4.2 Seasonal concentrations of pollution
The focus of the EPA study was to sample during winter when conditions are conducive to higher levels of many pollutants. Some data was also collected in other seasons to test the hypothesis that PAH levels peaked in winter. Several factors contribute to higher concentrations of PAHs in winter:
- There is less 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. This is often compounded by still conditions, further limiting dispersion of pollutants.
- The use of solid fuel heaters in winter adds to overall emissions.
Page last updated: 26 February 2011