Characteristics and sources of carbonaceous aerosol across urban and rural sites in a rapidly urbanized but low-level industrialized city in the Sichuan Basin, China

Organic carbon (OC) and elemental carbon (EC) were measured in 24 h fine particulate matter (PM 2.5 ) samples collected from May 2015 to April 2016 at urban and rural sites in Nanchong, a rapidly urbanized but low-level industrialized city in the Sichuan Basin, China. The annual average PM 2.5 , OC, and EC concentrations at urban sites were 45.6–55.7, 8.5–11.5, and 2.8–3.4 μg m −3 , respectively, which were similar to the corresponding values (48.3, 10.6, and 3.3 μg m −3 ) at the rural site. The PM 2.5 concentrations displayed strong monthly variations, with the highest (78.8–105.0 μg m −3 ) in January or February. Likewise, daily OC and EC concentrations exhibited high values in October (only for OC) and December 2015 to February 2016. Correlation, positive matrix factorization, and concentration weighted trajectory analyses were combined to investigate the sources of carbonaceous aerosol. The results indicated that OC and EC were mainly from biomass burning (60.7% and 45.8%) and coal combustion (30.2% and 25.7%), followed by vehicle emissions and road dust. The enhanced emissions from residential coal and biofuel uses in winter and straw combustion in October contributed to higher concentrations of OC and EC during these months. The contributions of biomass burning to OC and EC were significantly higher at the rural site (69.2% and 51.8%) than urban sites (56.3–58.6% and 37.8–41.5%). In addition to local emissions, the high concentrations of OC and EC at Nanchong were also influenced by regional transport in the basin.