North China Plain as a hot spot of ozone pollution exacerbated by extreme high temperatures

Parrish²,

et al. 2022

Atmos. Chem. Phys.

Abstract. In the past decade, ozone (O3) pollution has become a severe environmental problem in China's major cities. Here, based on available observational records, we investigated the long-term trend of O3 pollution in China during 2014–2020. The O3 concentrations were slightly higher in urban areas than in non-urban areas. During these 7 years, the highest O3 concentrations primarily occurred during summer in northern China, and during autumn or spring in southern China. Although O3 precursors, including nitrogen oxides (NOx) and carbon monoxide (CO), continuously decreased, O3 concentrations generally increased throughout the 7 years with a slower increasing rate after 2017. The long-term trend of O3 concentrations differed across seasons, especially from 2019 to 2020, when O3 concentrations decreased in summer and increased in winter. To analyse the causes of this observed trend, a photochemical box model was used to investigate the change in the O3 sensitivity regime in two representative cities – Beijing and Shanghai. Our model simulations suggest that the summertime O3 sensitivity regime in urban areas of China has changed from a VOC-limited regime to a transition regime during 2014–2020. By 2020, the urban photochemistry was in a transition regime in summer but in a VOC-limited regime in winter. This study helps to understand the distinct trends of O3 in China and provides insights into efficient future O3 control strategies in different regions and seasons.

Section: Resultsmentioning

confidence: 99%

Long-term trend of ozone pollution in China during 2014–2020: distinct seasonal and spatial characteristics and ozone sensitivity

Parrish²,

et al. 2022

Atmos. Chem. Phys.

“…Therefore, our simulations may underestimate surface O 3 concentrations under carbon neutrality scenario, because high air temperature can increase natural emissions (e.g. BVOC and soil NOx) (Lu et al 2021, Lei et al 2022 and accelerate photochemical reactions (Pyrgou et al 2018, Wang et al 2022 In this study, we only consider biogeochemical processes, including stomatal uptake and BVOC emissions to assess the impacts of terrestrial vegetation on surface O 3 , mainly because the feedback of vegetation on meteorology is not coupled in the GEOS-Chem model. Previous studies have showed that vegetation can decrease surface temperature and increase atmospheric relative humidity through transpiration (Mahmood et al 2014, Yu et al 2020.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Impacts of terrestrial vegetation on surface ozone in China: from present to carbon neutrality

Lei,

Yue,

Wang

et al. 2024

Environ. Res. Lett.

Despite many efforts to control anthropogenic sources, high ambient ozone (O3) concentrations remain a serious air pollution problem in China. Terrestrial vegetation can remove surface O3 through dry deposition but also enhance surface O3 through biogenic volatile organic compound (BVOC) emissions. However, the net impacts of terrestrial vegetation on surface O3 remains unclear. Here, we perform simulations using a chemistry-vegetation coupled model to assess the impacts of terrestrial vegetation on surface daily maximum 8 h average (MDA8) O3 in China through biogeochemical processes, including BVOC emissions and stomatal uptake. The results show that vegetation biogeochemical processes increase summer mean surface MDA8 O3 by 1.3 ppb in the present day in China, with 3.7 ppb from BVOC emissions but -2.7 ppb from stomatal uptake. However, the enhanced summer mean surface MDA8 O3 from vegetation biogeochemical processes decreases from 5.4 to 2.7 ppb in the North China Plain (NCP), from 7.2 to 0.8 ppb in the Yangtze River Delta (YRD), from 8.7 to 1.8 ppb in the Sichuan Basin (SCB) and from 4.2 to 0.4 ppb in the Pearl River Delta (PRD) by the period of carbon neutrality. Our study highlights that carbon neutrality-driven emission reductions can greatly mitigate the enhanced surface O3 related to terrestrial vegetation, though there is still a positive impact of terrestrial vegetation on surface O3 in some hotspots, including the NCP and the SCB.

“…After COVID-19 lockdown period, the decreasing trend of NOx (59%) was much higher than that of TVOCs (41), which aggravated the rebound of O3 concentration. In addition, the increased P might exacerbate O3 pollution though T remained stable during COVID-19 period (Chen et al, 2019;Dong et al, 2020;Wang et al, 2022).…”

Section: Overview Of Observationsmentioning

confidence: 99%

The impact of COVID-19 lockdown on ozone budget and radical chemistry in a typical industrial city of China

Cui

2023

Preprint

Ozone (O) levels in East China suffered from rapid increases during the COVID-19 period. To clarify the reason for the O increase, a continuous campaign was performed in a industrial city in North China Plain (NCP). Meanwhile, the machine-learning technique and the box model were employed to reveal the mechanisms of O increase from the perspective of meteorology and photochemical process, respectively. The result suggested that the ambient O level in Tangshan increased from 18.7 ± 4.63 to 45.6 ± 8.52 μg/m (143%) after COVID-19 lockdown, and the emission reduction and meteorology contributed to 77% and 66% of this increment, respectively. The higher Wind speed (WS) coupled with regional transport played a significant role on O increase (30.8 kg/s). The O sensitivity verified that O production was highly volatile organic compounds (VOC)-sensitive (Relative incremental reactivity (RIR): 0.75), while the NO showed the negative impact on O production in Tangshan (RIR: -0.59). It suggested that the control of VOCs rather than NO might be more effective in reducing O level in Tangshan because it was located on the VOC-limited regime. Besides, both of ozone formation potential (OFP) analysis and observation-based model (OBM) demonstrated that the alkenes (36.3 ppb) and anthropogenic oxygenated volatile organic compounds (OVOCs) (15.2 ppb) showed the higher OFP compared with other species, and their reactions released a large number of HO and RO radicals. Moreover, the concentrations of these species did not experience marked decreases after COVID-19 lockdown, which were major contributors to O increase during this period.