Abstract
Formation of organic nitrates (RONO(2)) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NO(x)), but the chemistry of RONO(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(2)) in the GEOS-Chem global chemical transport model with ∼25 × 25 km(2) resolution over North America. We evaluate the model using aircraft (SEAC(4)RS) and ground-based (SOAS) observations of NO(x), BVOCs, and RONO(2) from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO(2) species measured during the campaigns. Gas-phase isoprene nitrates account for 25-50% of observed RONO(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(2) were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO(3) accounts for 60% of simulated gas-phase RONO(2) loss in the boundary layer. Other losses are 20% by photolysis to recycle NO(x) and 15% by dry deposition. RONO(2) production accounts for 20% of the net regional NO(x) sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NO(x) emissions. This segregation implies that RONO(2) production will remain a minor sink for NO(x) in the Southeast US in the future even as NO(x) emissions continue to decline.