1.3 Seasonal variations in pollution
Winter conditions tend to reduce mixing in the atmosphere because of stronger and more frequent temperature inversions. As a result, pollutants can be trapped in a shallow layer at ground level and concentrated. This is often compounded by still conditions, further limiting dispersion of the pollutants. The seasonal pattern of concentrations for benzene shown in Figure 1 is typical of many of the pollutants in this study.
Figure 1: Annual ambient benzene concentrations (average parts per billion by volume) at Rozelle, Sydney
Other factors may also contribute to higher concentrations in winter for these pollutants. For many compounds produced by motor vehicles, cold starts in winter lead to longer periods of incomplete combustion and longer warm-up times for catalytic converters, which generates more pollution. Pollutants such as PAHs are also more prevalent in winter because of the use of solid fuel heaters at that time of the year.
Page last updated: 26 February 2011