An Ozone “Pool” in South China: Investigations on Atmospheric Dynamics and Photochemical Processes Over the Pearl River Estuary

Abstract

Pearl River Estuary (PRE) has been recognized as one of the key areas in South China experiencing severe air pollution. To understand the photochemical pollution over PRE, intensive measurements of O 3 and its precursors were simultaneously conducted at a suburban site on the east bank of PRE (Tung Chung, TC) in Hong Kong and a rural site on the west bank (Qi'ao Island, QAI) in Zhuhai from 25 September to 29 November 2016. Three and sixteen O 3 episode days (days with the maximum hourly O 3 higher than 100 ppbv) were captured at TC and QAI, respectively. On the three days when O 3 episodes occurred at TC, QAI also suffered from O 3 episodes, which were all associated with tropical cyclones (typhoons). As a downwind site of PRE when northwesterly winds prevailed, TC displayed a higher maximum hourly O 3 than QAI on these three days. In contrast, the other thirteen episodes that solely occurred at QAI were generally under northeasterly winds, which brought more coastal air to TC and led to lower levels of O 3 at this site. In addition, the stronger titration of the locally emitted NO to O 3 also accounted for the lower O 3 at TC on these days. The simulations by Weather Research and Forecasting coupled with Chemistry model indicated that the interactions of synoptic winds and mesoscale breezes led to relatively weak winds and long residence time for air pollutants over the PRE, thereby air pollution accumulation. This provided the likelihood of intensive chemical productions of O 3 over PRE, with the production rates even higher than those in the surrounding land areas. As such, it was concluded that PRE was a "pool" of O 3 , where atmospheric dynamics caused the accumulation of air pollutants and subsequently intensive photochemical reactions. The findings in this study may also apply to the other estuaries connecting terrestrial and marine systems over the world.

Role of Heat Wave‐Induced Biogenic VOC Enhancements in Persistent Ozone Episodes Formation in Pearl River Delta

“…Although all sites showed good agreement with the observations, the peak values of O 3 concentration in GZ, ZQ, and DG during the O 3 episode were slightly underestimated. In the case of NO 2 , despite large bias existed in the WCR, the variations of NO 2 in most sites are well captured by the CMAQ simulation with IOA ranging from 0.52 to 0.71 and NMB values between 0.30 and 0.47, which were within the range (0.40–0.70) of acceptable model performance in literature (Wang et al., 2015; Zeren et al., 2019). These biases for O 3 and NO 2 are comparable with other modeling studies in PRD that have identified the uncertainty in emission inventory and bias in meteorological fields as primary causes (Hu et al., 2016; Ou et al., 2016; Wang et al., 2010).…”

Atmospheric oxidation capacity and ozone pollution mechanism in a coastal city of southeastern China: analysis of a typical photochemical episode by an observation-based model

“…The reduction of observed O 3 ( O 3 ) in the early morning rush hour caused by NO titration did not appear, verifying the impacts of regional transport (X. Zeren et al, 2019;Chen et al, 2020). Due to the photochemical reactions, the precursors of CO, NO x , and VOCs were consumed during the daytime and were accumulated during the nighttime with weak solar radiation.…”

Key Points in Air Pollution Meteorology

“…Batchvarova et al [ 47 ] measured aerosol concentration at Ahtopol (Bulgaria) and found a lower number of coarse particles for marine air masses. Another example is the Pearl River Delta, where interactions of synoptic winds and mesoscale breezes determined weak winds and air pollution accumulation, favouring intense photochemical reactions and the formation of an ozone “pool” [ 48 ]. Similarly, in Manila, Philippines, strong sea breezes disperse fine particulate matter inland during the day in spring, although breezes are the outflow path of these aerosols during the night.…”