Understanding the Controls over NOx Loss in the Southeast United States

Wednesday, 17 December 2014
Paul Romer1, Kaitlin Duffey1, Paul J Wooldridge2, Philip Allen Feiner3, Li Zhang3, Abigail Koss4, Kevin Frederick Olson1, Robert J Wild5, William H Brune3, Joost A De Gouw6, Allen H Goldstein1, Steven S Brown7 and Ronald C Cohen1, (1)University of California Berkeley, Berkeley, CA, United States, (2)UC Berkeley, Berkeley, CA, United States, (3)Pennsylvania State University Main Campus, University Park, PA, United States, (4)University of Colorado at Boulder, Boulder, CO, United States, (5)Colorado University/NOAA/ESRL, Boulder, CO, United States, (6)NOAA Earth System Research Lab, Boulder, CO, United States, (7)NOAA Earth System Research Lab, Chemical Sciences Division, Boulder, CO, United States
The Southeast United States is an ideal place to study the interactions of anthropogenic and biogenic NOx with high concentrations of biogenic organic compounds. NOx loss processes under these conditions are not well understood and have a large impact on ozone formation and the products of VOC oxidation. We use measurements collected during summer 2013 at a rural forest in Alabama as part of the Southern Oxidant and Aerosol Study (SOAS) to calculate NOx loss rates. In this low-NOx, high-BVOC region, nitric acid formation is a minor loss process during the day and is nearly negligible during the night. Formation of alkyl nitrates, especially isoprene nitrates during the day and monoterpene nitrates during the night, accounts for the large majority(over 80 percent) of NOx loss in this region. This stands out compared to other regions, which have generally either found the alkyl nitrate and nitric acid formation to be roughly equal in importance or nitric acid formation to be the dominant channel for NOx loss. The rapid formation of alkyl nitrates leads to an average afternoon NOx lifetimes of under three hours, and makes the fate of alkyl nitrates crucial for understanding the NOy budget.