the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Sep 2025
Evolution of water-soluble organic carbon in neglected coal dust particles influenced by ozone aging
Abstract. Coal mining and utilization generate substantial amounts of coal dust, of which the portion in fine particles can travel long distances and further impact climate and air quality through atmospheric aging processes. However, the evolutionary behavior of water-soluble organic carbon (WSOC) in fine coal dust remains unclear. In this study, the aging of coal dust particles and their WSOC processed by ozone (O3) under dark conditions was investigated in a flow tube reactor. Results show that O3 aging significantly enhanced the hydrophilicity, light absorption, and fluorescence intensity of WSOC. During the aging process, both carbon loss and gain were observed in WSOC, with the amount of carbon gain exceeding lost through the generation of volatile species. Although the mass absorption efficiency (MAE365) of fresh WSOC was initially low, the O3 aging process significantly increased the MAE365 of WSOC by a factor of 8.8 to 18.2 through the formation of strongly absorbing hydrophilic conjugated compounds. The radiative forcing of WSOC may be underestimated if WSOC absorption linked to atmospheric aging is not accounted for in models. These findings suggest that the long-term O3 aging effect on coal dust may become prevalent in the background of the complex atmospheric particulate matter and O3 pollution in China, policymakers should reconsider air quality improvement strategies.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-3084', Anonymous Referee #1, 15 Sep 2025
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RC2: 'Comment on egusphere-2025-3084', Anonymous Referee #2, 26 Sep 2025
This manuscript deals with the chemical characterization of coal dust exposed to ozone. The exposure experiments were carried out in a flow tube reactor and the chemical modifications of the samples were traced by means of a suite of spectroscopic techniques. The changes in the UV-VIS absorbivity were probed aiming to assess the evolution in the aerosol optical properties. Finally, the release of volatile reactive carbonyls, which are important secondary pollutant precursors, was also characterized. Since coal dust emissions are widespread in many countries and poorly characterized, the science topic is sound and of potential interest for ACP readers. However, this is mainly a study of analytical chemistry and spectroscopy, while the atmospheric implications remain undetermined, because the results are just not reported in appropriate units. For instance, the “emissions of carbonyl compounds” in Table 2 are reported in micrograms per cubic meter, but this is not an emission rate per dust mass unit, it is just a concentration measured in the outflow of the flow tube reactor, so it is impossible to understand whether such emissions are large or small. Similarly, the WSOC concentrations in Figure 4 are just concentrations measured in an aqueous extract, not the “WSOC content of particles” stated in the legend. Finally, translating a measure of mass absorption efficiency (MAE) into a forcing efficiency (SFE) (Fig. 9 and Conclusions) remains ambiguous in the context of an experiment which is merely based on material characterization without any real measurements in the ambient air. It is also not clear what is the physical meaning of the cumulative SFE increase from the MMC-D and HMC-D samples: why the two series of values, from two independent samples, are reported in a staked bar chart (Fig. 9)? Sometimes, the discussion is highly speculative or unsupported by clear experimental evidence (for instance, lines 223 – 229 about the link between the XPS functional groups and WSOC release). Section 3.3.3 about fluorescence characteristics employs concepts, such as “protein-like”, “humification” and “biodegradation”, that would deserve some clarifications when applied to a fossil form of carbon or to an aerosol. Finally, the presentation of the results is difficult to follow, because Section 2 lacks a clear schematic for the ageing experiment (where is the sample in Fig. 1? And the carbonyl sampling apparatus?) as well as for the analytical protocol. In summary, in this reviewer’s opinion, the manuscript in its present form does not meet the quality standards of ACP.
Citation: https://doi.org/10.5194/egusphere-2025-3084-RC2
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Evolution of water-soluble organic carbon in neglected coal dust particles influenced by ozone aging Yuanyuan Qin, Lin Yi, Peng Yi, Juanjuan Qin, Xueming Zhou, Chenglong Zhang, Zhao Shu, Yuwei Gao, Jihua Tan, and Lin Zhao https://doi.org/10.5281/zenodo.15767166
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This manuscript investigated the evolution of water-soluble organic from coal dust on flow tube experiment by ozone aging. The chemical compositions/structural of coal dust were analyzed by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The traces gas was measured by high-performance liquid chromatography. In addition, they also use tree-dimensional fluorescence spectroscopy and ultraviolet-visible absorbance spectroscopy to measure the fluorescence and absorption. This manuscript structure is only followed by data from different instruments. It looks like data report. It was lack novel and innovation. In addition, the figures and discussion in the manuscript are very rough. Furthermore, this work only provide fluctional group and properties of water soluble organic matter. It has not more molecular information. Therefore, this manuscript quality is not suitable to publish into atmosphere chemistry and physics. I suggest this manuscript should be rejected. Here are my main comments.