Abstract

A global 3-D chemistry and transport model, STOCHEM integrated with a detailed VOC oxidation scheme (CRI v2-R5) has been employed to study the important NO_x reservoir compound, peroxyacetyl nitrate (PAN). Globally, PAN is produced entirely by the reaction of acetyl peroxy radicals (CH₃CO₃) with NO₂ and up to 2.0 ppb of PAN is found over the polluted regions of North America during June- July-August for the present scenario. The imbalances between model and measurement data are noted, with STOCHEM-CRI overestimating PAN mixing ratios relative to the measurement data by +17 and +80 pptv for the lower and upper troposphere, respectively. The inclusion of additional HO_x recycling mechanisms (e.g. related to isoprene oxidation) in STOCHEM-CRI causes a decrease in PAN in a present scenario by as much as 40% over sink regions and reduces the model-measurement disagreement by 90% for the lower troposphere and 40% for the upper troposphere. The lower NO_x emissions and CH₃CO₃ formation upon including HO_x recycling in a preindustrial scenario led to a decrease in PAN formation by as much as 40%. The decrease in PAN formation results in less nitrogen being transported to remote regions which in turn leads to the greatest percentage change in O₃ concentration (9% decrease) in the equatorial regions.