the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Jan 2025
Characterizing lead-rich particles in Beijing's atmosphere following coal-to-gas conversion: Insights from single particle aerosol mass spectrometry
Abstract. Coal-to-gas (CTG) policies are important energy transformation strategies to address air pollution issues, but how well it improves atmospheric Lead (Pb) pollution remains poorly understood. By the end of 2018, Beijing had achieved coal-free in urban and plain areas. The mixing state and atmospheric chemical processes of Pb-rich particles in Beijing were monitored using a single particle aerosol mass spectrometry (SPAMS) during 2019. Based on a large dataset of mass spectra, this study find that the number fractions of Pb-rich particles, as well as two types of Pb-rich particles (K-Na-EC and K-OC) related to coal combustion during heating period, show lower than those after the heating period. Based on concentration-weighted trajectory plots, the results indicate that lead aerosols mainly derive from the transmission of surrounding provinces. Lead nitrate is one of the important forms of lead in aerosol particles, most contributed by photo-chemical reactions in spring, fall, and winter. Due to the decomposition of nitrate during high temperatures, the aqueous reactions mechanism contributes more to lead nitrate in summer. These results improve our understanding of the seasonal distribution, formation mechanisms, and influencing factors of toxic Pb-containing particles after CTG.
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RC1: 'Comment on egusphere-2024-3469', Anonymous Referee #1, 04 Feb 2025
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This study measures the mixing state and atmospheric chemical processes of Pb-rich particles in Beijing were monitored using a single particle aerosol mass spectrometry (SPAMS) during 2019. The results showed the number fractions of Pb-rich particles, as well as two types of Pb-rich particles (K-Na-EC and K-OC) related to coal combustion during heating period, show lower than those after the heating period. Based on concentration-weighted trajectory plots, the results indicate that lead aerosols mainly derive from the transmission of surrounding provinces. Due to the decomposition of nitrate during high temperatures, the aqueous reactions mechanism contributes more to the formation of lead nitrate in summer. This study can improve our understanding of the seasonal distribution, formation mechanisms, and influencing factors of toxic Pb-containing particles after CTG. However, some critical information is missing, several issues need to be revised. I recommend the manuscript be revised before being accepted for publication.
1. Introduction section. Lines 63-72, the authors summarize the literature related to the application of SPMAS to the mixing state, sources, and atmospheric evolutionary processes of Pb. What are the key information in these studies, and please provide a brief description, which will benefit the reader in recognizing the practical applications of SMPAS to relevant scientific problems.
2. Whether a dehumidifier is added to the air inlet of the aerosol instrument during the collection period.
3. There is an interesting phenomenon in Fig. S1, the correlation between Pb-containing particles and Pb-rich particles in winter is much lower than the correlation in other seasons, what may be the reason for this, it will be clearer if the authors can give further explanation.
4. Line 140, "the number fraction of Pb-EC particles was significantly higher during the winter heating period in 2014 than before the heating period (Peng et al., 2020)". How much higher, please give a quantitative number so the comparison will be more visual.
5. Line 200, "which may be related to the longer sampling time during the HP in winter (6 days) compared to spring (31 days) ". How sampling time affects the higher total relative number fractions of K-Na-EC and KOC particulate matter in winter, please describe.
6. Line 223, "In this study, almost all lead are internally mixed with nitrate， which is much higher than its mixing with sulfate, chlorine, and oxygen." Mixing states are categorized as internal and external mixing, and how the authors determined that almost all of the lead in the manuscript was internally mixed with nitrate, rather than externally mixed.
7. Lines 241-242, "Furthermore, the number fractions of Pb-N particles increased with increasing t, but does not increase with increasing RH and NO2, and even decreases with increasing relative humidity.". The number fractions of Pb-N particles do not increase with the increase of relative humidity and NO2, and even decrease with the increase of relative humidity, what is the reason for this phenomenon?
8. Conclusions. Line 266, "which is higher in summer and fall than in spring and winter".
It is recommended to give comparisons on the data, which should be noted in other similar places in the text, to make the manuscript more rigorous.
9. Conclusions. "Photochemical oxidation is the main pathway for the formation of particulate lead nitrate in spring, fall, and winter, with high values occurring from 10: 00−15: 00. Aqueous reaction is the main pathway for the formation of lead nitrate in summer, with high values occurring from 00:00−10:00.". How did the authors determine which of the photochemical oxidation and aqueous reaction was the dominant pathway in the different seasons, and the timeframe, which doesn't seem to be meticulously described in section 3.4 of the manuscript?Citation: https://doi.org/10.5194/egusphere-2024-3469-RC1 -
RC2: 'Comment on egusphere-2024-3469', Anonymous Referee #2, 28 Feb 2025
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This manuscript presents a field observational study on the measurement of lead-rich particles using a single-particle aerosol mass spectrometer (SPAMS) in Beijing. The study draws interesting conclusions that contribute to deepening our understanding of the seasonal distribution, formation mechanisms, and influencing factors of toxic lead particles following the coal-to-gas conversion. Although the study is localized to Beijing, the findings have broader implications, especially in terms of human intervention and policy making related to lead pollution. The reduction of lead in the atmosphere due to the coal-to-gas conversion can serve as an important case study for other regions facing similar air quality challenges. I recommend publication of the manuscript after the authors address the following comments:
- The manuscript should include a clearer explanation of how the internal and external mixing states of lead particles were determined. It would be helpful to expand on the methodology used to identify and categorize these mixing states for better transparency.
- Some sections of the manuscript contain complex phrasing that could benefit from greater clarity. For example, certain sentences related to the comparison of Pb-rich particle types between heating and non-heating periods are dense and need to be simplified for better readability. Additionally, the explanation of the factors influencing Pb nitrate formation could be more explicit.
- Lines 120-123: “They are named potassium-sodium (K-Na), K-Na internally mixed with Fe (K-Na-Fe), K-Na internally mixed with Cu (K-Na-Cu), K-Na internally mixed with Zn (K-Na-Zn), K-Na internally mixed with elemental carbon (K-Na-EC), and potassium internally mixed with organic carbon (K-OC).”
- Lines 124-131: Although the method for selecting lead nitrate used in this manuscript has been employed in previous research, I wonder if this selection method could potentially underestimate the content of lead nitrate. Could this affect the conclusions of the study?
- Several sentences in the manuscript require revision for clarity. The authors should pay close attention to sentence structure and tense consistency, as seen in the comments on lines 25, 54, and 280-281. Ensuring clear and precise language will improve the overall readability of the paper.
Lines 229-230: This sentence is unclear. Please rewrite it for better clarity.
Lines 232-233: This sentence should be described more specifically so that readers can clearly understand how the mixture of lead and nitrate differs from other components.
Line 25: “but how well it improves...” — Correct the tense.
Line 54: “Pb(NO3)2 generates from the chemical transformation of PbO and PbCl2 in the atmospheric process.” — Correct the grammar.
Line 218: “to doubled” — Correct the grammar.
Lines 280-281: “The study included heating and non-heating periods, and the results emphasized the importance of heterogeneous hydrolysis during the heating period before 'coal-to-gas' on the formation of Pb(NO3)2.”— Please check and correct.
Citation: https://doi.org/10.5194/egusphere-2024-3469-RC2
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