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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.

Introduction: Levoglucosan and carbonaceous species in the background aerosol of coastal southeast China were measured at Jianfengling (JFL), a background mountain site in a National Reserve Park on Hainan Island, and at Hok Tsui (HT), a rural site on the southern coast of Hong Kong from April to May of 2004 during an intensive field study. Methods: We integrated the information from field study, satellite and backward trajectory model to examine the long-range transport of biomass burning smoke from the Philippines and assess its impact on background aerosol in coastal southeast China. Results and discussion: The average levoglucosan concentrations were 42 and 30 ng m at JFL and HT, respectively, while the organic and elemental carbon concentrations were 3.1 and 0.4 μg C m respectively at JFL, and 4.1 and 1.3 μg C m respectively at HT. Elevated levoglucosan concentrations of 85-106 ng m (250-340% extra loadings) at JFL and 57 ng m (170% extra loading) at HT were observed during transport events in which air masses originated from the Philippines. Fire hot spot counts and aerosol index derived from satellite data showed that the spread of biomass burning smoke from the Philippines resulted in large-scale dense aerosol clouds in the adjacent South China Sea and the western Pacific Ocean. The observed high ratio of two biomass-burning tracers (levoglucosan to mannosan) at JFL (7-36) and HT (27) indicated that the biomass smoke originating from the Philippines had significant contributions from open-field burning of agricultural residues, such as rice straw. The pollution plumes were transported to southeast China resulting in elevated concentrations of carbonaceous aerosol and levoglucosan in particular. Using a simplified receptor-based approach, biomass smoke aerosol was estimated to account for 16-28% of OC in the background atmosphere of Hainan and 4.9% of OC at the rural site of Hong Kong during these episode cases, indicating that biomass burning smoke generated in the Philippines could have a significant contribution to background ambient aerosol of southeast coastal China. [ABSTRACT FROM AUTHOR]

Carbonaceous matter is a major constituent in urban aerosols, especially in those collected in China. The size distributions of elemental carbon (EC) and organic carbon (OC) in the range of 0.01-18 µm were measured in an urban location in Guangzhou, China in July 2006. The EC size distribution in the accumulation-mode size was characterized by three significant modes with mass median aerodynamic diameters (MMAD) of ~0.15 µm, ~0.40 µm, and ~0.90 µm, with the second one being the most prominent and accounting for approximately half of the total EC mass. The coexistence of the first two accumulation modes in Guangzhou's urban atmosphere could be explained to be a result of emissions from vehicles operating at different loadings. The dominance of the EC accumulation mode at ~0.40 µm has not often been reported in studies conducted in developed countries, but this observation is consistent with EC size distributions measured in a roadway tunnel in this region. This information is important when modeling the role of EC in modulating the radiative balance and investigating the health effects of EC. The third accumulation mode was postulated to be a result of in-cloud processing after emission. OC had the same size modes as EC but different mass distributions among the modes. The carbonaceous materials in the nucleation mode were dominated by OC. Among particles in the accumulation size range, the OC/EC ratio was higher in the third accumulation mode (MMAD: 0.90 µm) than in the first two accumulation modes, suggesting that in-cloud processing was an important pathway for accumulating OC mass during atmospheric processing of EC particles. [ABSTRACT FROM AUTHOR]