because emissions are constant throughout the year. However in most
urban, residential and rural areas where the local sources are
related to residential and commercial heating, they show significant
seasonality during the year (e.g., relative enhancement during the
cold winter). This effect is particularly pronounced when the fuels
used for heating exhibit high PAH emissions factors. A clear example
of this is found in Northern Ireland, UK where solid fuel sources such
as coal and wood are still commonly burnt for heating (Brown, 2013;
R.J.C. Brown et al., 2013). For instance, the average BaP concentration
during December–January was 3.0 ng m−3 compared to 0.19 ng m−3
during June–August.