Nitrogen oxides (NOx) are a group of gases that contribute to and impact air pollution and tropospheric ozone. In the atmosphere, NOx can react to form acyl peroxynitrates (APNs). APNs have certain properties that allow them to be transported long distances and, after oxidizing, act as new sources of NOx in these far away regions. Trees, however, can potentially remove APNs, and thus NOx, from the atmosphere by the means of dry deposition. If APN uptake by trees is quicker than oxidation, then tree deposition could serve as a removal mechanism of NOx from the atmosphere. Researchers funded in part by CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) program performed laboratory experiments to study how California trees can remove APNs from the atmosphere. Their results, published in ACS Earth and Space Chemistry, show that APN deposition to California-native trees occurs dominantly at a leaf’s stomata, or opening in the ‘skin’ of the leaf. As such, APN may act as a NOx sink rather than a reservoir in rural and remote forested regions, as trees will remove APN from the atmosphere before APN has a chance to oxidize and release NOx.
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