Besides emissions, there are other factors that can contribute to high
concentrations of PAHs during winter (EPA, 2001). During cold months
there is less mixing in the atmosphere because of stronger and more frequent
temperatures inversions. As result, pollutants remain trapped in a
surface layer at ground level,which is often intensified by the calm conditions,
limiting even further the dispersion of pollutants. In contrast,
during the period of warmer months, temperatures inversions are less
frequent and higher increased photochemical oxidation are favourable
to PAHs decreasing in ambient air (Liu et al., 2007), reaching the values
considered minimal during this period