Measurement report: Source apportionment of carbonaceous aerosol using dual-carbon isotopes (C-13 and C-14) and levoglucosan in three northern Chinese cities during 2018-2019

To investigate the characteristics and changes in the sources of carbonaceous aerosols in northern Chinese cities after the implementation of the Action Plan for Air Pollution Prevention and Control in 2013, we collected PM2.5 samples from three representative inland cities, i.e., Beijing (BJ), Xi'an (XA), and Linfen (LF), from January 2018 to April 2019. Elemental carbon (EC), organic carbon (OC), levoglucosan, stable carbon isotope, and radiocarbon were measured in PM2.5 to quantify the sources of carbonaceous aerosol, combined with Latin hypercube sampling. The best estimate of source apportionment showed that the emissions from liquid fossil fuels contributed 29.3 +/- 12.7 %, 24.9 +/- 18.0 %, and 20.9 +/- 12.3% of the total carbon (TC) in BJ, XA, and LF, respectively, whereas coal combustion contributed 15.5 +/- 8.8 %, 20.9 +/- 18.0 %, and 42.9 +/- 19.4 %, respectively. Non-fossil sources accounted for 55 +/- 11 %, 54 +/- 10 %, and 36 +/- 14% of the TC in BJ, XA, and LF, respectively. In XA, 44.8 +/- 26.8% of non-fossil sources were attributed to biomass burning. The highest contributors to OC in LF and XA were fossil sources (74.2 +/- 9.6% and 43.2 +/- 10.8 %, respectively), whereas those in BJ were non-fossil sources (66.8 +/- 13.9 %). The main contributors to EC were fossil sources, accounting for 91.4 +/- 7.5 %, 66.8 +/- 23.8 %, and 88.4 +/- 10.8% in BJ, XA, and LF, respectively. The decline (6 %-16 %) in fossil source contributions in BJ since the implementation of the Action Plan indicates the effectiveness of air quality management. We suggest that specific measures targeted at coal combustion, biomass burning, and vehicle emissions in different cities should be strengthened in the future.