Characterization of black carbon-containing fine particles in Beijing during wintertime

Abstract

Abstract. Refractory black carbon (BC) is a product of incomplete combustion of fossil\nfuel, biomass and biofuel, etc. By mixing with other species, BC can play\nsignificant roles in climate change, visibility impairment and human health.\nSuch BC-containing particles in densely populated megacities like Beijing may\nhave specific sources and properties that are important to haze formation and\nair quality. In this work, we exclusively characterized the BC-containing\nparticles in urban Beijing by using a laser-only Aerodyne soot particle\naerosol mass spectrometer (SP-AMS), as part of the Atmospheric Pollution &\nHuman Health (APHH) 2016 winter campaign. The average mass ratio of coating\nto BC core ( RBC) was found to be ∼5.0 . Positive matrix\nfactorization shows the presence of significant primary fossil fuel and\nbiomass-burning organics (64\u2009% of total organics). Yet secondary species,\nincluding sulfate, nitrate and oxygenated organic aerosol (OA) species, could\nhave significant impacts on the properties of BC-containing particles,\nespecially for ones with larger BC core sizes and thicker coatings. Analyses\nof sources and diurnal cycles of organic coating reveal significant afternoon\nphotochemical production of secondary OA (SOA), as well as nighttime aqueous\nproduction of a portion of highly oxygenated OA. Besides SOA, photochemical\nproduction of nitrate, not sulfate, appeared to be important. Further\ninvestigations on BC-containing particles during different periods show that,\non average, more polluted periods would have more contributions from\nsecondary species and more thickly coated BC tended to associate with more\nsecondary species, indicating the important role of chemical aging to the\npollution of BC-containing particles in urban Beijing during wintertime.\nHowever, for individual pollution events, primary species (fossil fuel, coal\nand biomass-burning emissions) could also play a dominant role, as revealed\nby the compositions of BC-containing particles in two polluted episodes during the\nsampling period.