LAUSR

Abstract There is an increasing scientific interest in carbonaceous aerosols due to their effects on local air quality and climate. The database of the UK air monitoring networks from 2009 to 2017 was analyzed to examine the trends in black carbon (BC), brown carbon (BrC), elemental carbon (EC) and organic carbon (OC) at 11 sites with different classifications over the UK. The concentrations increased from rural to urban background to kerbside sites. BC showed the strongest variation, with maxima at kerbside (>9.0 μg m−3) and minima at rural sites (below 1.0 μg m−3). On the other hand, BrC showed no clear variation according to site classification. BrC increased as domestic emissions of wood smoke increased at weekends. Total OC and secondary OC showed a winter maximum at urban and kerbside sites, while BC increased during the winter at urban sites and in autumn at kerbside sites. Secondary Organic Carbon is dominated by regional transport processes. All pollutants revealed a decreasing long-term trend in the UK, the most significant reduction was observed in BC levels, particularly at the kerbside site (−0.87 μg m−3 yr−1), with lesser rates of decline (−0.08 to −0.13 μg m−3 yr−1) at urban background sites. The general behaviour of BrC was consistent with a major contribution from regional transport. As expected, EC shows similar behaviour to BC, and OC/EC ratios have increased with time as diesel particle filters have reduced EC emissions more than OC, and other sources of primary OC have not changed markedly.