9520374 Shepson This project aims at improving our understanding of the impact of organic nitrates on the production and distribution of tropospheric ozone. Organic nitrates are produced in the reaction between organic peroxy radicals with nitric oxide, usually as a minor product. The importance of this reaction channel increases with the size of the organic precursor. Removal of nitric oxide through this reaction could constitute an important NOx sink, thus reducing the ozone formation rate. In order to accurately model the ozone budget, the yields of organic nitrates in the oxidation pathways of natural hydrocarbons are needed. In this project, the yield of nitrate formation from isoprene, terpenes, and aromatic hydrocarbons will be measured using a large photochemical reaction chamber equipped with sampling and detection devices capable of distinguishing individual nitrate species. In addition, ambient measurements of organic nitrates will be conducted at a forested site at the northwestern tip of the Michigan southern Peninsula, using a unique combination of adsorbent concentration and chemiluminescent detection that will enable the investigators to measure the total concentration of both gas- and particulate-phase organic nitrates with very low limits of detection. These data will be useful for modeling studies of tropospheric ozone, and will provide new insights into the problem of the speciation of atmospheric total reactive nitrogen (NOy), and the importance of organic nitrates as a sink and/or vehicle for the transport of atmospheric NOx.
