Qiao et al. (2025) Particle Size as a Key Driver of Black Carbon Wet Removal: Advances and Insights

Identification

• Journal: Atmosphere
• Year: 2025
• Date: 2025-11-20
• Authors: Yumeng Qiao, Jiajia Wang, Li Wang, Baiqing Xu
• DOI: 10.3390/atmos16111309

Research Groups

• State Key Laboratory of Tibetan Plateau Earth System, Resources and Environment, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
• University of Chinese Academy of Sciences, Beijing 101408, China

Short Summary

This paper reviews recent research on the size dependence of black carbon (BC) wet removal, highlighting that particle size is a critical driver influencing its atmospheric lifetime and climate impact, with significant uncertainties remaining in observational coverage and model parameterization.

Objective

• To systematically summarize the mechanisms governing the size dependence of black carbon (BC) wet removal.
• To evaluate current observational and modeling results concerning BC wet removal efficiency.
• To identify existing research gaps and outline future research directions to more accurately constrain BC's role in the climate system.

Study Configuration

• Spatial Scale: Global, regional (e.g., East Asia, South Asia, Europe, North America, Arctic, Tibetan Plateau), urban, remote, and high-altitude environments.
• Temporal Scale: Short-term (hours to days for aging), long-term (seasonal variations, historical trends over 50 years).

Methodology and Data

• Models used: GEOS-Chem, ECHAM-HAM, GISS ModelE, WRF-Chem, TOMAS (TwO-Moment Aerosol Sectional), GLOMAP-bin, SALSA2.0, M7 modal scheme, particle-resolved models.
• Data sources: Field observations (ground-based, aircraft campaigns), laboratory and cloud chamber experiments, SP2 (Single-Particle Soot Photometer) coupled with CCN counters (CCNc), HTDMA (Humidified Tandem Differential Mobility Analyzer), APM/CPMA (Aerosol or Centrifugal Particle Mass Analyzers), precipitation samples, ice core records.

Main Results

• Particle size is a critical factor determining black carbon (BC) wet removal efficiency, linking atmospheric aging processes to its ultimate removal.
• Freshly emitted BC particles, typically small (tens to several hundred nanometers) and hydrophobic, require higher critical supersaturation (Sc) for activation as cloud condensation nuclei (CCN).
• Atmospheric aging, involving interactions with sulfates, nitrates, or organic matter, increases BC particle size (e.g., geometric mean diameter growing from ~80 nm to over 200 nm) and hydrophilicity, which lowers Sc and enhances CCN activation and wet removal.
• Wet deposition is the primary removal pathway for BC (approximately 60-85% of total deposition), with in-cloud scavenging preferentially removing larger, aged BC in the accumulation mode (100-300 nm), while below-cloud scavenging can remove smaller particles.
• Observational studies consistently demonstrate the strong influence of particle size, coating thickness, and mixing state on BC activation potential and wet removal efficiency.
• Modeling studies indicate that uncertainties in BC particle size distribution and aging rates lead to significant discrepancies (e.g., 20% to 40% variation in atmospheric lifetime, up to 30% variation in climate impact estimates) in simulated transport, deposition, and radiative forcing.
• Regional differences in emission sources, atmospheric composition, and meteorological conditions (e.g., monsoon systems, temperature inversions) result in distinct BC aging pathways, size distributions, atmospheric lifetimes, and climatic impacts.

Contributions

• Provides a comprehensive, systematic review of the size dependence of black carbon (BC) wet removal, integrating theoretical mechanisms, observational evidence, and modeling advancements.
• Highlights the critical role of particle size as a key driver linking BC aging processes to its atmospheric lifetime and climate impacts.
• Identifies significant research gaps, particularly in the systematic quantification of size-dependent wet removal mechanisms in multi-cloud systems and the refinement of model parameterizations.
• Proposes a clear roadmap for future research, emphasizing the need for enhanced long-term observations, advanced measurement technologies, improved size-resolving model capabilities, and interdisciplinary research frameworks.
• Offers a robust scientific basis for understanding BC's atmospheric behavior, assessing its climatic effects, and informing regional air quality management and global climate policies.

Funding

• Excellent Research Group for Tibetan Plateau Earth System (grant number No. 42588201)
• Basic Science Center for Tibetan Plateau Earth System (grant number 41988101)
• Second Tibetan Plateau Scientific Expedition and Research Program (grant number 2019QZKK0101)

Citation

@article{Qiao2025Particle,
  author = {Qiao, Yumeng and Wang, Jiajia and Wang, Li and Xu, Baiqing},
  title = {Particle Size as a Key Driver of Black Carbon Wet Removal: Advances and Insights},
  journal = {Atmosphere},
  year = {2025},
  doi = {10.3390/atmos16111309},
  url = {https://doi.org/10.3390/atmos16111309}
}