Method to Quantify the Black Carbon Aerosol Light Absorption Enhancement with Entropy and Diversity Measures

Abstract

Abstract. Large uncertainties remain when estimating the warming effects of ambient black carbon (BC) aerosols on climate. One of the key challenges in modeling the radiative effects is predicting the BC light absorption enhancement, which is mainly determined by its mass ratio of non-BC coating thickness to BC (MR). For the same MR, recent researches find that the radiative absorption enhancements by BC are also controlled by its particle-to-particle heterogeneity. In this study, the BC mixing state index (χ) is developed to quantify the dispersion of ambient black carbon aerosol mixing states based on binary systems of BC and other non-black carbon components. We demonstrate that the BC light absorption enhancement increases with χ for the same MR, which indicates that χ can be employed as a factor to constrain the light absorption enhancement of ambient BC. Our framework can be further used in the model to study the black carbon radiative effects on climate change.

Quantifying the structural uncertainty of the aerosol mixing state representation in a modal model

“…As a comparison, χ MAM4 o ranged from 92 % to 97 % in winter and from 87 % to 95 % in summer. A caveat when comparing χ ML o and χ MAM4 o , respectively, with the observations reported in Zhao et al (2021) and Yu et al (2020) is that the definition of χ ML o and χ MAM4 o included BC-free particles, while the χ values in the measurements byZhao et al (2021) andYu et al (2020) were calculated only considering the subpopulation of BC-containing particles. This might introduce a bias in the mixing state index between the χ o index used in this paper and the observations (depending on the fraction of the BC-free particles present at any given location).…”

“…We further compared the ML model estimates using recent observations from China. Specifically, we compared χ ML o and χ MAM4 o with χ values from Taizhou (Zhao et al, 2021) and Beijing (Yu et al, 2020) We can also relate our χ o index qualitatively to the SP2 measurements in the Finnish Arctic during winter 2011-2012 (Raatikainen et al, 2015). Although this study did not provide quantitative mixing state index calculations, it is an important finding that BC-containing particles (with various amounts of coatings) co-existed with BC-free particles.…”

Quantifying the structural uncertainty of the aerosol mixing state representation in a modal model

“…We further compared the ML model estimates using recent observations from China. Specifically, we compared χ ML o and χ MAM4 o with χ values from Taizhou (Zhao et al, 2021) and Beijing (Yu et al, 2020) We can also relate our χ o index qualitatively to the Single Particle Soot Photometer measurements in the Finnish Arctic during winter 2011-2012 (Raatikainen et al, 2015). Although this study did not provide quantitative mixing state index calculations, it is an important finding that BC-containing particles (with various amounts of coatings) co-existed with BC-free particles.…”