Carbon isotope seasonal characteristics of fine carbonaceous aerosol in Jinzhong City, Shanxi Province, China

摘要

Stable carbon isotope signatures were observed in organic carbon (OC) and elemental carbon (EC) fractions of fine carbonaceous aerosol (PM2.5) sampled in spring, summer, and winter (December 2013 to August 2014) in Jinzhong in Shanxi Province. The stable carbon isotope composition of EC (delta C-13(EC)) varied from 25.93 parts per thousand to -22.20 parts per thousand during the sampling (mean value of 24.35 +/- 1.11%), with depletion in summer ( 25.44 +/- 0.32 parts per thousand) and enrichment in winter (-23.04 +/- 0.71 parts per thousand). The contribution of vehicle exhaust was 65% in summer, and the contribution of fossil fuel combustion was 92% in winter based on carbon isotope mass balance model. The stable carbon isotope compositions of OC (delta C-13(OC)) over the whole sampling period ranged from -29.75 parts per thousand to -22.87 parts per thousand (mean value of -25.10 +/- 1.47 parts per thousand), with enrichment in winter (-24.12 +/- 0.88 parts per thousand) and depletion in spring (-26.40 +/- 1.50 parts per thousand). Compared with delta C-13(EC), the delta C-13(OC) in spring is depleted in C-13 (Delta C-13(OC-EC) = delta C-13(OC) - delta C-13(EC) = 1.55 parts per thousand) because of the formation of secondary OC (SOC) from the photo-oxidation reactions. Summertime delta C-13(OC) (-24.52 +/- 0.28 parts per thousand) is more positive than delta C-13(EC) because of the strong photochemical aging. The negative value of Delta C-13(OC-EC) in winter may be attributed to a complex set of reasons, including the unfavorable meteorological conditions (e.g., low temperature, low boundary layer height, and frequent temperature inversions), coal combustion, vehicle exhaust, gaseous fuel burning, and SOC formation from photo-oxidation reactions of volatile organic compounds (VOCs) caused by fossil fuel combustion. The seasonal variation of delta C-13(TC) was consistent with that of delta C-13(OC), and the annual average delta C-13(TC) ( 24.80 +/- 1.12%) implicated fossil fuels combustion. This study highlights that the isotope signatures of EC can be used for source apportionment, reveals the strong influence of atmospheric processing on the isotope signature of OC (e.g., SOC formation and photochemical aging), and suggests the potential application of isotope technology in air pollution research.