Insights into hydroxyl measurements and atmospheric oxidation in a California forest
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Abstract. The understanding of oxidation in forest atmospheres is being challenged by measurements of unexpectedly large amounts of hydroxyl (OH). A significant number of these OH measurements were made by laser-induced fluorescence in low-pressure detection chambers (called Fluorescence Assay with Gas Expansion (FAGE)) using the Penn State Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). We deployed a new chemical removal method to measure OH in parallel with the traditional FAGE method. The new method gives on average only 4050% of the OH from the traditional method and this discrepancy is temperature-dependent. Evidence indicates that the new method measures atmospheric OH while the traditional method is affected by internally generated OH, possibly from oxidation of biogenic volatile organic compounds. The agreement between OH measured by this new technique and modeled OH suggests that oxidation chemistry in at least one forest atmosphere is better understood than previously thought.
