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www.atmos-chem-phys-discuss.net/6/11971/2006/
doi:10.5194/acpd-6-11971-2006
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The weekend effect within and downwind of Sacramento: Part 2. Observational evidence for chemical and dynamical contributions
1University of California at Berkeley, Department of Chemistry, USA
2University of California at Berkeley, Department of Environmental Science, Policy and Management, USA
3University of California at Berkeley, Department of Earth and Planetary Sciences, USA
4now at University of East Anglia, School of Environmental Sciences, UK
5now at University of California at Davis, Land, Air and Water Resources Department, USA
6now at University of Pennsylvania, Department of Chemistry, USA
7now at Harvard University, Department of Earth and Planetary Sciences, USA
Abstract. Observations of day-of-week patterns and diurnal profiles of ozone, volatile organic compounds and nitrogen oxides are examined to assess the chemical and dynamical factors governing the daytime ozone accumulation and the distribution of chemically related species in Central California. Isoprene observations show that urban OH concentrations are higher on the weekend whereas rural OH concentrations are lower on the weekend, confirming that NOx concentrations have a direct effect on the rate of photochemical ozone production and that the transition from NOx-saturated (VOC-limited) to NOx-limited chemistry occurs between the city and the downwind rural counties. We quantify the extent to which mixing of ozone and its precursors from aloft contributes to the daytime accumulation of ozone at the surface in Sacramento. Ozone production in the rural Mountain Counties is currently NOx-limited and will decrease in response to NOx emission reductions in the Sacramento Valley. However, NOx emissions reductions of at least 50% (from weekday levels) are necessary to bring about a significant decrease in accumulation of ozone at the surface in the Sacramento Valley. The impact of NOx emission reductions on the frequency of exceeding the federal 8-hour ozone standard at an individual site will depend on the balance between reduced titration and the sign and magnitude of production changes. We further show that HNO3 production, which depends on the product of OH and NO2 mixing ratios, is a constant at high NOx, suggesting that NOx must be reduced below a threshold before nitrate aerosol can be expected to decrease.
Discussion Paper (PDF, 2392 KB) Interactive Discussion (Closed, 2 Comments) Publication in ACP not foreseen
Citation: Murphy, J. G., Day, D. A., Cleary, P. A., Wooldridge, P. J., Millet, D. B., Goldstein, A. H., and Cohen, R. C.: The weekend effect within and downwind of Sacramento: Part 2. Observational evidence for chemical and dynamical contributions, Atmos. Chem. Phys. Discuss., 6, 11971-12019, doi:10.5194/acpd-6-11971-2006, 2006. Bibtex EndNote Reference Manager XML
