the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Jun 2022
Daily evolution of VOCs in Beijing: chemistry, emissions, transport, and policy implications
Abstract. Volatile organic compounds (VOCs) are important precursors to the formation of ozone (O3) and secondary organic aero-sols (SOA) and can also have direct human health impacts. Generally, given the range and number of VOC species, their emissions are poorly characterised. The VOC levels in Beijing during two campaigns (APHH) were investigated using a dispersion model (NAME), and a chemical box model (AtChem2) in order to understand how chemistry and transport affect the VOC concentrations in Beijing. Emissions of VOCs in Beijing and contributions from outside Beijing were modelled using the NAME dispersion model combined with the emission inventories and were used to initialize the AtChem2 box model. The modelled concentrations of VOCs from the NAME-AtChem2 combination were then compared to the output of a chemical transport model (GEOS-Chem). The results from the emission inventories and the NAME air mass pathways suggest that industrial sources to the south of Beijing and within Beijing both in summer and winter are very important in con-trolling the VOC levels in Beijing. A number of scenarios with different nitrogen oxides to ozone ratios (NOx / O3) and hydroxyl (OH) levels were simulated to determine the changes in VOC levels. In Beijing over 80 % of VOC are emitted locally during winter, while during summer about 35 % of VOC concentrations (greater for some individual species) are transported into Beijing from the surrounding regions. Most winter scenarios are in good agreement with daily GEOS-Chem simulations, with the best agreements seen for the modelled concentrations of ethanol, benzene and propane with correlation coefficients of 0.67, 0.63 and 0.64 respectively. Furthermore, the production of formaldehyde within 24 hours air travel from Beijing was investigated, and it was determined that 90 % of formaldehyde in the winter and 83 % in the summer in Beijing is secondary, produced from oxidation of non-methane volatile organic compounds (NMVOCs). The benzene / CO and toluene / CO ratios during the campaign is very similar to the ratio derived from literature for 2014 in Beijing, however more data are needed to enable investigation of more species over longer timeframes to determine whether this ratio can be applied to predicting VOCs in Beijing. The results suggest that VOC concentrations in Beijing are driven predominantly by sources within Beijing and by local atmospheric chemistry during the winter, and by a combination of transport and chemistry during the summer. Moreover, the relationship of the NOx / VOC and O3 during winter and summer shows the need for season-specific policy measures.
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AC1: 'Comment on acp-2022-379', Marios Panagi, 05 Aug 2022
There is a hidden historical error in the version used of the GEOS-Chem model which outputs the concentrations in ppb when they should be in ppb C. This error led to an incorrect comparison of GEOS-Chem with our other model that’s described in the paper. This error doesn’t affect the manuscript key results and conclusions (in fact the two models now agree more closely on the monthly averages) but some numbers in section 3.6 of the manuscript need to change. The corrections will be introduced in the manuscript along with the reviewers comments
Citation: https://doi.org/10.5194/acp-2022-379-AC1 -
RC1: 'Comment on acp-2022-379', Anonymous Referee #1, 05 Aug 2022
The manuscript by Panagi et al. investigated the levels of multiple VOC species, NOx, CO, OH during campaigns in summer and winter, provided important insights on how chemistry and transport affect the VOC concentrations in Beijing. Multiple sensitivity analyses are conducted in this work, based on a dispersion model (NAME) and a chemical box model (AtChem2) which are constrained by in-situ measurements. The analyses are comprehensive and robust, providing a feasible roadmap for future researches by combining campaign measurements, inventories, and modelling. The relationship of NOx/VOC and O3 during summer and winter indicate that season-specific policy control measures are needed
I suggest minor revisions before publication. My detailed comments are listed below.
- Line 33: GEOS-Chem is a global transport model with relatively coarse resolution (~ 0.5 degree). Comparing the modelled concentrations between NAME-AtChem2 which focus in Beijing and GEOS-Chem is not needed in the main text. You have enough interesting results to show and including such comparison doesn’t give more information. I suggest move it to SI or delete it from the manuscript.
- Line 125 – 130: It’s weird that you don’t use consistent emission inventories for all species. You mentioned that “ethylene, acetylene and ethanol emission inventories are not part of MEIC”, is it true?
- Line 141: “ethene” or “ethylene” (as shown in Line 128)? Please keep it consistent throughout the paper.
- Figure 2: How about the chemistry during transport before arriving at Beijing? The lifetime of most VOC species is less than 24 hours.
- Line 153 – 165: suggest moving this part to SI or delete it.
