Evolution of the Magnitude and Spatial Extent of the Weekend Ozone Effect in California's South Coast Air Basin, 1981-2000

• Published in: Journal of the Air & Waste Management Association (1995) Vol. 53; no. 7; pp. 802 - 815
• Main Authors: Fujita, Eric M., Stockwell, William R., Campbell, David E., Keislar, Robert E., Lawson, Douglas R.
• Format: Journal Article
• Language: English
• Published: Pittsburgh, PA Taylor & Francis Group 01.07.2003; Air & Waste Management Association; Air and Waste Management Association; Taylor & Francis Ltd
• Subjects: Air Pollutants - analysis; Air pollution; Applied sciences; Atmospheric ozone; California; Chemical composition and interactions. Ionic interactions and processes; Drinking water and swimming-pool water. Desalination; Earth, ocean, space; Environmental aspects; Exact sciences and technology; External geophysics; Health aspects; Measurement; Meteorology; Nitrogen Oxides - analysis; Organic Chemicals; Oxidants, Photochemical - analysis; Ozone - analysis; Periodicity; Pollution; Volatile organic compounds; Water treatment and pollution; California; INE, USA, California; USA, California, South
• ISSN: 1096-2247; 2162-2906
• DOI: 10.1080/10473289.2003.10466225

Since the mid-1970s, ozone (O 3 ) levels in portions of California's South Coast Air Basin (SoCAB) on weekends have been as high as or higher than levels on weekdays, even though emissions of O 3 precursors are lower on weekends. Analysis of the ambient data indicates that the intensity and spatial extent of the weekend O 3 effect are correlated with day-of-week variations in the extent of O 3 inhibition caused by titration with nitric oxide (NO), reaction of hydroxyl radical (OH) with nitrogen dioxide (NO 2 ), and rates of O 3 accumulation. Lower NO mixing ratios and higher NO 2 /oxides of nitrogen (NO x ) ratios on weekend mornings allow O 3 to begin accumulating approximately an hour earlier on weekends. The weekday/weekend differences in the duration of O 3 accumulation remained relatively constant from 1981 to 2000. In contrast, the rate of O 3 accumulation decreased by one-third to one-half over the same period; the largest reductions occurred in the central basin on weekdays. Trends in mixing ratios of O 3 precursors show a transition to lower volatile organic compound (VOC)/NO x ratios caused by greater reductions in VOC emissions. Reductions in VOC/NO x ratios were greater on weekdays, resulting in higher VOC/NO x ratios on weekends relative to weekdays. Trends in VOC/NO x ratios parallel the downward trend in peak O 3 levels, a shift in the location of peak O 3 from the central to the eastern portion of the basin, and an increase in the magnitude and spatial extent of the weekend O 3 effect.