Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft observations in the Southeast US

• Published in: Atmospheric chemistry and physics 2016-05, Vol.16 (9), p.5969
• Main Authors: Fisher, Jenny A, Jacob, Daniel J, Travis, Katherine R, Kim, Patrick S, Marais, Eloise A, Chan Miller, Christopher, Yu, Karen, Zhu, Lei, Yantosca, Robert M, Sulprizio, Melissa P, Mao, Jingqiu, Wennberg, Paul O, Crounse, John D, Teng, Alex P, Nguyen, Tran B, St. Clair, Jason M, Cohen, Ronald C, Romer, Paul, Nault, Benjamin A, Wooldridge, Paul J, Jimenez, Jose L, Campuzano-Jost, Pedro, Day, Douglas A, Hu, Weiwei, Shepson, Paul B, Xiong, Fulizi, Blake, Donald R, Goldstein, Allen H, Misztal, Pawel K, Hanisco, Thomas F, Wolfe, Glenn M, Ryerson, Thomas B, Wisthaler, Armin, Mikoviny, Tomas
• Format: Article
• Language: English
• Subjects: Aircraft; Analysis; Nitrates; Nitrogen oxides; Photolysis; Troposphere; Volatile organic compounds
• ISSN: 1680-7316; 1680-7324

Formation of organic nitrates (RONO.sub.2) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NO.sub.x ), but the chemistry of RONO.sub.2 formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO.sub.2) in the GEOS-Chem global chemical transport model with  ∼  25  ×  25 km.sup.2 resolution over North America. We evaluate the model using aircraft (SEAC.sup.4 RS) and ground-based (SOAS) observations of NO.sub.x, BVOCs, and RONO.sub.2 from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO.sub.2 species measured during the campaigns. Gas-phase isoprene nitrates account for 25-50 % of observed RONO.sub.2 in surface air, and we find that another 10 % is contributed by gas-phase monoterpene nitrates. Observations in the free troposphere show an important contribution from long-lived nitrates derived from anthropogenic VOCs. During both campaigns, at least 10 % of observed boundary layer RONO.sub.2 were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO.sub.3 accounts for 60 % of simulated gas-phase RONO.sub.2 loss in the boundary layer. Other losses are 20 % by photolysis to recycle NO.sub.x and 15 % by dry deposition. RONO.sub.2 production accounts for 20 % of the net regional NO.sub.x sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NO.sub.x emissions. This segregation implies that RONO.sub.2 production will remain a minor sink for NO.sub.x in the Southeast US in the future even as NO.sub.x emissions continue to decline.