Observation-based Analysis of Ozone Production Sensitivity for Two Persistent Ozone Episodes in Guangdong, China

Song, Kaixiang; Liu, Run; Wang, Yu; Liu, Tao; Wei, Liyan; Wu, Yanxing; Zheng, Junyu; Wang, Boguang; Liu, Shaw Chen

doi:https://doi.org/10.5194/acp-2022-50

Preprints

https://doi.org/10.5194/acp-2022-50

Preprints

24 Jan 2022

Status: a revised version of this preprint is currently under review for the journal ACP.

Observation-based Analysis of Ozone Production Sensitivity for Two Persistent Ozone Episodes in Guangdong, China

Kaixiang Song¹, Run Liu^1,2, Yu Wang^1,2, Tao Liu¹, Liyan Wei¹, Yanxing Wu¹, Junyu Zheng^1,2, Boguang Wang^1,2, and Shaw Chen Liu^1,2 Kaixiang Song et al.

Show author details

¹Institute for Environmental and Climate Research, Jinan University, Guangzhou, 511443, China
²Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, 511443, China

Received: 18 Jan 2022 – Discussion started: 24 Jan 2022

Abstract. An observation-based method (OBM) is developed to investigate the sensitivity of ozone formation to precursors during two persistent elevated ozone episodes observed at 77 stations in Guangdong. Average OH concentrations derived at the 77 stations between 08:00 and 13:00 local time stay within a narrow range of 2.5 × 10⁶ cm⁻³ to 5.5 × 10⁶ cm⁻³ with a weak dependence on the NOx. These values are in good agreement with OH values observed at a rural station in Pearl River Delta (PRD) and a box model constrained by the ambient conditions. They also agree well with a box model constrained by the ambient conditions observed during the two episodes. The OBM has been used to evaluate the ozone production efficiency, ε(NO_x or VOC), defined as the number of O₃ molecules produced per molecule of NO_x (or VOC) oxidized. Average values of ε(NO_x) and ε(VOC) determined by the OBM are 3 and 2.1 ppb/ppb, respectively, both compared well with values in previous studies. Approximately 67 % of the station-days exhibit ozone formation sensitivity to NO_x, approximately 20 % of the station-days are in the transitional regime sensitive to both NO_x and VOC, only approximately 13 % of the station-days are sensitive to VOC. These results are in semi-quantitative agreement with the ozone formation sensitivity calculated by the box model constrained by ambient conditions observed during the two episodes. However, our OBM results differ from those of most previous investigations which suggested that limiting the emission of VOC rather than NO_x would be more effective in reducing ozone reduction in Guangdong.

Download & links

Preprint (PDF, 1637 KB)

Supplement (228 KB)

Kaixiang Song et al.

Status: final response (author comments only)

RC1:
'Comment on acp-2022-50', Anonymous Referee #1, 17 Mar 2022
The authors developed an observation-based method to investigate the ozone production efficiency and ozone production sensitivity to precursors for two persistent ozone episodes in Guangdong, China, based on the hourly surface O₃, PM_2.5, CO and NO₂ data at 77 stations in Guangdong during the period 2018-2019. They also performed a box model constrained by ambient conditions observed during the two episodes for comparison. They find 67% of the station-days exhibit ozone formation sensitivity to NOx, which differs from other previous studies which suggested that limiting VOC emission rather than NOx would be more effective in reducing ozone in Guangdong, and these results are in semi-quantitative agreement with the results calculated by box model. The authors make some arbitrary assumptions and simplifications in derivations of VOC and OH concentrations, which is a major weakness of the current work. I had a number of specific comments for the authors to consider and address before publication.

Specific comments:

Specific information on the ratios of VOC/CO that is used in this study for the derivation of VOC is better added in the SI. Also, the uncertainties due to this treatment of VOC on OH concentration should be discussed.

Line 80-81, the author uses the same way to evaluate the leftover VOC as to evaluate the leftover CO in the following day. However, VOCs can continue to be oxidized by OH and NO₃ in the afternoon and at night. How great are the effects of this neglect of the depletion of leftover VOC on the derived VOC and OH concentrations in the following day?

Line 81-82, the authors state that the oxidized VOC are estimated from the observed ratios of HCHO, CH₃CHO, and ketone to CO in Wang et al., 2016, and other OVOCs are not included. What is the basis for this treatment? Besides, HCHO, CH₃CHO, and ketone are not only photochemical products of VOC oxidation but also from direct anthropogenic emission. How do the authors deal with the difference in emission-related origin of OVOC among different locations? Given that OVOCs typically make large portion of OH reactivity, the estimations of OVOCs are crucial for the simulation of OH concentrations. How large are the uncertainties of these assumption on the predicted OH concentrations?

Line 85-112, the derivation of OH concentrations and calculation of oxidized VOC and NOx in this study are all based on the Lagrangian condition assumption, which rarely exists in the real atmosphere, so the authors make a selection criterion to filter out days satisfy the quasi-Lagrangian condition. What is the basis of this selection criterion?

Line 122-126, why the product of the average OH at noontime and the mean NOx in 13:00-16:00 can be used as the hourly NOx emission rate between 08:00 and 13:00?

Line 311-315, these sentences are totally a copy of the sentences in line 78-83, and do not provide any useful information, and I would like to suggest the authors to delete these sentences, and provide more useful information about the uncertainty analysis.

