the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Aug 2024
Significant role of biomass burning in heavy haze formation in a megacity: Molecular-level insights from intensive PM2.5 sampling on winter hazy days
Abstract. Reports on molecular-level characterization of primary and secondary constituents in PM2.5 at high-time resolution are limited to date, especially during haze events. The study explored molecular composition and source contributions of PM2.5 with comprehensive analytical methods by conducting intensive sampling at roughly 2-hour intervals during hazy days in winter. Results show that organic matters were the predominant species, followed by NO3-. Biomass burning (BB) was the biggest contributor to organic carbon (OC), both in concentration and in proportion. Radiocarbon analysis of carbonaceous fractions reflects that fossil fuels dominate water-soluble organic carbon (WSOC) (61–82 %) likely resulting from increased coal combustion for residential cooking and heating and the coal-fired industry in cold times. Interestingly, the contribution of non-fossils instead of fossil fuels to WSOC enhanced with aggravating haze pollution, coinciding with significantly intensified BB during that time. Other non-fossil sources, including fungal spores and plant debris, showed a larger contribution to OC in light haze episodes. For secondary sources, naphthalene-derived secondary organic carbon (SOC) contributed more to OC in PM2.5 (0.27–2.46 %) compared to biogenic emissions (0.05–1.10 %), suggesting fossil fuels may dominate SOC formation during urban haze events. SOC declined with rising haze pollution and presented high levels on days with high temperature and low relative humidity due to elevated photooxidation. Additionally, BB can raise secondary formation as well as the emissions of other sources, as demonstrated by the significant relationships between BB tracers and many other source tracers. These findings illustrate that BB likely plays a significant role in the heavy winter haze.
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Status: open (until 30 Sep 2024)
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RC1: 'Comment on egusphere-2024-2098', Anonymous Referee #1, 27 Aug 2024
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This study provides many valuable information on the molecular-level PM2.5 components during different levels of haze events with high-time resolution. It analyzed a wide range ofindividual components of PM2.5, which allows a detailed study of various sources at the same time. The radio carbon measurements suggest a greater contribution from fossil fuels to WSOC, while the contribution of non-fossil fuels increased with increasing haze pollution, coinciding with elevated biomass burning (BB) during that time. This new finding highlight BB may be an important driver for heavy haze formation, despite great contributions of fossil fuel sources. This manuscript presents many interesting results that will deepen our understanding of haze evolution. This work is worth being published in the journal of ACP.
Here are some minor comments below:
In Figure 4, I noticed that sugars and sugar alcohols have high concentrations during the last two periods, with levels relatively higher than those of anhydrosugars. Could you explain why this is the case?
This study conducted 14C analysis on WSOC. Why did the authors choose WSOC over other PM2.5 components?
The sampling period is from December 31 to January 2. Why was this specific period selected? Does it overlap with the Spring Festival or any holidays?Citation: https://doi.org/10.5194/egusphere-2024-2098-RC1 -
RC2: 'Comment on egusphere-2024-2098', Anonymous Referee #2, 29 Aug 2024
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This publication aims to determine the levels of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 both indoors and outdoors during the APEC summit. The objective is to obtain data that can be used to develop policy related to the evaluation of indoor PAH exposure. This investigation is crucial for evaluating the air quality during the duration of the research. Furthermore, there are some challenges that require significant editing and must be addressed before accepting this manuscript in the Air Quality, Atmosphere, and Health Journal. Please look at the additional comments for more information.
- Line 38, 53, page 1: Please adjust the significant number.
- Line 36 – 42, page 1: The sentence looks confused; please revise.
- Line 53 – 55, page 1: Please pay attention to conclusion’s expression.
- Please rechecked the space in the sentence such as in line 7, page 2; ….attention(Mesquita et al. 2014)
- Line 24, page 2: Avoid repeating the full name.
- Line 4, page 3: Please add more references.
- Line 21,24, page 4: Please change PAH to PAHs and revise everywhere in the manuscript.
- Line 42 – 43, page 4: Please indicate the significance of the period for sampling (during and after source control).
- Line 52 – 54, page 4: Before the samples, the authors baked the quartz filter at 450°C for 5 hours. Is there a standard procedure for this temperature and baking duration?
- Following from the previous question, do you have any standard for controlling the weight of the filter?
- Line 1 – 3, page 5: Please explain the procedures for this step in PAH extraction.
- Line 19, page 5: Please rewrite PM2.5 to PM5.
- Line 52 – 53, page 6: Avoid repeating the full name, and please review the other point in the manuscript.
- The results recommend enriching and describing the levels of PM5 indoors and outdoors, as well as comparing them to other studies.
