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Issue 3, 2017
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OH production from the photolysis of isoprene-derived peroxy radicals: cross-sections, quantum yields and atmospheric implications

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Abstract

In environments with high concentrations of biogenic volatile organic compounds and low concentrations of nitrogen oxides (NOx = NO + NO2), significant discrepancies have been found between measured and modeled concentrations of hydroxyl radical (OH). The photolysis of peroxy radicals from isoprene (HO-Iso-O2) 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 (σRO2,OH) from the photolysis of HO-Iso-O2 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-O2. Values of σRO2,OH for HO-Iso-O2 ranged from (6.0 ± 1.6) × 10−20 cm2 molecule−1 at 310 nm to (0.50 ± 0.15) × 10−20 cm2 molecule−1 at 362.5 nm. OH photodissociation yields from HO-Iso-O2 photolysis, ϕOH,RO2, were determined via comparison of the measured values of σRO2,OH to the total absorption cross-sections for HO-Iso-O2 (σRO2), which were obtained using a newly-constructed spectrometer. ϕOH,RO2 was determined to be 0.13 ± 0.04 at wavelengths from 310–362.5 nm. To determine the impact of HO-Iso-O2 photolysis on atmospheric OH concentrations, a modeling case-study for a high-isoprene, low-NOx 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-O2 photolysis in the model had increased the OH concentration by only 1% on average from 10:00–16:00 local time. Thus, HO-Iso-O2 photolysis alone is insufficient to resolve the discrepancy seen between measured OH concentrations and those predicted by atmospheric chemistry models in such environments.

Graphical abstract: OH production from the photolysis of isoprene-derived peroxy radicals: cross-sections, quantum yields and atmospheric implications

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Publication details

The article was received on 30 Sep 2016, accepted on 12 Dec 2016 and first published on 12 Dec 2016


Article type: Paper
DOI: 10.1039/C6CP06718B
Citation: Phys. Chem. Chem. Phys., 2017,19, 2332-2345
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    OH production from the photolysis of isoprene-derived peroxy radicals: cross-sections, quantum yields and atmospheric implications

    R. F. Hansen, T. R. Lewis, L. Graham, L. K. Whalley, P. W. Seakins, D. E. Heard and M. A. Blitz, Phys. Chem. Chem. Phys., 2017, 19, 2332
    DOI: 10.1039/C6CP06718B

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