- Line 249 – 259: this are very interesting and valuable sensitivity test.
- Figure 6: How about formaldehyde? It’s more sensitive to chemistry. Please add similar plots for formaldehyde.
- Figure 8: Poor correlations between OVOCs and NOx in the model. Any reasons for this bias?
- Line 463 – 465: Worst performance for S5 by constraining OH is found compared to other cases. Can I interpret it in this way, constraining OH is NOT a good option for further box modeling?
- Line 476 – 478: I don’t quite understand this statement. Reducing VOC will decrease formaldehyde, and then further decrease ozone formation, right?
- Line 481 – 484: You mean in winter, it's in transition regime, and in summer, it's VOC limited? Can you explain more on this? Also, in summer, the biogenic VOC emissions can play a key role. How will isoprene emissions in summer affect your conclusion?
Citation: https://doi.org/10.5194/acp-2022-379-RC1 -
AC2: 'Reply on RC1', Marios Panagi, 05 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-379/acp-2022-379-AC2-supplement.pdf
-
RC2: 'Comment on acp-2022-379', Anonymous Referee #2, 13 Oct 2022
This manuscript focused on ambient VOC measurements in Beijing, and investigated the local and regional contributions, as well as photochemical effects on VOC concentrations in Beijing through modelling approaches. The study is of interest to the atmospheric community and suitable for publication in ACP. However, there are not many new insights from the analysis, and the discussion in the manuscript is not enough to give a full picture of the VOC chemistry, sources, transport, and control policies in Beijing as the authors claimed in the title. Besides, some conclusions in this study are inaccuracy. Moreover, the manuscript is not well-organized, and suffers from many flaws especially the language expression. Overall, the quality of the manuscript does not reach the standard for publication in ACP in current state. A revised edition is encouraged for resubmission. Some detailed comments are provided for the authors as follows:
- How many VOC species were detected by GC-FID? Could you present detailed observation data? In the manuscript, only limited species were listed and used for comparison with modelling results. Better to use more species if there were.
- The method used to estimate OFP is irrational. The VOCs measured in the ambient are already reacted. Since the OH concentration in summer is usually higher than that in winter, the photooxidation is more reactive in summer and thus in general higher O3 production. One should use corrected VOC concentrations to calculate OFP, otherwise will lead to wrong conclusion.
- What’s the uncertainty of modelling results in this study? In Table 1, the variations in modelled VOC concentrations are small among different scenarios. It’s difficult to tell they are real changes due to different settings.
- L64-67. I do not clearly understand this sentence. But according to Gu et al. (2019), the concentrations of NMVOCs in winter polluted days were highest, followed by summer polluted days, summer normal days, and winter normal days.
- From my side, It seems better to put the description of VOC/CO ratio (Sect. 3.1), the region division for NAME (in Sect. 3.2), and the scenarios description (in Sect. 3.3) to Sect. 2.
- What does APHH VOC/CO * CO APHH mean in Fig.3? In my understanding, APHH VOC/CO * CO APHH = VOC APHH.
- L223-225: “During the summer campaign, … to the 20% that was observed in the winter.” It’s difficult to understand this statement.
- Fig.9: Poor correlation between NOx and VOCs for both measured and modelled data. What’s the reason? Do you have any explanations?
Citation: https://doi.org/10.5194/acp-2022-379-RC2 -
AC3: 'Reply on RC2', Marios Panagi, 05 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-379/acp-2022-379-AC3-supplement.pdf
Status: closed
-
AC1: 'Comment on acp-2022-379', Marios Panagi, 05 Aug 2022
There is a hidden historical error in the version used of the GEOS-Chem model which outputs the concentrations in ppb when they should be in ppb C. This error led to an incorrect comparison of GEOS-Chem with our other model that’s described in the paper. This error doesn’t affect the manuscript key results and conclusions (in fact the two models now agree more closely on the monthly averages) but some numbers in section 3.6 of the manuscript need to change. The corrections will be introduced in the manuscript along with the reviewers comments
Citation: https://doi.org/10.5194/acp-2022-379-AC1 -
RC1: 'Comment on acp-2022-379', Anonymous Referee #1, 05 Aug 2022
The manuscript by Panagi et al. investigated the levels of multiple VOC species, NOx, CO, OH during campaigns in summer and winter, provided important insights on how chemistry and transport affect the VOC concentrations in Beijing. Multiple sensitivity analyses are conducted in this work, based on a dispersion model (NAME) and a chemical box model (AtChem2) which are constrained by in-situ measurements. The analyses are comprehensive and robust, providing a feasible roadmap for future researches by combining campaign measurements, inventories, and modelling. The relationship of NOx/VOC and O3 during summer and winter indicate that season-specific policy control measures are needed
I suggest minor revisions before publication. My detailed comments are listed below.
