Comparison of Models, Theory, Experiment, and Field Observations of Isoprene Nitrates

We have conducted chromatographic separation and quantitative determination of isoprene nitrates from laboratory irradiations of isoprene/NOx/air mixtures, in ambient air at the PROPHET site in Pellston, MI, and at the SOS99 Dickson, TN field site. In 1998 and 2000 isoprene nitrates were determined at the PROPHET site, using independent methods, with similar results. In each case, only three isomers represented the majority of the total isoprene nitrate concentration, although there are 8 different isomers possible. In this paper we compare the results of laboratory studies and field observations with published computational studies of the distribution of isoprene peroxy radicals. We will also discuss the results of a zero-D modeling study of explicit isoprene chemistry applied to the PROPHET data sets, to enable comparison of the individual isoprene nitrate isomer concentrations with model simulation results. The results of the modeling study will be examined with respect to the distribution of biogenic organic nitrates at the PROPHET site, and the impact that deposition of these nitrogen species may have on forest nitrogen cycling.