Abstract
Abstract. Several previous field studies have reported unexpectedly large concentrations of hydroxyl and hydroperoxyl radicals (OH and HO2, respectively) in forested environments that could not be explained by the traditional oxidation mechanisms that largely underestimated the observations. These environments were characterized by large concentrations of biogenic volatile organic compounds (BVOC) and low nitrogen oxide concentration. In isoprene-dominated environments, models developed to simulate atmospheric photochemistry generally underestimated the observed OH radical concentrations. In contrast, HO2 radical concentration showed large discrepancies with model simulations mainly in non-isoprene-dominated forested environments. An abundant BVOC emitted by lodgepole and ponderosa pines is 2-methyl-3-butene-2-ol (MBO), observed in large concentrations for studies where the HO2 concentration was poorly described by model simulations. In this work, the photooxidation of MBO by OH was investigated for NO concentrations lower than 200 pptv in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich. Measurements of OH and HO2 radicals, OH reactivity (kOH), MBO, OH precursors, and organic products (acetone and formaldehyde) were used to test our current understanding of the OH-oxidation mechanisms for MBO by comparing measurements with model calculations. All the measured trace gases agreed well with the model results (within 15 %) indicating a well understood mechanism for the MBO oxidation by OH. Therefore, the oxidation of MBO cannot contribute to reconciling the unexplained high OH and HO2 radical concentrations found in previous field studies.
Highlights
The hydroxyl radical (OH) is the most important daytime oxidant in the troposphere and its concentration affects the fate of many pollutants having a direct impact on the formation of ozone (O3) and oxygenated volatile organic compounds (OVOCs), and as such influencing particle formation and climate
Measurements of OH radicals in environments characterized by low nitrogen oxide (NO) concentrations, pristine conditions, and isoprene being the most abundantly measured biogenic volatile organic compound
The MBO decays due to its reaction with OH radicals were slightly overpredicted by the model in accordance with the measured decline of OH reactivity
Summary
The hydroxyl radical (OH) is the most important daytime oxidant in the troposphere and its concentration affects the fate of many pollutants having a direct impact on the formation of ozone (O3) and oxygenated volatile organic compounds (OVOCs), and as such influencing particle formation and climate. Chamber and laboratory studies on methacrolein (Crounse et al, 2012; Fuchs et al, 2014), methyl vinyl ketone (MVK; Praske et al, 2015), isoprene hydroxy hydroperoxide (D’Ambro et al, 2017), and glyoxal (Feierabend et al, 2008; Lockhart et al, 2013) – important products from the oxidation of isoprene by OH – have shown new OH recycling paths as predicted by theory (Peeters et al, 2009; da Silva, 2010, 2012; Setokuchi, 2011). Further laboratory studies have discovered OH radical recycling in the bimolecular reaction of HO2 with acyl peroxy radicals which was previously considered to be a radical termination reaction only (Dillon and Crowley, 2008; Groß et al, 2014; Praske et al, 2015) These results underline the need to carefully investigate the OH radical budget, at least for the most abundant volatile organic compounds (VOCs), to test our current knowledge
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
