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Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC4RS) and ground-based (SOAS) observations in the Southeast US.

  • Author(s): Fisher, JA
  • Jacob, DJ
  • Travis, KR
  • Kim, PS
  • Marais, EA
  • Miller, C Chan
  • Yu, K
  • Zhu, L
  • Yantosca, RM
  • Sulprizio, MP
  • Mao, J
  • Wennberg, PO
  • Crounse, JD
  • Teng, AP
  • Nguyen, TB
  • St Clair, JM
  • Cohen, RC
  • Romer, P
  • Nault, BA
  • Wooldridge, PJ
  • Jimenez, JL
  • Campuzano-Jost, P
  • Day, DA
  • Hu, W
  • Shepson, PB
  • Xiong, F
  • Blake, DR
  • Goldstein, AH
  • Misztal, PK
  • Hanisco, TF
  • Wolfe, GM
  • Ryerson, TB
  • Wisthaler, A
  • Mikoviny, T
  • et al.
Abstract

Formation of organic nitrates (RONO2) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NOx), but the chemistry of RONO2 formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO2) in the GEOS-Chem global chemical transport model with ∼25 × 25 km2 resolution over North America. We evaluate the model using aircraft (SEAC4RS) and ground-based (SOAS) observations of NOx, BVOCs, and RONO2 from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO2 species measured during the campaigns. Gas-phase isoprene nitrates account for 25-50% of observed RONO2 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 RONO2 were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO3 accounts for 60% of simulated gas-phase RONO2 loss in the boundary layer. Other losses are 20% by photolysis to recycle NOx and 15% by dry deposition. RONO2 production accounts for 20% of the net regional NOx sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NOx emissions. This segregation implies that RONO2 production will remain a minor sink for NOx in the Southeast US in the future even as NOx emissions continue to decline.

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