1Institute for Environmental and Climate Research, Jinan University, Guangzhou, 511443, China
2Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical Weather Prediction, China Meteorological Administration, Guangzhou 510640, China
3Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, 511443, China
4Guangdong Ecological Meteorology Center (Pearl River Delta Center for Environmental Meteorology Prediction and Warning), Guangzhou 510640, China
5School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
1Institute for Environmental and Climate Research, Jinan University, Guangzhou, 511443, China
2Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical Weather Prediction, China Meteorological Administration, Guangzhou 510640, China
3Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, 511443, China
4Guangdong Ecological Meteorology Center (Pearl River Delta Center for Environmental Meteorology Prediction and Warning), Guangzhou 510640, China
5School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
Received: 17 Apr 2022 – Discussion started: 24 May 2022
Abstract. A record-breaking severe ozone (O3) pollution episode occurred in the Pearl River Delta (PRD) in early Autumn 2019 when PRD was under the influence of a Pacific subtropical high followed by Typhoon Mina. In this study, we analyzed the effects of meteorological and photochemical processes on the O3 concentration in PRD during this episode by carrying out the Weather Research Forecast-Community Multiscale Air Quality (WRF-CMAQ) model simulations. Results showed that low relative humidity, high boundary layer height, northerly surface winds and strong downdrafts were the main meteorological factors contributing to O3 pollution. Moreover, delayed sea breezes that lasted into the night would transport O3 from the sea back to land and resulted in secondary O3 maxima at night. In addition, O3 and its precursors stored in the residual layer above the surface layer at night can be mixed down to the surface in the next morning, further enhancing the daytime ground-level O3 concentration the following day. Photochemical production of O3, with daytime average production rate of about 7.2 ppb/h, is found to be the predominate positive contributor to the O3 budget of the boundary layer (0–1260 m) during the entire O3 episode; while the horizontal and vertical transport fluxes are the dominant negative contributors. This O3 episode accounted for 10 out of the yearly total of 51 days when the maximum daily 8-h average (MDA8) O3 concentrations exceeded the national standard of 75 ppb in PRD in 2019. Based on these results, we propose that the enhanced photochemical production of O3 during the episode is a major cause of the most severe O3 pollution year since the official O3 observation started in PRD in 2006. Moreover, since this O3 episode is a synoptic scale phenomenon covering the entire eastern China, we also suggest that the enhanced photochemical production of O3 in this O3 episode is a major cause of the extraordinary high O3 concentrations observed in eastern China in 2019.
The manuscript entitled “Impact of a subtropical high and a typhoon on a severe ozone pollution episode in the Pearl River Delta, China” by Shanshan Ouyang et al. explored in details how the severe O3 pollution in PRD is influenced by the weather system of subtropical high and typhoon. The manuscript provides valuable information for understanding the ozone pollution formation mechanism in coastal areas, and is well within the scope of ACP. I only have the following minor comments needed to be addressed before the publication.
General comments
One of the major findings of this manuscript is that the photochemical O3 production is enhanced during the influence of subtropical high and typhoon, and acts a major cause of the most severe O3 pollution in PRD. However, why the photochemistry process is enhanced during the two events is not clearly discussed. Especially, How the enhanced photochemistry related to changed meteorological factors? Although the meteorological factors and photochemical process are separately discussed, there are inner relationship between meteorological factors and photochemical process. I suggest to further elucidate how the changes in meteorological factors induced by typhoon and the subtropical high influences the photochemical production of ozone.
Specific comments
Line 114: Is the O3 concentration corresponding to the simulated O3 in the lowest layer (i.e., below 35 m)? If take the lowest 3 layers into account, especially for periods strongly influenced by downdraft, what would the comparison between the model simulation and the observation look like?
Line 115: Please define “NAWO” and “CNMC”. Is CNMC the same as NEMC in Line 76? If so, please keep the abbreviation consistent.
Line 133: Please add description on “the second standard of air quality”.
Line 137 - 138: Please define “Lev 3” and “Lev 5”.
Line 173: The model overestimated WS10 quite a lot. Which of the wind vector (i.e., u, v, ω) has not been well reproduced that could lead to the WS10 overestimation? How would this overestimation further influence the evaluation of the contribution of transport / sea breeze?
Line 189: Please define U10, V10.
Line 210: Please define θv.
Line 213 - 216: Higher PBLH could result in higher O3 concentration due to enhanced contribution of downward O3transport. However, higher PBLH could also favor the dilution of O3 and its precursors, thus result in weaker O3production and accumulation. What would be the balance between these two effects?
Figure 5: It looks like there is a 1-hour time shift between the simulated and the observed O3 concentration. This could be caused by the definition of the measurement time of the CNEC O3 data (i.e., data at 1:00 represent the averages in 0:00 – 1:00). If this time shift has been taken into account, would the discrepancy between the simulation and the observation become smaller?
Figure 11b: Do the individual processes correspond to the averages of whole boundary layer?
A record-breaking severe O3 pollution episode occurred under the influence of a Pacific subtropical high followed by Typhoon Mina in the Pearl River Delta (PRD) in early Autumn 2019. Through the WRF-CMAQ model simulations, we propose that the enhanced photochemical production of O3 during the episode is a major cause of the most severe O3 pollution year since the official O3 observation started in PRD in 2006.
A record-breaking severe O3 pollution episode occurred under the influence of a Pacific...
