AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Sensitivity Of Particle pH To NH3: Can High NH3 Cause London Fog Conditions?
Hongyu Guo, Rodney J. Weber, ATHANASIOS NENES, Georgia Institute of Technology
Abstract Number: 587 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract High levels of ammonia (NH3) have been suggested to elevate ambient particle pH levels to near neutral acidity (pH=7), a condition that promotes rapid SO2 oxidation by NO2 to form aerosol sulfate concentration consistent with “London fog” levels. This postulation is tested using aerosol data from representative sites around the world to conduct a thorough thermodynamic analysis of aerosol pH and its sensitivity to NH3 levels. We find that particle pH, regardless of ammonia levels, is always acidic even for the unusually high NH3 levels found in Beijing and Xi’an (pH=4.5-5), locations where sulfate production from NOx is proposed. Therefore, major sulfate oxidation through a NO2-mediated pathway is not likely in China, or elsewhere (e.g., US, Mediterranean) where the aerosol is consistently more acidic. The limited alkalinity from the carbonate buffer in dust and seasalt can provide the only likely set of conditions where NO2-mediated oxidation of SO2 outcompetes with other well-established pathways. The mildly acidic levels associated with excessive amounts of ammonia can promote high rates of SO2 oxidation through transition metal chemistry, this may be an alternative important aerosol chemical contributor to the extreme pollution events.