In a series of experiments in an atmospheric simulation chamber (SAPHIR,1 Forschungszentrum Jülich, Germany), NO3 reactivity (kNO3) resulting from the reaction of NO3 with isoprene and stable trace gases formed as products was measured directly using a flow tube reactor coupled to a cavity ring-down spectrometer (FT-CRDS). The experiments were carried out in both dry and humid air with variation of the initial mixing ratios of ozone (50–100 ppbv), isoprene (3–22 ppbv) and NO2 (5–30 ppbv). kNO3 was in excellent agreement with values calculated from the isoprene mixing ratio and the rate coefficient for the reaction of NO3 with isoprene. This result serves to confirm that the FT-CRDS returns accurate values of kNO3 even at elevated NO2 concentrations and to show that reactions of NO3 with stable reaction products like non-radical organic nitrates do not contribute significantly to NO3 reactivity during the oxidation of isoprene. A comparison of kNO3 with NO3 reactivities calculated from NO3 mixing ratios and NO3 production rates suggests that organic peroxy radicals and HO2 account for ∼50 % of NO3 losses. This contradicts predictions based on numerical simulations using the Master Chemical Mechanism (MCM version 3.3.1) unless the rate coefficient for reaction between NO3 and isoprene-derived RO2 is roughly doubled to ∼5×10−12 cm3 molecule−1 s−1.

Full List of Authors and Affiliations:

Patrick Dewald¹, Jonathan M. Liebmann¹, Nils Friedrich¹, Justin Shenolikar¹, Jan Schuladen¹, Franz Rohrer², David Reimer², Ralf Tillmann², Anna Novelli², Changmin Cho², Kangming Xu³, Rupert Holzinger³, François Bernard^4,a, Li Zhou⁴, Wahid Mellouki⁴, Steven S. Brown^5,6, Hendrik Fuchs², Jos Lelieveld¹, and John N. Crowley¹

• ¹Atmospheric Chemistry Department, Max-Planck-Institut für Chemie, 55128 Mainz, Germany
• ²Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
• ³Institute for Marine and Atmospheric Research, IMAU, Utrecht University, Utrecht, the Netherlands
• ⁴Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS (UPR 3021)/OSUC, 1C Avenue de la Recherche Scientifique, 45071 Orléans CEDEX 2, France
• ⁵NOAA Chemical Sciences Laboratory, 325 Broadway, Boulder, CO 80305, USA
• ⁶Department of Chemistry, University of Colorado Boulder, Boulder, CO 80209, USA
• ^anow at: Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Centre National de la Recherche Scientifique (CNRS), Université d'Orléans, Observatoire des Sciences de l'Univers en région Centre – Val de Loire (OSUC), Orléans, France