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. Several previous field studies have reported unexpectedly largeconcentrations of hydroxyl and hydroperoxyl radicals (OH and HO2 ,respectively) in forested environments that could not be explained by thetraditional oxidation mechanisms that largely underestimated theobservations. These environments were characterized by large concentrationsof biogenic volatile organic compounds (BVOC) and low nitrogen oxideconcentration. In isoprene-dominated environments, models developed tosimulate atmospheric photochemistry generally underestimated the observed OHradical concentrations. In contrast, HO2 radical concentrationshowed large discrepancies with model simulations mainly in non-isoprene-dominatedforested environments. An abundant BVOC emitted by lodgepole andponderosa pines is 2-methyl-3-butene-2-ol (MBO), observed in largeconcentrations for studies where the HO2 concentration was poorlydescribed by model simulations. In this work, the photooxidation of MBO by OHwas investigated for NO concentrations lower than 200 pptv in theatmospheric simulation chamber SAPHIR at Forschungszentrum Julich.Measurements of OH and HO2 radicals, OH reactivity ( kOH ),MBO, OH precursors, and organic products (acetone and formaldehyde) were usedto test our current understanding of the OH-oxidation mechanisms for MBO bycomparing measurements with model calculations. All the measured trace gasesagreed well with the model results (within 15 %) indicating a wellunderstood mechanism for the MBO oxidation by OH. Therefore, the oxidation ofMBO cannot contribute to reconciling the unexplained high OH and HO2 radical concentrations found in previous field studies.

atmospheric chemistry and physics

Evaluation of OH and HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations and their budgets during photooxidation of 2-methyl-3-butene-2-ol (MBO) in the atmospheric simulation chamber SAPHIR