- Line 33: GEOS-Chem is a global transport model with relatively coarse resolution (~ 0.5 degree). Comparing the modelled concentrations between NAME-AtChem2 which focus in Beijing and GEOS-Chem is not needed in the main text. You have enough interesting results to show and including such comparison doesn’t give more information. I suggest move it to SI or delete it from the manuscript.
- Line 125 – 130: It’s weird that you don’t use consistent emission inventories for all species. You mentioned that “ethylene, acetylene and ethanol emission inventories are not part of MEIC”, is it true?
- Line 141: “ethene” or “ethylene” (as shown in Line 128)? Please keep it consistent throughout the paper.
- Figure 2: How about the chemistry during transport before arriving at Beijing? The lifetime of most VOC species is less than 24 hours.
- Line 153 – 165: suggest moving this part to SI or delete it.
- Line 249 – 259: this are very interesting and valuable sensitivity test.
- Figure 6: How about formaldehyde? It’s more sensitive to chemistry. Please add similar plots for formaldehyde.
- Figure 8: Poor correlations between OVOCs and NOx in the model. Any reasons for this bias?
- Line 463 – 465: Worst performance for S5 by constraining OH is found compared to other cases. Can I interpret it in this way, constraining OH is NOT a good option for further box modeling?
- Line 476 – 478: I don’t quite understand this statement. Reducing VOC will decrease formaldehyde, and then further decrease ozone formation, right?
- Line 481 – 484: You mean in winter, it's in transition regime, and in summer, it's VOC limited? Can you explain more on this? Also, in summer, the biogenic VOC emissions can play a key role. How will isoprene emissions in summer affect your conclusion?
Citation: https://doi.org/10.5194/acp-2022-379-RC1 -
AC2: 'Reply on RC1', Marios Panagi, 05 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-379/acp-2022-379-AC2-supplement.pdf
-
RC2: 'Comment on acp-2022-379', Anonymous Referee #2, 13 Oct 2022
This manuscript focused on ambient VOC measurements in Beijing, and investigated the local and regional contributions, as well as photochemical effects on VOC concentrations in Beijing through modelling approaches. The study is of interest to the atmospheric community and suitable for publication in ACP. However, there are not many new insights from the analysis, and the discussion in the manuscript is not enough to give a full picture of the VOC chemistry, sources, transport, and control policies in Beijing as the authors claimed in the title. Besides, some conclusions in this study are inaccuracy. Moreover, the manuscript is not well-organized, and suffers from many flaws especially the language expression. Overall, the quality of the manuscript does not reach the standard for publication in ACP in current state. A revised edition is encouraged for resubmission. Some detailed comments are provided for the authors as follows:
- How many VOC species were detected by GC-FID? Could you present detailed observation data? In the manuscript, only limited species were listed and used for comparison with modelling results. Better to use more species if there were.
- The method used to estimate OFP is irrational. The VOCs measured in the ambient are already reacted. Since the OH concentration in summer is usually higher than that in winter, the photooxidation is more reactive in summer and thus in general higher O3 production. One should use corrected VOC concentrations to calculate OFP, otherwise will lead to wrong conclusion.
- What’s the uncertainty of modelling results in this study? In Table 1, the variations in modelled VOC concentrations are small among different scenarios. It’s difficult to tell they are real changes due to different settings.
- L64-67. I do not clearly understand this sentence. But according to Gu et al. (2019), the concentrations of NMVOCs in winter polluted days were highest, followed by summer polluted days, summer normal days, and winter normal days.
- From my side, It seems better to put the description of VOC/CO ratio (Sect. 3.1), the region division for NAME (in Sect. 3.2), and the scenarios description (in Sect. 3.3) to Sect. 2.
- What does APHH VOC/CO * CO APHH mean in Fig.3? In my understanding, APHH VOC/CO * CO APHH = VOC APHH.
- L223-225: “During the summer campaign, … to the 20% that was observed in the winter.” It’s difficult to understand this statement.
- Fig.9: Poor correlation between NOx and VOCs for both measured and modelled data. What’s the reason? Do you have any explanations?
Citation: https://doi.org/10.5194/acp-2022-379-RC2 -
AC3: 'Reply on RC2', Marios Panagi, 05 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-379/acp-2022-379-AC3-supplement.pdf
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