High contributions of fossil fuel sources to char-EC/soot-EC at a high-altitude site: Direct radiative effects and transport pathway

Abstract

Char-EC and soot-EC in the atmosphere produced from different fuel combustion have distinct optical properties which lead to different radiative forcing. Pollutants transported into high-altitude environment could have a long-lasting radiative effect due to being free of deposition. In this study, the mass absorption cross-section (MAC), the sources, transport pathways and the direct radiative effects (DREs) of soot-EC and char-EC were investigated at a peak of Mountain Hua (Mt. Hua) in China. The measurement results showed that soot-EC and char-EC account for 15.7 % and 84.3 % of EC, respectively. The mean MAC (λ = 633 nm) of soot-EC (13.7 ± 3.8 m2/g) was much higher than that of char-EC (5.4 ± 2.5 m2/g), indicating a stronger light absorption ability for soot-EC. During the study period, 62.1 % char-EC was from anthracite chunk coal, 24.3 % of it from liquid fuel combustion. By contrast, 59.0 % soot-EC from liquid fuel combustion and 36.6 % of it from anthracite chunk coal. EC (both char-EC and soot-EC) produced from anthracite chunk coal reached the peak of the Mt. Hua primarily through the raising of the planetary boundary layer (PBL), while the EC produced from liquid fuel arrived the peak mainly by the regional transport above the PBL of the site. Although soot-EC has a stronger ability (2.8 times higher) to absorb the light compared with char-EC, its DRE (5.7 ± 3.9 W m−2) was lower than that of char-EC (11.6 ± 6.9 W m−2) due to the smaller mass quantity. Liquid fuel consumption contributed 3.5 ± 2.9 W m−2 DRE of soot-EC, while the combustion of anthracite chunk coal contributed 7.5 ± 5.7 W m−2 DRE of char-EC. This study highlights the differences in DREs of soot-EC and char-EC from fossil fuel combustion and the DRE mass efficiency of soot-EC and char-EC. The results emphasize the divergent climate warming effects caused by the combustion of different fossil fuels and imply that setting path to a green transition of energy use would benefit reducing the EC perturbation to the radiation balance of earth-atmosphere.