HR: 16:30h
AN: A34B-03 INVITED    [Abstracts]
TI: Day-of-week Effects in Ozone, Nitrogen Oxides, and VOC Reactivity Within and Downwind of Sacramento
AU: * Murphy, J G
EM: jmurphy@chem.utoronto.ca
AF: Department of Chemistry, University of California, Berkeley, CA 94720, United States
AU: * Murphy, J G
EM: jmurphy@chem.utoronto.ca
AF: Department of Chemistry, University of Toronto, Toronto, ON M5S 3H6, Canada
AU: Day, D A
EM: daday@ucdavis.edu
AF: Department of Chemistry, University of California, Berkeley, CA 94720, United States
AU: Day, D A
EM: daday@ucdavis.edu
AF: Land, Air and Water Resources Department, University of California, Davis, CA 95616, United States
AU: Cleary, P A
EM: cleary.patricia@gmail.com
AF: Department of Chemistry, University of California, Berkeley, CA 94720, United States
AU: Cleary, P A
EM: cleary.patricia@gmail.com
AF: Department of Geosciences, University of Wisconsin at Parkside, Kenosha, WI 53141, United States
AU: Wooldridge, P J
EM: pjwool@socrates.berkeley.edu
AF: Department of Chemistry, University of California, Berkeley, CA 94720, United States
AU: Millet, D B
EM: millet@eps.harvard.edu
AF: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, United States
AU: Millet, D B
EM: millet@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, United States
AU: Goldstein, A H
EM: ahg@nature.berkeley.edu
AF: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, United States
AU: Cohen, R C
EM: cohen@cchem.berkeley.edu
AF: Department of Chemistry, University of California, Berkeley, CA 94720, United States
AU: Cohen, R C
EM: cohen@cchem.berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720, United States
AB: Day-of-week patterns in human activities can be used to examine the ways in which differences in primary emissions result in changes in the rates of photochemical reactions, and the production of secondary pollutants. Data from twelve California Air Resources Board monitoring sites in Sacramento, CA, and the downwind Mountain Counties air basin are analyzed to reveal day of week patterns in ozone and its precursors in the summers of 1998-2002. On the weekends, NO_x concentrations drop by 35%, whereas VOC reactivity changes by less than 15%, likely due to significant reductions in diesel truck traffic. The main driver for day-of- week differences in ozone abundance at urban sites is the reduced titration of O₃ by fresh NO emissions on weekends. By analyzing day-of-week patterns in odd oxygen (O₃+NO₂), we can eliminate this complication and focus on the NO_x-dependence of ozone production and the related photochemistry. In the downwind Mountain Counties, ozone production is found to be NO_x-limited, whereas at the urban and suburban sites of Sacramento, ozone production is NO_x-saturated. An analysis of day-of-week cycles in Sacramento reveals that boundary layer chemistry and mixing in of residual air from above both contribute to the observed accumulation of ozone at surface sites. This interpretation is consistent with the day-of-week patterns in a range of VOC with different emission sources and lifetimes and in higher nitrogen oxides that are co-products of ozone. We use isoprene as a probe of local oxidation rates, and infer that on the weekend OH is higher in the urban area and lower at one of the forested Mountain Counties sites, as expected from the NO_x- dependence. Our analysis also demonstrates that in NO_x-saturated environments, gas phase HNO₃, and by extension particulate nitrate, concentrations are relatively insensitive to changes in NO_x emissions.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting