology
Abstract Number: 594 Working Group: The Role of Water in Aerosol Chemistry
Abstract pH is a primary aerosol property which controls various atmospheric processes, including secondary organic aerosol formation, gas-particle phase partitioning, and mineral dust or redox metal mobilization. Using a comprehensive data set from the Southern Oxidant and Aerosol Study (SOAS) as the basis for the thermodynamic modeling, we found that particles are highly acidic year around in the southeastern US, with pH typically ranging between 0 and 3. SO42- and NH4+ are the main acid-base components that determine particle pH, however atmospheric concentrations are changing in response to emissions controls. More than 15 years network data have shown a ~70% decrease of SO42- over the southeastern US. This has led to a view that particles will approach neutralization. However, sensitivity analysisto changing SO42- concentrations using thermodynamic modeling, and both detailed SOAS data and longer term monitoring data in the southeastern US indicates that on average particles have remained highly acidic over the past decade, despite the large reductions of SO42-. Gas-phase NH3 is predicted to be fairly constant in the past decade as deposition roughly balances emissions, consistent with observed data. With reductions of SO42- and relatively constant emissions of NH3 in the future, particle acidity will continue to be a highly buffered system with pH predicted to be close to current levels, until SO42- drops to a very low continental background, about 0.3 micro-g per cubic meter. The result reshapes our expectation of future particle pH and implies that present particle acidity related atmospheric processes will remain effective for some time into the future.