Changing isoprene and a-pinene ambient concentrations as forest succession occurs and potential effects on secondary organic aerosols.

Abstract

Volatile organic compounds (VOCs) have a large impact on atmospheric composition. They react in a series of complex reactions with radicals to form oxidants, including ozone, and secondary organic aerosols (SOA). The VOCs of interest in this study were isoprene (emitted predominantly by aspen and oak in the sampling area) and a-pinene, a monoterpene (emitted by conifers). During the summer of 2006, the surrounding forest is mainly mixed deciduous in succession towards a more conifer dominated stand. A change in tree composition is expected to lead to an alteration in VOC levels, with monoterpene levels, including a-pinene, increasing relative to isoprene levels. Additionally, since monoterpenes are precursors to secondary organic aerosols (SOA), increases in their emissions may lead to increases in SOA formation. Originally, the ratio of isoprene to a-pinene ambient levels was to be investigated to see if there was evidence for a change in VOC levels that might reflect a change in forest composition between 1998 and 2006. Due to the detection limit of the instrumentation being too high, a-pinene data from the summer of 2006 was not found. The ratios of isoprene to a-pinene from the summer of 1998 were still analyzed and it was found that they varied diurnally and depended on various meteorological conditions such as temperature and PAR.