How Black Carbon Aerosols Evolve During Combustion

Scientists in China, in collaboration with researchers in Japan, have analyzed how black carbon aerosols change in number and size during combustion.

AsianScientist (Dec. 29, 2017) – A team of researchers in China and Japan has measured the number and sizes of black carbon aerosols under various combustion conditions. Their findings have implications for climate change and have been published in the journal Atmospheric Chemistry and Physics.

Black carbon aerosols in the atmosphere play a vital role in climate change by absorbing solar radiation and altering the formation, lifespan and reflective properties of clouds. They also provide the ‘seed’ for haze formation in urban areas.

In northern China, open biomass burning (OBB), such as straw burning after harvesting, is an important source of refractory black carbon (rBC). OBB emits both soot particles and a substantial amount of semi-volatile organic matters, both of which will undergo a very complicated mixing and evolution processes in the atmosphere, affecting their ability to form cloud condensation nuclei.

At present, the mixing state of OBB aerosols is usually assessed through field studies. Due to influences such as meteorological factors, diffusion and transmission, the mixing state of rBC changes significantly with time. To better characterize the aging process of rBC, studies on freshly emitted rBC during the whole combustion process are urgently needed.

In this study, Dr. Pan Xiaole from the Chinese Academy of Sciences’ Institute of Atmospheric Physics and his Japanese collaborators conducted combustion lab experiments to simulate and investigate rBC emission and mixing state characteristics under different combustion conditions. The researchers found that the diameter of rBC particles decreased as the combustion state of biomass shifted from flaming-dominant to smoldering-dominant.

“This result indicates that the rBC coagulation and growth process was intensive during flaming combustion, caused by substantial production of rBC precursor particles,” said Pan.

However, the researchers found that the coating of rBC particles by semi-volatile organic matter was 20 percent thicker during smouldering combustion. This was due to the strong emission of semi-volatile organic matter, coupled with the lower production rate of rBC particles during smoldering combustion. Collectively, these findings provide a comprehensive understanding of how rBCs evolve during combustion of biomass.

The article can be found at: Pan et al. (2017) Emission Characteristics of Refractory Black Carbon Aerosols from Fresh Biomass Burning: A Perspective from Laboratory Experiments.


Source: Chinese Academy of Sciences; Photo: Shutterstock.
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