Comparative receptor modelling for the sources of fine particulate matter (PM2.5) at urban sites in the UK

The concentration of fine particulate matter (PM2.5) in the UK has been decreasing in the last few decades but remains the leading environmental health risk. As a consequence of changing population, behaviour, activity factors, emissions and regulation, it is likely that the sources of PM2.5 in the UK are changing but a quantitative source apportionment has not been reported for many years. This study analyses the characteristics and sources of PM2.5 collected in 2021 and 2022 at two urban background sites: Birmingham Air Quality Supersite (BAQS) and Ladywood (LW) in Birmingham. Results indicate a notable decrease in the contribution (concentration) of (NH4)2SO4 to PM2.5 from 25% (2.9 μg m− 3) in 2007 to 15% (1.5 μg m− 3) in 2022. In contrast, the contribution of NH4NO3 (20–22%) to PM2.5 remains consistent with that in 2007, despite various air quality actions implemented over the years. These shifts are attributed to changes in SO2 and NOx emissions, coupled with relatively stable NH3 levels—key precursors for (NH4)2SO4 and NH4NO3, which altered the formation dynamics of these compounds, ultimately affecting their contribution to PM2.5 concentrations. Positive matrix factorization (PMF) analysis showed that biomass burning factors (25%), resuspended dust and traffic-related emissions (22%), and secondary aerosols (25%) are the major contributors to PM2.5 mass. Furthermore, PMF and Aethalometer-model analyses consistently showed that biomass burning aerosol concentrations are approximately seven times higher (1.5 μg m− 3) than those observed in studies from 2008 to 2010. These findings suggest that targeted measures to reduce wood burning and road traffic have the greatest potential to reduce PM2.5-related health risks in the West Midland region.