Abstract
Abstract. Refractory black carbon (BC) is a product of incomplete combustion of fossil fuel, biomass and biofuel, etc. By mixing with other species, BC can play significant roles in climate change, visibility impairment and human health. Such BC-containing particles in densely populated megacities like Beijing may have specific sources and properties that are important to haze formation and air quality. In this work, we exclusively characterized the BC-containing particles in urban Beijing by using a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS), as part of the Atmospheric Pollution & Human Health (APHH) 2016 winter campaign. The average mass ratio of coating to BC core (RBC) was found to be ∼5.0. Positive matrix factorization shows the presence of significant primary fossil fuel and biomass-burning organics (64 % of total organics). Yet secondary species, including sulfate, nitrate and oxygenated organic aerosol (OA) species, could have significant impacts on the properties of BC-containing particles, especially for ones with larger BC core sizes and thicker coatings. Analyses of sources and diurnal cycles of organic coating reveal significant afternoon photochemical production of secondary OA (SOA), as well as nighttime aqueous production of a portion of highly oxygenated OA. Besides SOA, photochemical production of nitrate, not sulfate, appeared to be important. Further investigations on BC-containing particles during different periods show that, on average, more polluted periods would have more contributions from secondary species and more thickly coated BC tended to associate with more secondary species, indicating the important role of chemical aging to the pollution of BC-containing particles in urban Beijing during wintertime. However, for individual pollution events, primary species (fossil fuel, coal and biomass-burning emissions) could also play a dominant role, as revealed by the compositions of BC-containing particles in two polluted episodes during the sampling period.
Highlights
Black carbon (BC) is generated from incomplete combustion of carbon-based fuels (Ramanathan and Carmichael, 2008) and can exert significant impacts on global and regional climate, planetary boundary layer height (PBLH), air quality and human health, etc. (Lee et al, 2017; Bond et al, 2013; Ding et al, 2016)
The mass ratios of different factors to BC have a smaller influence from PBLH; high levels of fossil fuel combustion OA (FFOA) / BC strongly indicate that co-emitted organic species with BC from fossil fuel combustion were enhanced at nighttime
We found the average concentrations of BC and its coating species were 4.9 and 24.5 μg m−3; the ratio of coating to BC core (RBC) was ∼ 5.0
Summary
Black carbon (BC) is generated from incomplete combustion of carbon-based fuels (Ramanathan and Carmichael, 2008) and can exert significant impacts on global and regional climate, planetary boundary layer height (PBLH), air quality and human health, etc. (Lee et al, 2017; Bond et al, 2013; Ding et al, 2016). To the best of our knowledge, no study was conducted in real time to characterize the chemical compositions exclusively of BC-containing particles in Beijing despite the aforementioned important effects of coating materials on BC properties. Laser-only SP-AMS can exclusively measure BC cores and the species coated on BC cores This unique technique allows us to explore the characteristics of BC-coating species in detail with no perturbations from other co-existing non-BC containing particles in ambient air. As part of the UK–China Atmospheric Pollution & Human Health (APHH) study (Shi et al, 2018), we report for the first time the real-time measurement results on the chemical composition, mass loading, size distribution and sources/processes of BC-containing particles during the wintertime of 2016 in urban Beijing. Results regarding physical properties and optical properties are presented in Liu et al (2018) and Xie et al (2019) of this special issue, respectively
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