AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Modeling Studies of Isoprene- and Monoterpene-derived Organic Nitrates in a Mixed Forest Environment and the Role of Deposition and Aerosol Multiphase Chemistry
ISAAC CANADA, Paul Shepson, Jonathan Slade, University of California, San Diego
Abstract Number: 385 Working Group: Aerosol Chemistry
Abstract Organic nitrates (RONO2) produced during the oxidation of VOCs in the presence of nitrogen oxides (NOx=NO+NO2) limit ozone production by sequestering NOx and contribute to secondary organic aerosol (SOA) formation. While forested environments represent the largest source of biogenic VOC emissions, and biogenic SOA is the most abundant source of OA in the atmosphere, the formation of biogenic-derived RONO2 is poorly understood with sparse measurements. Here, we present modeling results of RONO2 and compare to measured RONO2 sampled in a mixed deciduous/coniferous forest in northern Michigan during the summer of 2016. During that study, concentrations of hydroxylated RONO2 (HORONO2) resulting from the oxidation of isoprene (IN) and monoterpenes (MTN) were quantified over multiple daily cycles. We apply a 0-D chemical kinetics box model using the Master Chemical Mechanism constrained by measured species and compare our results to those measured. Our results demonstrate the importance of deposition processes, including HORONO2 uptake and loss to the aerosol phase. The results indicate that without aerosol mass, the model overpredicts daytime IN and MTN by close to a factor of two, especially in the early afternoon when aerosol number concentrations are highest. Including depositional loss of IN and MTN to the available aerosol mass as a function of time results in better agreement between the modeled and measured concentrations. These results emphasize the importance of RONO2 multiphase chemistry and likely hydrolysis of HORONO2 in biogenic SOA particles in controlling the NOx and thus ozone budgets in forested environments.