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A study of the NOx dependence of isoprene oxidation
Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana, USA
Atmospheric Sciences Department, Tennessee Valley Authority, Muscle Shoals, Alabama, USA
Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA
Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA
Department of Chemistry, University of Michigan, Ann Arbor, Michigan, USA
NOAA Aeronomy Laboratory, Boulder, Colorado, USA
NOAA Aeronomy Laboratory, Boulder, Colorado, USA
Meteorological Service of Canada, Downsview, Ontario, Canada
Sciex, Mississauga, Ontario, Canada
A large set of isoprene and isoprene oxidation product concentration data from four North American sites was examined to assess the NOx dependence of the daytime oxidation of isoprene. Sites that represent a wide range of NOx (50 ppt to 30 ppb) were studied and include the Dickson, Tennessee, and Cornelia Fort Air Park sites during the 1999 Southern Oxidants Study, the Pellston, Michigan, site during the 1998 PROPHET summer intensive, and the Kejimkujik National Park site during the Atlantic 1996 study. Knowledge of NOx and HOx concentrations were critical for this evaluation. While NOx data are readily available at all sites, HOx data are limited. We employed a simple 10-reaction HOx model to calculate steady state OH radical concentrations as a function of [NOx] to enable analysis of the data from all sites. Here, we use methyl vinyl ketone (MVK) concentrations to quantify the extent of isoprene-OH oxidation. Making use of the MVK/isoprene ratio, we show that the rate of production of isoprene oxidation products at various North American sites, although highly variable, exhibits the crossover from NOx-dependent to VOC-dependent conditions at ∼8 ppb [NOx], in agreement with what is calculated from HOx measurements and our calculations.
Received 9 July 2003; accepted 2 March 2004; published 15 June 2004.
Citation: (2004), A study of the NOx dependence of isoprene oxidation, J. Geophys. Res., 109, D11310, doi:10.1029/2003JD003965.
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