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Phys Chem Chem Phys

Title:		"OH production from the photolysis of isoprene-derived peroxy radicals: cross-sections, quantum yields and atmospheric implications"
Author(s):		Hansen RF; Lewis TR; Graham L; Whalley LK; Seakins PW; Heard DE; Blitz MA;
Address:		"School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK. m.blitz@leeds.ac.uk. School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK. m.blitz@leeds.ac.uk and National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK"
Journal Title:		Phys Chem Chem Phys
Year:		2017
Volume:		19
Issue:		3
Page Number:		2332 - 2345
DOI:		10.1039/c6cp06718b
ISSN/ISBN:		1463-9084 (Electronic) 1463-9076 (Linking)
Abstract:		"In environments with high concentrations of biogenic volatile organic compounds and low concentrations of nitrogen oxides (NO(x) = NO + NO(2)), significant discrepancies have been found between measured and modeled concentrations of hydroxyl radical (OH). The photolysis of peroxy radicals from isoprene (HO-Iso-O(2)) in the near ultraviolet represents a potential source of OH in these environments, yet has not been considered in atmospheric models. This paper presents measurements of the absorption cross-sections for OH formation (sigma(RO(2),OH)) from the photolysis of HO-Iso-O(2) at wavelengths from 310-362.5 nm, via direct observation by laser-induced fluorescence of the additional OH produced following laser photolysis of HO-Iso-O(2). Values of sigma(RO(2),OH) for HO-Iso-O(2) ranged from (6.0 +/- 1.6) x 10(-20) cm(2) molecule(-1) at 310 nm to (0.50 +/- 0.15) x 10(-20) cm(2) molecule(-1) at 362.5 nm. OH photodissociation yields from HO-Iso-O(2) photolysis, varphi(OH,RO(2)), were determined via comparison of the measured values of sigma(RO(2),OH) to the total absorption cross-sections for HO-Iso-O(2) (sigma(RO(2))), which were obtained using a newly-constructed spectrometer. varphi(OH,RO(2)) was determined to be 0.13 +/- 0.04 at wavelengths from 310-362.5 nm. To determine the impact of HO-Iso-O(2) photolysis on atmospheric OH concentrations, a modeling case-study for a high-isoprene, low-NO(x) environment (namely, the 2008 Oxidant and Particle Photochemical Processes above a South-East Asian Tropical Rainforest (OP-3) field campaign, conducted in Borneo) was undertaken using the detailed Master Chemical Mechanism. The model calculated that the inclusion of HO-Iso-O(2) photolysis in the model had increased the OH concentration by only 1% on average from 10:00-16:00 local time. Thus, HO-Iso-O(2) photolysis alone is insufficient to resolve the discrepancy seen between measured OH concentrations and those predicted by atmospheric chemistry models in such environments"
Keywords:
Notes:		"PubMed-not-MEDLINEHansen, Robert F Lewis, Tom R Graham, Lee Whalley, Lisa K Seakins, Paul W Heard, Dwayne E Blitz, Mark A eng England 2017/01/06 Phys Chem Chem Phys. 2017 Jan 18; 19(3):2332-2345. doi: 10.1039/c6cp06718b"