AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Modeling NH4NO3 in the San Joaquin Valley during the 2013 DISCOVER-AQ Field Campaign
JAMES KELLY, John Nowak, David Miller, Kang Sun, Mark Zondlo, Caroline Parworth, Qi Zhang, Andrew Weinheimer, Sally Pusede, Ronald Cohen, Gail Tonnesen, Luke Valin, Jesse Bash, Kirk Baker, James Crawford, US EPA
Abstract Number: 288 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract The San Joaquin Valley (SJV) of California is in non-attainment of the 24-hr and annual PM2.5 U.S. National Ambient Air Quality Standards due in part to prolonged periods of elevated NH4NO3 concentrations in winter months. Simulating the processes that lead to elevated NH4NO3 in SJV is challenging due to the complex terrain, diverse emission sources, and stagnant meteorological conditions during the wintertime episodes of high PM2.5 concentrations. A rich dataset of observations related to NH4NO3 formation was acquired during multiple periods of elevated PM2.5 during the DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) field campaign in SJV in January and February 2013. The DISCOVER-AQ dataset is used here to evaluate predictions of NH4NO3 and its precursors from the Community Multiscale Air Quality (CMAQ) model version 5.1 with 4-km horizontal resolution. NOy predictions are in reasonable agreement with measurements from the P3 aircraft, and spatial patterns of NH3 predictions are consistent with measurements from a mobile ground laboratory. However, NH3 mixing ratios are underestimated in source regions. Predictions of the gas-particle partitioning of total nitrate (NO3- + HNO3) are in reasonable agreement with measurements in Fresno, as are predictions of elevated PM2.5 NO3- during a period in January. However, NO3- concentrations are underpredicted in Fresno during a high PM2.5 episode in February, possibly due to issues with modeled meteorology. Modeled chemical production of HNO3 is relatively important from the reaction of OH with NO2 during daytime in the surface layer over major urban centers and from N2O5 hydrolysis during nighttime in the residual layer over relatively rural areas. Model predictions suggest that NO3- formed in the relatively rural areas can sometimes be transported to the urban centers and influence urban PM2.5 concentrations.