The Behavior of the Hydroxyl and Hydroperoxyl Radicals During PROPHET2000

Biogenic emissions strongly influence the behavior of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) in a forest that is distant from urban areas. The mixing ratios of OH and HO2 and the OH reactivity were measured as part of the multi-investigator study, PROPHET2000, which took place on a tower above a forest at the University of Michigan Biological Station near Pellston Michigan in June and July 2000. Both OH and HO2 showed strong diurnal variations, although observed HO2 and especially observed OH were greater that expected at night. The observed OH reactivity was highly variable from day to day, with values ranging from greater than 20 s-1 during some more polluted days to less than 2 s-1 on some nights. This diurnal variation, where observed OH reactivity was greater during the day, was not seen in Nashville in summer 1999, where observed OH reactivity tended to be slightly greater during the night. The observed OH, HO2, and OH reactivity all appear to correlate with O3 and temperature, both day and night. The implications of these observations will be discussed.