Quantification of fossil and non-fossil sources to the reduction of carbonaceous aerosols in the Yangtze River Delta, China: Insights from radiocarbon analysis during 2014-2019

From 2013, a significant decline in fine particulate matter (PM2.5) occurred in most Chinese cities. In Nanjing, a capital city in the central of the Yangtze River Delta (YRD) region, the mass concentrations of total carbon (TC) in PM2.5 decreased by approximately 48% during wintertime from 2014 to 2019. To provide detailed information in this trend, source apportionment of TC was carried out using a radiocarbon-(C-14-) based method. In general, the average mass concentrations (and fossil fuel proportions) of TC, organic carbon (OC) and elemental carbon (EC) in six winters were 16.3 +/- 8.5 mu g m(-3) (51%), 14.4 +/- 7.8 mu g m(-)(3) (48%) and 2.0 +/- 1.2 mu g m(-3) (65%), respectively. From 2014 to 2019, the reduction in TC was mainly attributed to the decline in non-fossil sources (6.4, 6.3-6.5 mu g m(-3)) rather than fossil-fuel sources (3.6, 3.4-3.7 mu g m(-3)) (medians, 10th-90th percentiles). The reduction of OC (9.1 mu g m(-3)) was mainly attributed to OC from biomass burning (5.3, 4.6-6.1 mu g m(-3)) and secondary formation from fossil-fuel sources (3.3, 2.6-3.9 mu g m(-3)). Although the inter-annual variations for EC were less obvious, the reduction was dominated by the variations in non-fossil emissions (i.e., biomass burning). This study highlights the important role of non-fossil source control in the reduction of TC mass concentration in the YRD. Strategies of future emission control may pay more attention to both biomass burning emissions and secondary organic aerosols from precursors originating from fossil sources.