Xu et al. (2025) Evaluating and Improving Light Absorption Retrievals of Black Carbon Using In Situ Polar Nephelometry

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Repository for Publications and Research Data (ETH Zurich)
• Year: 2025
• Date: 2025-10-07
• Authors: Xu, Qizhi, Bertozzi, Barbara, Modini, Robin Lewis, Brem, Benjamin Tobias, Müller, Thomas, Romshoo, Baseerat, Mohr, Claudia, Gysel-Beer, Martin
• DOI: 10.3929/ethz-c-000786338

Research Groups

Not explicitly stated in the provided text.

Short Summary

This study addresses the inaccuracy of black carbon (BC) remote sensing retrievals due to the common assumption of spherical morphology. It demonstrates that using the Multi-Sphere T-Matrix (MSTM) method, which accounts for BC's fractal-like morphology, significantly improves the accuracy of retrieved BC properties like absorption coefficient and volume concentration, compared to standard Lorenz-Mie theory.

Objective

• To improve the accuracy of remote sensing retrievals for black carbon (BC) light absorption by evaluating the impact of particle morphology assumptions.
• To compare the performance of the Multi-Sphere T-Matrix (MSTM) method, which accounts for fractal-like morphology, against standard Lorenz-Mie theory using laboratory polarimetric measurements of BC aggregates.

Study Configuration

• Spatial Scale: Laboratory-scale, focusing on individual black carbon aggregates (nanometre to micrometre range).
• Temporal Scale: Controlled laboratory experiments (short-term, specific measurement durations).

Methodology and Data

• Models used: Lorenz-Mie theory, Multi-Sphere T-Matrix (MSTM) method.
• Data sources: In situ polarimetric measurements of bare black carbon aggregates generated in a laboratory setting, using a newly developed polar nephelometer (uNeph).

Main Results

• Standard retrievals based on Lorenz-Mie theory poorly reproduced the phase function and polarized phase function of black carbon (BC), leading to significant bias in retrieved properties.
• The Multi-Sphere T-Matrix (MSTM) method achieved good closure between measured and simulated phase functions for BC aggregates in the accumulation size range.
• Black carbon properties, specifically absorption coefficient and volume concentration, were accurately and precisely retrieved by accounting for the fractal-like morphology using MSTM.
• Only two additional parameters were required for the MSTM retrieval, suggesting its practical feasibility for atmospheric remote sensing.

Contributions

• Demonstrates the critical importance of accounting for the fractal-like morphology of black carbon (BC) aggregates to accurately retrieve their optical properties, challenging the common spherical assumption.
• Validates the Multi-Sphere T-Matrix (MSTM) method as a superior approach for retrieving BC properties compared to Lorenz-Mie theory, achieving good closure with experimental data.
• Suggests the practical feasibility of incorporating aggregate morphology into real atmospheric remote sensing retrievals of BC, requiring minimal additional parameters.
• Contradicts previous studies by demonstrating good closure between measured and simulated phase functions for BC aggregates using MSTM.

Funding

Not explicitly stated in the provided text.

Citation

@article{Xu2025Evaluating,
  author = {Xu, Qizhi and Bertozzi, Barbara and Modini, Robin Lewis and Brem, Benjamin Tobias and Müller, Thomas and Romshoo, Baseerat and Mohr, Claudia and Gysel-Beer, Martin},
  title = {Evaluating and Improving Light Absorption Retrievals of Black Carbon Using In Situ Polar Nephelometry},
  journal = {Repository for Publications and Research Data (ETH Zurich)},
  year = {2025},
  doi = {10.3929/ethz-c-000786338},
  url = {https://doi.org/10.3929/ethz-c-000786338}
}