Nitrate ion photochemistry at interfaces: a new mechanism for oxidation of α-pinene

Yong Yu; Michael J. Ezell; Alla Zelenyuk; Dan Imre; Liz Alexander; John Ortega; Jennie L. Thomas; Karun Gogna; Douglas J. Tobias; Barbara D'Anna; Chris W. Harmon; Stanley N. Johnson; Barbara J. Finlayson-Pitts

doi:10.1039/B719495A

Nitrate ion photochemistry at interfaces: a new mechanism for oxidation of α-pinene

Yong Yu,^a Michael J. Ezell,^a Alla Zelenyuk,^b Dan Imre,^c Liz Alexander,^b John Ortega,^b Jennie L. Thomas,^a Karun Gogna,^a Douglas J. Tobias,^a Barbara D'Anna,^a Chris W. Harmon,^a Stanley N. Johnson^a and Barbara J. Finlayson-Pitts*^a

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^a Department of Chemistry, University of California Irvine, Irvine, USA
E-mail: bjfinlay@uci.edu
Fax: +1 (949) 824-2420
Tel: +1 (949) 824-7670

^b Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, USA

^c Imre Consulting, Richland, USA

Abstract

The photooxidation of 0.6–0.9 ppm α-pinene in the presence of a deliquesced thin film of NaNO₃, and for comparison increasing concentrations of NO₂, was studied in a 100 L Teflon® chamber at relative humidities from 72–88% and temperatures from 296–304 K. The loss of α-pinene and the formation of gaseous products were followed with time using proton transfer mass spectrometry. The yields of gas phase products were smaller in the NaNO₃ experiments than in NO₂ experiments. In addition, pinonic acid, pinic acid, trans-sobrerol and other unidentified products were detected in the extracts of the wall washings only for the NaNO₃ photolysis. These data indicate enhanced loss of α-pinene at the NaNO₃ thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that α-pinene has an affinity for the surface of the deliquesced nitrate thin film, enhancing the opportunity for oxidation of the impinging organic gas during the nitrate photolysis. This new mechanism of oxidation of organics may be partially responsible for the correlation between nitrate and the organic component of particles observed in many field studies, and may also contribute to the missing source of SOA needed to reconcile model predictions and field measurements. In addition, photolysis of nitrate on surfaces in the boundary layer may lead to oxidation of co-adsorbed organics.

Physical Chemistry Chemical Physics

Nitrate ion photochemistry at interfaces: a new mechanism for oxidation of α-pinene

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Nitrate ion photochemistry at interfaces: a new mechanism for oxidation of α-pinene

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