Trends of atmospheric black carbon concentration over the United Kingdom

The continuous observations over a period of 7 years (2009-2016) available at 7 locations show declining trend of atmospheric BC in the UK. Among all the locations, the highest decrease of 8 +/- 3 percent per year was observed at the Marylebone road in London. The detailed analysis performed at 21 locations during 2009-2011 shows that average annual mean atmospheric BC concentration were 0.45 +/- 0.10, 1.47 +/- 0.58, 1.34 +/- 0.31, 1.83 +/- 0.46 and 9.72 +/- 0.78 mu gm(-3) at rural, suburban, urban background, urban centre and kerbside sites respectively. Around 1 mu gm(-3) of atmospheric BC could be attributed to urban emission, whereas traffic contributed up to 8 mu gm(-3) of atmospheric BC near busy roads. Seasonal pattern was also observed at all locations except rural and kerbside location, with maximum concentrations (1.2-4 mu gm(-3)) in winter. Further, minimum concentrations (0.3-1.2 mu gm(-3)) were observed in summer and similar concentrations in spring and fall. At suburban and urban background locations, similar diurnal pattern were observed with atmospheric BC concentration peaks ( approximate to 1.8 mu gm(-3)) in the morning (around 9 a.m.) and evening (7-9 p.m.) rush hours, whereas minimum concentrations were during late night hours (peak at 5 a.m.) and the afternoon hours (peak at 2 p.m.). The urban centre values show a similar morning pattern (peak at 9 a.m.; concentration -2.5 mu gm(-3)) in relation to background locations but only a slight decrease in concentration in the afternoon which remained above 2 mu gm(-3) till midnight. It is concluded that the higher flow of traffic at urban centre locations results in higher atmospheric BC concentrations throughout the day. Comparison of weekday and weekend daily averaged atmospheric BC showed maximum concentrations on Friday, having minimum levels on Sunday. This study will help to refine the atmospheric BC emission inventories and provide data for air pollution and climate change models evaluation, which are used to formulate air pollution mitigation policies.