Re-assessment of hydroxyl radical chemistry using new observation data and model comparisons

Atmospheric formation of ozone and secondary organic aerosols as well as the removal of greenhouse gases such as methane and hydrofluorocarbons depend on the fast radical cycling of the hydroxyl radical (OH). Previous measurements of these radicals in forest environments have shown serious discrepancies with model predictions, bringing into question our understanding of OH radical chemistry, especially in regions characterized by low NOx (NOx = NO + NO2) and high biogenic volatile organic compound (BVOC) concentrations. However, previous studies have discovered that some OH radical measurement techniques may be sensitive to interferences, such as from the ozonolysis of BVOCs. This has the potential to cause artificially high observations of OH especially in forested areas. In this work, we present an analysis of previous measurements of OH radical concentrations from rural, suburban, and urban areas while accounting for the measured interferences and covering a wide range of NOx concentrations. This re-assessment provides insight regarding our current understanding of OH radical recycling under low NOx and high BVOC conditions.