The weekend effect within and downwind of Sacramento – Part 1: Observations of ozone, nitrogen oxides, and VOC reactivity

[摘要] Day-of-week patterns in human activities can be used to examine the ways inwhich differences in primary emissions result in changes in the rates ofphotochemical reactions, and the production of secondary pollutants. Datafrom twelve California Air Resources Board monitoring sites in Sacramento,CA, and the downwind Mountain Counties air basin are analyzed to reveal dayof week patterns in ozone and its precursors in the summers of 1998–2002.Measurements of non-methane hydrocarbons are available for the summers of2001–2003 at three of these sites and NO_x at six of these sites for thefull time period. This routine monitoring data is complemented by data setsof ozone and nitrogen oxide concentrations obtained in the summers of 2001and 2003 at three sites in the region and comprehensive measurements of VOCreactivity at two sites in 2001. Daytime concentrations of nitrogen oxides(NO_x≡NO+NO₂) are approximately 35% lower onweekends at all the sites, whereas the VOC reactivity changes by less than10%. All six sites in the Sacramento Valley have higher 8-h maximumaverage ozone on the weekend and are more likely to exceed the nationalstandard of 85 ppb on the weekend. In contrast, all the sites in theMountain Counties are less likely to exceed the federal ozone standard onthe weekend. Analysis of the day-of-week trends in odd oxygen show that theweekend effect of ozone within Sacramento is strongly influenced by NOsources close to the monitoring sites. This suggests that ozone measurementsfrom monitoring sites close to highways, including two rural locations, maynot be representative of the regional abundance, and lead to underestimatesof long term exposure for humans and ecosystems.

[学科分类] 大气科学