Atmospheric Oxidation in a Southeastern US Forest: Examination of the Discrepancies Between Modeled and Observed OH in a Forest Environment

Wednesday, 17 December 2014
Philip Allen Feiner1, William H Brune1, Li Zhang2, David O Miller1, Paul O Wennberg3, Alex Teng3, Tran Nguyen3, John Crounse3, Jason Michael St Clair3, Ronald C Cohen4, Kaitlin Duffey5, Paul Romer4, Allen H Goldstein4, Pawel K Misztal5, Kevin Frederick Olson6, Frank N Keutsch7, Kate Skog8, Joost A De Gouw9 and Abigail Koss10, (1)Pennsylvania State University Main Campus, University Park, PA, United States, (2)Pennsylvania State Univ, University Park, PA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)University of California Berkeley, Berkeley, CA, United States, (5)UC Berkeley, Berkeley, CA, United States, (6)University of California, Berkeley, CA, United States, (7)UW Madison, Madison, WI, United States, (8)UW-Madison, Madison, WI, United States, (9)NOAA Earth System Research Lab, Boulder, CO, United States, (10)University of Colorado at Boulder, Boulder, CO, United States
Significant oxidation chemistry occurs in the atmosphere in and above forests. In forests where levels of nitrogen oxides (NOx) are low, this chemistry is influenced primarily by the emissions and chemistry of highly reactive Biogenic Volatile Organic Compounds (BVOCs), which both destroy hydroxyl (OH, the main oxidant), and may produce it. Quantifying OH in forest environments is crucial to a proper understanding of the specific oxidation mechanisms taking place. In some other low-NOx / high-BVOC environments, OH measurements have been found to be several times higher than predicted by models, leading to concern that perhaps the current BVOC oxidation mechanisms are missing some OH-producing chemistry. The Southern Oxidant and Aerosol Study (SOAS) presents an excellent opportunity to closely examine these mechanisms as well as the recycling of OH thanks to its extensive suite of measurements taken in an Alabama forest during summer 2013. OH and HO2 measurements made with the Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS) are compared to the results of a photochemical box model constrained by the other measurements taken at SOAS. For this presentation, we examine the discrepancy between the measurements and the model output and discuss potential sources for this discrepancy.