Atmospheric VOC chemistry in forested environments

The importance of biogenic volatile organic compounds (BVOC) with respect to tropospheric ozone chemistry was addressed through the study of isoprene and n-aldehydes. A fast-response chemical ionization/collisionally-activated dissociation quadrupole ion trap method was developed to study the dynamic nighttime disappearance of isoprene. Isoprene measurements were made at the University of Michigan Biological station as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) study. These data, in concert with available OH concentration data and estimates of vertical mixing show the most likely causes for the observed isoprene decay. Concentration data for propanal, pentanal, hexanal, heptanal, octanal, and nonanal were collected at a rural site in Tennessee during the Southern Oxidants Study (SOS) of 1999. The origin of these compounds, found at unexpectedly high concentrations at the SOS site, was not determined due to the lack of a clear biogenic or anthropogenic source. While these species were shown to be significant contributors to OH reactivity, their potential to form sinks for radicals and NOx was also demonstrated through the elucidation of the peroxyacyl nitrate and organic nitrate yields for nonanal. Overall, nonanal, and perhaps other n-aldehydes may actually inhibit ozone production