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

  • Author(s): Yu, Yong
  • Ezell, Michael J
  • Zelenyuk, Alla
  • Imre, Dan
  • Alexander, Liz
  • Ortega, John
  • Thomas, Jennie L
  • Gogna, Karun
  • Tobias, Douglas J
  • D'Anna, Barbara
  • Harmon, Chris W
  • Johnson, Stanley N
  • Finlayson-Pitts, Barbara J
  • et al.
Abstract

The photooxidation of 0.6-0.9 ppm alpha-pinene in the presence of a deliquesced thin film of NaNO(3), and for comparison increasing concentrations of NO(2), was studied in a 100 L Teflon(R) chamber at relative humidities from 72-88% and temperatures from 296-304 K. The loss of alpha-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 NaNO(3) experiments than in NO(2) 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 NaNO(3) photolysis. These data indicate enhanced loss of alpha-pinene at the NaNO(3) thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that alpha-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.

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