AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Reactive Uptake of Ammonia by Secondary Organic Aerosols: Implications for Air Quality
JEREMY HORNE, Shupeng Zhu, Julia Montoya, Mallory Hinks, Sergey Nizkorodov, Donald Dabdub, University of California, Irvine
Abstract Number: 196 Working Group: Urban Aerosols
Abstract In the South Coast Air Basin of California (SoCAB), a large fraction of total PM2.5 mass is comprised of aerosol nitrates, such as ammonium nitrate (NH4NO3). Ammonium nitrate aerosol is formed from the reaction of ammonia (NH3) and nitric acid (HNO3) and can cause adverse health effects and reduce visibility. In the SoCAB, the largest ammonia emissions sources are agricultural activities and automobiles. Although the total automobile and agricultural NH3 emissions are estimated as similar in magnitude, the spatial concentration and high emissions rates of dairy facilities cause downwind NH3 mixing ratios to be a factor of 10 higher than those from automobile emissions sources. The high concentration of ammonia in these plumes drives most of the HNO3 into the particle phase, resulting in high PM2.5 concentrations in the northeast portion of the SoCAB.
While the conversion of inorganic gases into particulate phase sulfate, nitrate, and ammonium is now fairly well understood, there is considerable uncertainty over interactions between gas phase ammonia and secondary organic aerosols (SOA). In this study, the University of California, Irvine - California Institute of Technology (UCI-CIT) regional airshed model is used to investigate the potential air quality impacts of the chemical uptake of ammonia by SOA. A first order loss rate for ammonia onto SOA is implemented into the model based on the NH3 uptake coefficients onto SOA reported in the literature to determine the impact of this process on ammonia and PM2.5 concentrations in southern California. Air quality simulations are performed with a range of uptake coefficients to determine the sensitivity of NH3 removal to the magnitude of the uptake coefficient. The model predicts that the chemical uptake of ammonia by SOA can significantly reduce the concentration of gas-phase ammonia, thereby indirectly affecting the amount of ammonium sulfate and ammonium nitrate in particulate matter.