A Chinese study team at Anhui Institute of Optics and Fine Mechanics (AIOFM), Hefei institutes of Physical Science found that the photochemistry played a role in absorption enhancement of BC-containing particles.

This work was done by ZHANG Weijun and his team and their work was published in Atmospheric Chemistry and Physics.

Black carbon (BC) is the most efficient light-absorbing component of atmospheric aerosols and plays an important role in the global climate system. They are produced by incomplete burning of fossil fuels, biofuel, and residual biomass. Atmospheric BC particles undergo several aging processes that would dramatically change the morphology and mixing state of BC-containing particles, thereby altering their optical properties.

The light absorption enhancement of BC particles caused by coating is quantified by E_abs, the ratio of the absorption coefficients of coated and bare BC. However, the mechanisms of enhancing BC absorption remain elusive due to the complexity of the aging process and its varied sources.

To aim that question, the team took a close look at the absorption enhancement of BC-containing particles and found the key role of modifying the absorption enhancement of BC-containing particles.

In their work, the influence of photochemical aging on E_abs and aerosol single scattering albedo (w, defined as the ratio of scattering to extinction coefficients) at Shouxian National Climatology Observatory in east China during the summer was studied by using a thermal denuder approach combined with a self-developed cavity-enhanced albedometer. The concentration of O_x (O_x = O₃ + NO₂) was used as a proxy for atmospheric photochemical aging.

They found that the absorption amplification depended on the coating thickness and the absorption of coating materials, and photochemistry played a role in modifying the absorption of BC-containing particles.

This research is supported by the National Natural Science Foundation of China, the Natural Science Foundation of Anhui Province, the Youth Innovation Promotion Association CAS, and the China Special Fund for Meteorological Research in the Public Interest.

Scatter plot of E_abs and w for different photochemical oxidant concentrations. Variation in the observed diurnally averaged absorption enhancement and SSA (solid points, colour-coded with respect to the concentrations of O_x) is used for the modelling constraint. Both E_abs and w increase with O_x mixing ratio. (Image by XU Xuezhe)