- All figures are not clear, please redraw and change the alphabet as the same in the texts.
- Line 21,29, page 9: Please use abbreviation.
- Line 36 – 37, page 9: Please explain the reason for this phenomenon in this section.
- Line 21,29, page 9: Please explain the reason for this phenomenon in this section.
- Line 33 – 39, page 10: Can you explain this phenomenon?
- Line 29 – 32, page 11: It is advisable to include references.
- I recommend that the conclusions be evaluated and revised instead of duplicating the content from the results and statements section.
Citation: https://doi.org/10.5194/egusphere-2024-2098-RC2 -
RC3: 'Comment on egusphere-2024-2098', Anonymous Referee #3, 29 Aug 2024
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This study explored the molecular levels of inorganic and organic components in wintertime PM2.5 using intensive sampling and a range of techniques. It also assessed the contributions of primary and secondary sources with tracer-based methods. The finding that BB may significantly influence haze formation is notable, especially compared to the fossil-dominated conditions typically observed in winter. In this regard, the biomass-burning contribution to haze can more clearly be identified compared to some recent studies conducted in India, where BB is consistently prominent, particularly during haze events. Overall, the whole manuscript is well organized. I recommend the manuscript for publication on ACP after the following comments have been well addressed.
Major comments:
In lines 75-77: The authors categorized biomass burning as an anthropogenic source. While biomass burning refers to the combustion of organic materials like wood, crop residues, and other plant matter, which releases VOCs into the atmosphere. In this context, these VOCs are biogenic. Could you explain this?
In lines 136-145: Was the extraction procedure and measurement process for sugar compounds the same as for ions when using ion chromatography?
In lines 161-162: Please rewrite this sentence.
In lines 228-229: High OC/EC ratios larger than about 2.0 mean high SOC formation, why? The authors should rephrase this sentence to better reflect this relationship and provide supporting evidence.
In lines 243-245: Is the high average WISOC/OC ratio observed during the last two periods related to changes in weather conditions, such as wind speed?
In lines 250-252: This study used radiocarbon measurements to quantify the contributions of fossil and non-fossil sources to WSOC. I am curious why only WSOC was chosen for this analysis instead of other PM2.5 components?
In lines 259-261: A high contribution from fossil fuel sources is also likely associated with low temperatures during cold times. Rising coal combustion for cooking and heating may be a result of cold weather. Hence, I suggest that the authors refine this discussion to address the potential link between cold weather and elevated fossil fuel contributions.
In lines 275-279: This sentence is too long. Please rewrite it to make it more readable.
In lines 303-305: Change it to “…surface soil and fertilizers containing abundant potassium…”.
In lines 326: Syringic acid should be the most abundant among lignin and resin acids during heavy haze. Modify this sentence.
In lines 346-347: Remove “beneficial meteorological parameters” as it is improper to use “beneficial” in this context.
In lines 353: Enhanced biogenic emissions might be also attributable to increased wind speeds.
In lines 408-409: Anthropogenic emissions may be more appropriate here.
In lines 417-419: How does biomass burning promote the formation of biogenic SOA tracers? Is it through increasing radical concentration?
In lines 419-423: The whole sentence is too long. Besides, low levels of pinic acid during the first episode may be due to high relative humidity as well.
In lines 460-463: This is a bit confusing. The authors need to provide more evidences or references for support this conclusion. The pronounced correlations might indicate that they share similar sources, formation mechanisms, or atmospheric processing pathways.
In lines 497-498: Changing “primary vehicle exhaust emissions” to “primary emissions” may be more reasonable. The result also suggests that they are probably mainly produced in the atmosphere by the photochemical oxidation of various organic precursors.
In line 500: The authors can cite some references here. For example, the papers by Kawamura et al., 2016, Atmospheric Research. DOI: 10.1016/j.atmosres.2015.11.018
In lines 503-504: Change “secondary sources (e.g., PAHs and biogenic VOCs including …)” to “secondary sources (e.g., oxidation reactions of PAHs and biogenic VOCs …”.
In lines 510-513: The authors can find more references to support BB’s significant impact on fine particle formation. Some reports found that species released by BB can enhance radical concentration and atmospheric oxidation capacity.
In line 525: Replace “produced by …” with “from”.
In lines 542-543: This may also indicate fossil fuel sources make a dominate contribution to SOC formation during urban haze events in winter.
In lines 544-546: A large amount of fossil fuel combustion during cold periods could also contribute.
In lines 553-555: Rewrite.
Citation: https://doi.org/10.5194/egusphere-2024-2098-RC3
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