Nighttime emission rates

The distinction between primary and secondary pollutants is conceptually useful, because primary and secondary species usually show distinctly different patterns of diurnal and seasonal variation in polluted regions of the atmosphere. The ambient concentrations of primary species are controlled largely by proximity to emission sources and rates of dispersion. The highest concentrations of these species tend to occur at nighttime or early morning and in winter in northerly locations, because atmospheric dispersion rates are slowest at these times. By contrast, high concentrations of... 

Combining the rate coefficients for reactions with OH and NO3 radicals and O3, with daytime average [OH] = 2.5 x 10, nighttime polluted urban area [NO3] = 3 x 10, and a diurnal average [O3] = 10 molecule cm concentrations gives estimates of 1.4 h, 0.4 h, and 5 h for the lifetimes of cw-3-hexenyl acetate with respect to reaction with OH and NO3 radicals and O3, respectively. CM-3-Hexenyl acetate has a short atmospheric lifetime and will be oxidized close to its emission sources. 

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