Recently, Prof. Dantong Liu from the School of Earth Sciences, Zhejiang University, published a paper in Nature Geoscience, titled “Warming potential of atmospheric BC modulated by particulate matter.” The study was conductedby Professor Liu in collaboration with multiple universities and research institutions worldwide.

Black carbon aerosol (BC) consists of light-absorbing particulate matter produced by incomplete combustion, and is a key short-lived climate forcing agent contributing to global warming. After entering the atmosphere, BC does not exist in a single fixed form. It mixes with non-black-carbon components, forming a coating around the BC core. These coatings can change light-absorption capacity of BC, cloud condensation nuclei activity, and atmospheric lifetime, thereby affecting its direct and indirect radiative effects. A global characterization of BC mixing state has long been a challenge in model simulations. How to efficiently characterize BC coatings using routinely available observational quantities is an urgent scientific problem for accurately assessing BC’s warming effect. By integrating a large volume of global ground-based and aircraft observations, this study proposed a new method for quantifying BC coatings using routinely observed particulate matter, PM_2.5, and BC mass concentration. This enables efficient quantification of BC’s direct and indirect radiative effects at the global scale.

Figure 1. Global observations of the BC mixing state.

The study integrated observations of BC coatings from ground stations and aircraft platforms across many regions worldwide, covering urban areas, suburban areas, remote regions, and areas affected by biomass burning.

PM_2.5 Provides Observable Clues for BC Coatings

The research team found a stable positive correlation between the volume ratio, VR, of BC coatings to refractory BC and the PM_2.5/BC ratio. Because BC mainly comes from primary emissions, while a considerable portion of PM_2.5 is formed secondarily, PM_2.5/BC can to some extent reflect the non-black-carbon material that can condense onto the surface of BC. This pattern is broadly applicable across ground and aircraft observations in different environments, laboratory smog-chamber simulations, and particle-resolved models.

Figure 2. Relationship between BC coatings and PM2.5 and BC mass concentration.

Global observations, laboratory simulations, and particle-resolved models all support the positive correlation between VR and PM/BC.

Based on this relationship, the study proposed the PM-BC method: first estimating the slope between PM/BC and VR from BC concentration, and then deriving VR from PM/BC. The method establishes empirical parameters separately for urban sources and biomass-burning sources, preserving differences among source types while greatly reducing the computational cost of global-scale application.

Coatings Make BC More Light Absorbing and More Likely to Enter Clouds

Applying the PM-BC method to global data showed that BC coatings significantly enhance BC’s light-absorption capacity. In 2019, accounting for coatings increased the global mean direct radiative effect of BC from 0.20 +/- 0.25 W m-2 to 0.30 +/- 0.42 W m-2.

Figure 3. Radiative effects of BC caused by coatings.

The study further assessed near-surface VR, changes in top-of-atmosphere radiative flux caused by coatings, and spatial changes in VR under future scenarios.

The influence of coatings is not limited to direct radiative effects. As VR increases, the size and hygroscopicity of BC particles also increase, enabling more BC to enter low-level cloud liquid water as cloud condensation nuclei. BC in liquid water constrained by VR produces an additional global radiative effect of about 0.065 +/- 0.15 W m^-2, with a more prominent influence from BC emitted by biomass burning.

The Future Urban BC Effects May Decline While Biomass Burning Becomes a Greater Challenge

The study further applied the PM-BC method to future scenario projections for 2019-2080. The results show that under most CMIP6 scenarios, near-surface PM_2.5 and BC concentrations in urban areas tend to decline. As a result, the coating volume ratio and warming influence of urban BC are expected to weaken. By contrast, PM_2.5 in biomass-burning regions declines more slowly and may even increase under some scenarios, making BC coatings and their radiative influence more persistent in these regions.

Figure 4. Conceptual framework for particulate matter modulation of BC mixing state and radiative effects.

PM_2.5 can influence BC’s absorption enhancement and ability to participate in cloud processes by modulating BC coatings.

This finding suggests that while urban air-quality improvement continues to advance, future control of BC emissions from wildfires and biomass burning will become an important part of mitigating the climate-warming effects of BC. Because the global warming may cause increased wildfire risk, the climate effects of biomass-burning BC need greater attention in observations, modeling, and policy assessment.

Author information

Dantong Liu is a Hundred-Talents Program Professor in the School of Earth Sciences, Zhejiang University. His research focuses on atmospheric chemistry, atmospheric aerosols, and cloud microphysics. He has conducted original research on the optical properties of carbonaceous aerosols, cloud particle activation, and their evolution and removal processes in the atmosphere. He has published more than 190 SCI papers in leading international journals, including more than 90 first-author or corresponding-author papers in journals such as Nature Geoscience. His work has been cited more than 11,000 times, with an h-index of 54. His research achievements have been highlighted by AGU and EGU. He has led multiple projects funded by the National Natural Science Foundation of China and the National Key Research and Development Program. He also serves on the editorial boards of journals including Atmospheric Chemistry and Physics and Aerosol Science and Engineering. He also serves as a council member of the Chinese Society of Particuology, a member of the Weather Modification Professional Technical Committee of the Chinese Meteorological Society, and a member of the academic committee of the China Meteorological Administration Key Open Laboratory for Cloud Precipitation Physics and Weather Modification. He has received academic honors including the Young Particuology Award of the Chinese Society of Particuology, the Young Scientist Award of the Chinese Society for Environmental Sciences, the Xie Yibing Young Meteorological Science and Technology Award, and the Science and Technology Award of the China Meteorological Service Association.

Article details: https://www.nature.com/articles/s41561-026-02068-0

Reference source: Atmospheric Chemistry WeChat official account