ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-483-2005 Measurements of N<sub>2</sub>O<sub>5</sub>, NO<sub>2</sub>, and O<sub>3</sub> east of the San Francisco Bay Wood E. C. 1 Bertram T. H. 1 Wooldridge P. J. 1 Cohen R. C. 1 2 3 Department of Chemistry, University of California, Berkeley, California Department of Earth and Planetary Sciences, University of California, Berkeley, California Energy and Environment Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 15 02 2005 5 2 483 491 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/5/483/2005/acp-5-483-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/483/2005/acp-5-483-2005.pdf

We report in situ measurements of N<sub>2</sub>O<sub>5</sub>, NO<sub>2</sub>, and O<sub>3</sub> in Contra Costa County, California during January 2004. Mixing ratios of N<sub>2</sub>O<sub>5</sub>, an intermediate compound in the atmosphere's nocturnal cleansing process, ranged up to 200pmol/mol at night. The highest N<sub>2</sub>O<sub>5</sub> concentrations were correlated with low O<sub>3</sub> and high NO<sub>2</sub> concentrations. The calculated steady state lifetime for N<sub>2</sub>O<sub>5</sub> ranged from 5 to 30min. The total HNO<sub>3</sub> produced by N<sub>2</sub>O<sub>5</sub> hydrolysis over a 14h night was comparable to ambient NO<sub>2</sub> concentrations, and is estimated to be a factor of nine bigger than the HNO<sub>3</sub> produced during the day.