The hydroxyl radical (OH) is the dominant oxidant in the atmosphere, controlling the lifetimes of volatile organic compounds (VOCs) and contributing to production of ozone and secondary organic aerosols (SOA). Despite its importance, there is significant discrepancy between measured and modeled OH concentrations, particularly in forested regions, bringing into question our understanding of OH sources and sinks. Nitrous acid (HONO) can be a major source of OH, and recent measurements have shown higher than expected concentrations of HONO in remote environments. HONO is produced through a myriad of sources including combustion, heterogeneous and gas-phase reactions, and emission from soil microbiome. Here, we present measurements of HONO and OH from the Manitou Experimental Forest, a ponderosa pine forest in the Front Range of Colorado. Supporting measurements of photolysis rates, VOCs, NOx, and other species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM). The model results will be compared to the OH radical measurements in order to determine the importance of HONO emissions to radical production at this site.

HONO and OH radical chemistry in a ponderosa pine forest: Measurement and model comparisons

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