References

ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

Atmos. Chem. Phys. Discuss.

1680-7375

Göttingen, Germany

10.5194/acpd-9-13123-2009

Evidence of the water-cage effect on the photolysis of NO3- and FeOH2+, and its implications for the photochemistry at the air-water interface of atmospheric droplets

Nissenson

¹ Dabdub

¹ Das

² ³ Maurino

² Minero

² Vione

Dept. of Mechanical and Aerospace Engineering, University of California, Irvine, CA, USA

Dipartimento di Chimica Analitica, Università degli Studi di Torino, Via P. Giuria 5, 10125 Torino, Italy

Dept. of Chemical Engineering, Haldia Institute of Technology, ICARE complex, Haldia 721657, India

12 06 2009

9 3 13123 13153

2009

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://acp.copernicus.org/preprints/9/13123/2009/acpd-9-13123-2009.html

The full text article is available as a PDF file from https://acp.copernicus.org/preprints/9/13123/2009/acpd-9-13123-2009.pdf

Experiments are conducted to determine the photolysis quantum yields of nitrate, FeOH2+, and H2O2 in the bulk and at the surface layer of water. Results show that the quantum yields of nitrate and FeOH2+ are enhanced at the surface compared to the bulk due to a reduced water-cage surrounding the photo-fragments (•OH+•NO2 and Fe2++•OH, respectively). However, no evidence is found for an enhanced quantum yield for H2O2 at the surface. The photolysis rate constant distribution within nitrate, FeOH2+, and H2O2 aerosols is calculated by combining the quantum yield data with Mie theory calculations of light intensity. Values for the photolysis rate constant of nitrate and FeOH2+ are significantly higher at the surface than in the bulk due to enhanced quantum yields at the surface. The results concerning the rates of photolysis of these photoactive species are applied to the assessment of the reaction between benzene and •OH in the presence of •OH scavengers in an atmospherically relevant scenario. For a droplet of 1μm radius, a large fraction of the total •OH-benzene reaction (15% for H2O2, 20% for nitrate, and 35% for FeOH2+) occurs in the surface layer, which accounts for just 0.15% of the droplet volume. By neglecting the surface effects on photochemistry, the rate of the important reactions could be underestimated by a considerable amount.

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