AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Modeling Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds Above and Below the Canopy during CABINEX 2009
BEN SCHULZE, Henry Wallace, Robert Griffin, Rice University
Abstract Number: 92 Working Group: Aerosol Chemistry
Abstract We developed a zero-dimensional model to investigate nitrate radical (NO$_3) oxidation of isoprene and alpha-pinene above and below the forest canopy during the CABINEX 2009 field campaign in northern Michigan. Predicted NO$_3 concentrations, while relatively low, are two-to-three times higher below the canopy than above during the day. As expected, the hydroxyl radical (OH) is the primary oxidant of isoprene during the day (60-95%) both above and below the canopy. NO$_3 accounts for 0-40% of nighttime isoprene oxidation but has virtually no influence during the day. Ozone (O$_3) is the main oxidant of alpha-pinene (40-70%) in all modeled ambient conditions. Still, NO$_3 contributes 25-40% of nighttime and up to ~10% of daytime oxidation of alpha-pinene below the canopy. In artificially polluted conditions, created by increasing O$_3 and NO$_x profiles by factors of two and five, respectively, below canopy NO$_3 oxidation of alpha-pinene increases to 60-80% of the nighttime total and 20% or more of the daytime total. Midday OH and NO$_3 alpha-pinene oxidation rates are similar in modeled polluted conditions. The pathway for organic nitrate (ON) formation is divided between OH- and NO$_3-initiated oxidation in below canopy ambient conditions; however, in polluted conditions NO$_3 oxidation dominates.