Abstract
Weekend ozone effect studied over a tropical rural and urban site in India shows higher ozone (O3) concentration on weekend compared to weekday. The weekend ozone effect was observed mostly during the summer and winter at the urban, and during summer season at the rural site. Decreased NOx emissions combined with VOC sensitivity on weekends appears to be the possible cause of the weekend ozone effect. The NOx concentration was low on weekend due to reduced commuter vehicular traffic emission. The results indicate nonlinear behavior in the chemistry of O3 production over the tropical region.
Highlights
A phenomenon of higher ozone (O3) concentration on weekend (Saturday to Sunday) compared to weekday (Monday to Friday) is referred to as the “weekend ozone effect,” despite the lower emission of anthropogenic precursor gases on weekend
Ozone concentration over the Indian region depends on photochemical production of O3 related mainly to nitrogen oxides (NOx) concentration
Commuter vehicle is the major source of NOx emission at the urban site, where it is assumed that weekend traffic density is lower than on weekdays
Summary
A phenomenon of higher ozone (O3) concentration on weekend (Saturday to Sunday) compared to weekday (Monday to Friday) is referred to as the “weekend ozone effect,” despite the lower emission of anthropogenic precursor gases on weekend. Altshuler et al (1995) suggested that different dropped rates for NOx and VOC emission on weekend is a major cause of the weekend O3 effect in California. Dreher and Harley (1998) considered that different heavy-duty diesel truck activity on highways between weekdays and weekends caused different reductions for NOx and VOC responsible for weekend O3 effect. Marr and Harley (2002a, b) proposed that less absorption of sunlight due to lower fine-particle concentrations on weekend, resulting in enhanced ozone formation, might be a cause for the weekend ozone effect. The weekend O3 effect has been observed over mid- and high-latitude environments containing mostly nitrogen oxides (NOx), NOx-saturated or volatile organic compounds (VOC), VOC-sensitive (Blanchard and Fairley, 2001; Beaney and Gough, 2002; Marr and Harley, 2002; Qin et al, 2004). Altshuler et al (1995) suggested that different dropped rates for NOx and VOC emission on weekend is a major cause of the weekend O3 effect in California. Dreher and Harley (1998) considered that different heavy-duty diesel truck activity on highways between weekdays and weekends caused different reductions for NOx and VOC responsible for weekend O3 effect. Vukovich (2000) proposed that a larger amount of previous-day carryover ozone was responsible for the higher weekend ozone. Marr and Harley (2002a, b) proposed that less absorption of sunlight due to lower fine-particle concentrations on weekend, resulting in enhanced ozone formation, might be a cause for the weekend ozone effect. Qin et al (2004) suggested that VOC sensitivity combined with a decrease of NOx emissions on weekend was a cause
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