I would like to suggest the authors can review other literatures reporting the ozone production efficiency in PRD areas to strengthen the discussion.

Considering that all the VOCs data are estimated based on the ratios of VOC/CO in the emission inventory, I think it is not appropriate to name it an observation-based method.
Citation: https://doi.org/10.5194/acp-2022-50-RC1
- AC1: 'Reply on RC1', Run Liu, 22 May 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-50/acp-2022-50-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-50-AC1
RC2:
'Comment on acp-2022-50', Anonymous Referee #2, 10 Apr 2022
Observation-based Analysis of Ozone Production Sensitivity for Two Persistent Ozone Episodes in Guangdong, China

In this paper by Song et al., the authors use 2 episodes in Guangdong, China and a large number of measurement sites in the vicinity to construct an observation-based method (OBM), utilizing the measurements of various pollutants from said sites alongside a box model based on the CB05 chemical mechanism, with the purpose of determining ozone production efficiency (OPE) from NO_x and VOCs. They conclude that the area is under a NO_x limited regime, indicating that limiting NO_xemissions is the optimal strategy to reduce ozone formation in the area, contrary to previous studies.

While the paper does have its strong points – the analysis is thorough, the English used is clear and appropriate – it is not without shortcomings, many of which reviewer #1 covered. The paper merits publication based on the rigor of its analysis, but not that of the conclusions. As such I recommend the paper for publication only after the following points have been addressed and the discussion strengthened.

Science comments

As the authors mention two episodes are not enough. In addition, they are well into the ozone season in the fall, which could further bias the results. For example, biogenic emissions of VOCs are going to be significantly less than what they would be during the summertime, which could tip the balance of the OPE. A section should be added to discuss the potential differences between summer and fall months. The box model the authors have developed can be used, driven with meteorological variables from the observation sites during different seasons (if available), to investigate

Based on (1), the usage of CO to VOC ratios, while a valid strategy for anthropogenic emissions completely neglects possible biogenic impacts and thus is better suited towards the urban sites much more than the rural sites. In addition to the current analysis, it would be of value that the authors also conduct the same by splitting the sites in rural and urban which would be more representative

I second reviewer’s #1 comment about the NOx quasi steady state. This would only apply from 13:00 to 16:00. Using the average OH value for the early day is not accurate

The calculation of OPE assumes that the only real sink of NO_x is the ozone formative chemistry. However, NO_xis also lost to other processes and in an area like deposition and nitrate formation. The deposition is briefly mentioned towards the end, but some additional discussion and/or an estimate of the magnitude of the effect should be provided. Given the close proximity of ports in the area and therefore the likely high emissions of SO₂ and subsequent sulfate formation, the additional NO_x sinks could be of an important magnitude. I do realize that such an analysis would be out of the scope of the paper, and I do not require that authors conduct it, but some additional discussion on the matter is warranted, given the number of assumptions already used. On that note, particularities of Guangdong should be added to the introduction e.g., nearby ports, major highways, nearby agricultural activities etc.

Editorial comments

The timeseries of meteorological parameters is more suited for the SI. Use the diurnal profiles instead in the manuscript, so the reader can directly go back and forth with the diurnal concentrations to clearly see the dilution effect due to the PBL

While I do understand why Figure 8 was added, and it holds a lot of valuable information, it would be best to either omit it or add it to the SI. Figure 9 is more appropriate, and it would be even better if you turn it into 2D plots with variable marker sites

The combined site isopleth could use some polishing; fill out the contours. Also, I very strongly recommend that you make isopleth for each of the observation site clusters from Figure 1. This also feeds into point 2 from the science comments above
Citation: https://doi.org/10.5194/acp-2022-50-RC2
- AC2: 'Reply on RC2', Run Liu, 22 May 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-50/acp-2022-50-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-50-AC2

Kaixiang Song et al.

Supplement

https://doi.org/10.5194/acp-2022-50-supplement

Kaixiang Song et al.

Viewed

Total article views: 349 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
240	91	18	349	25	6	10

HTML: 240
PDF: 91
XML: 18
Total: 349
Supplement: 25
BibTeX: 6
EndNote: 10

Views and downloads (calculated since 24 Jan 2022)

Month	HTML	PDF	XML	Total
Jan 2022	52	25	4	81
Feb 2022	71	23	4	98
Mar 2022	53	20	2	75
Apr 2022	29	11	3	43
May 2022	35	12	5	52

Cumulative views and downloads (calculated since 24 Jan 2022)

Month	HTML	PDF	XML	Total
Jan 2022	52	25	4	81
Feb 2022	71	23	4	98
Mar 2022	53	20	2	75
Apr 2022	29	11	3	43
May 2022	35	12	5	52

Viewed (geographical distribution)

Total article views: 511 (including HTML, PDF, and XML) Thereof 511 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 26 May 2022

Short summary

We developed an observation-based method to investigate the sensitivity of ozone formation to precursors during two elevated ozone episodes observed at 77 stations in Guangdong, China. We found approximately 67 % of the station-days exhibit ozone formation sensitivity to NO_x, 20 % of the station-days are in the transitional regime sensitive to both NO_x and VOC, only 13 % of the station-days are sensitive to VOC.


Total:	0
HTML:	0
PDF:	0
XML:	0