Total OH reactivity measurements in laboratory studies of the photooxidation of isoprene

Abstract

The hydroxyl radical (OH) is the principal oxidizing agent in Earth's troposphere. Measurements of the total OH reactivity, defined as the reciprocal of the lifetime of OH, have been employed in field studies to estimate the entire amount of reactive trace gases in the atmosphere. Here, the OH reactivity technique has been employed in laboratory studies of the OH initiated atmospheric oxidation of the important biogenic volatile organic compound, isoprene. A significant discrepancy was observed between measured and calculated OH reactivity, indicating that OH was reacting with some oxidation products not measured in the experiment. The “missing” OH reactivity gradually increased as the oxidation progressed and contributed up to 40% of the total OH reactivity. In the presence of NO, the “missing” OH reactivity is likely due to a number of first-generation products produced in low yields, while in the absence of NO, alternative pathways that produce less reactive products are also occurring.This work demonstrates that OH reactivity measurements can be successfully incorporated into atmospheric simulation chamber studies of VOC degradation. The OH reactivity technique has the potential to be a powerful tool for elucidating finer details of VOC oxidation.