Measurement and model analyses of the ozone variation during 2006 to 2015 and its response to emission change in megacity Shanghai, China

Abstract

The fine particles (PM 2.5 ) in China have decreased significantly in recent years as a result of the implementation of Chinese Clean Air Action Plan since 2013, while the O 3 pollution is getting worse, especially in megacities such as Beijing and Shanghai. Better understanding of the elevated O 3 pollution in Chinese megacities and its response to emission change is important for developing an effective emission control strategy in the future. In this study, we analyze the significant increasing trend of daily maximum O 3 concentration from 2006 to 2015 in the megacity Shanghai with the variability of 0.8-1.3 ppbv yr −1 . It could likely be attributed to the notable reduction in NO x concentrations with the decreasing rate of 1.86-2.15 ppbv yr −1 accompanied by the small change in VOCs during the same period by excluding the weak trends of meteorological impacts on local dispersion (wind speed), regional transport (wind direction), and O 3 photolysis (solar radiation). It is further illustrated by using a state-of-the-art regional chemical and dynamical model (WRF-Chem) to explore the O 3 variation response to the reduction in NO x emissions in Shanghai. The control experiment conducted for September of 2009 shows excellent performance for O 3 and NO x simulations, including both the spatial distribution pattern and the day-by-day variation through comparison with six in situ measurements from the MIRAGE-Shanghai field campaign. Sensitivity experiments with 30 % reduction in NO x emissions from 2009 to 2015 in Shanghai estimated by Shanghai Environmental Monitoring Center shows that the calculated O 3 concentrations exhibit obvious enhancement by 4-7 ppbv in urban zones with increasing variability of 0.96-1.06 ppbv yr −1 , which is consistent with the observed O 3 trend as a result of the strong VOC-limited condition for O 3 production. The large reduction in NO x combined with less change in VOCs in the past 10 years promotes the O 3 production in Shanghai to move towards an NO x -limited regime. Further analysis of the WRF-Chem experiments and O 3 isopleth diagram suggests that the O 3 production downtown is still under a VOC-limited regime after 2015 despite the remarkable NO x reduction, while it moves to the transition regime between NO x -limited and VOC-limited in sub-urban zones. Supposing the insignificant VOC variation persists, the O 3 concentration downtown would keep increasing until 2020 with the further 20 % reduction in NO x emission after 2015 estimated by Shanghai Clean Air Action Plan. The O 3 production in Shanghai will switch from a VOC-limited to an NO x -limited regime after 2020 except for downtown area, which is likely close to the transition regime. As a result the O 3 concentration will decrease by 2-3 ppbv in sub-urban zones and by more than 4 ppbv in rural areas as a response to a 20 % reduction in NO x emission after 2020, whereas it is not sensitive to both NO x and VOC changes downtown. This result reveals that Published by Copernicus Publications on behalf of the European Geosci...

Observationally constrained modeling of atmospheric oxidation capacity and photochemical reactivity in Shanghai, China

“…Both the removal of these O 3 precursors, such as methane (CH 4 ), non-methane volatile organic compounds (NMVOCs), carbon monoxide (CO) and NO x , and the formation of secondary pollutants like ozone and secondary organic/inorganic aerosols are controlled by the oxidation capacity of the atmosphere (Prinn, 2003;Hofzumahaus et al, 2009;Ma et al, 2010Ma et al, , 2012Feng et al, 2019). The term "atmospheric oxidation capacity (AOC)" is defined as the sum of the respective oxidation rates of primary pollutants (CH 4 , NMVOCs and CO) by the oxidants (OH, O 3 and NO 3 ; Elshorbany et al, 2009;Xue et al, 2016). Therefore, understanding the processes and rates under which these species are oxidized in the atmosphere is critical to identify the controlling factors of secondary pollution in the atmosphere.…”

“…High temperature and high radiation promote HO x cycling reactions, which is also affected by the abundance of other atmospheric compounds (Coates et al, 2016;Xing et al, 2017). This cycling is closely related to atmospheric photochemical reactivity, especially the generation of ozone, secondary aerosols and other pollutants (Mao et al, 2010;Xue et al, 2016). The radical cycling is terminated by their crossreactions with NO x under high-NO x conditions (e.g., OH + NO 2 , RO 2 + NO and RO 2 + NO 2 ) and RO x under low-NO x conditions (e.g., HO 2 + HO 2 , RO 2 + HO 2 and RO 2 + RO 2 ), which results in the formation of nitric acid, organic nitrates and peroxides (Wood et al, 2009;Liu et al, 2012;Xue et al, 2016).…”

Land cover change dominates decadal trends of biogenic volatile organic compound (BVOC) emission in China

“…China has initiated a series of pollution control policies in recent years (Zheng et al, 2018;Ma et al, 2019) and achieved success in controlling some air pollutants, especially PM2.5 Yu et al, 2019;Xu et al, 2019). However, the ozone pollution is still severe in China especially the mega-city areas (Li et al, 2019;Xu et al, 2019). It is widely known that NOx and VOC are the precursors of ground 5 level ozone pollution (Seinfeld and Pandis, 2012).…”

“…We used the long-term record of satellite HCHO VC from the OMI sensor to asses our estimation of The increase of BVOC reported by this study is expected to lead to a more complex situation for making the policies for controlling ozone pollution in China. The recent pollution control policies in China have effectively initiated the control of PM2.5 pollution, but the ozone pollution is still severe especially in 5 urban areas Yu et al, 2019;Xu et al, 2019;Li et al, 2019). Although anthropogenic emission is still the dominant source of NMVOC in China and is ~70 % higher than the average biogenic emission in China, the BVOC still makes an important contribution to ozone pollution in mega cities including Beijing (Pang et al, 2009;Shao et al, 2009), Shang Hai (Geng et al, 2011), Guang Zhou (Situ et al, 2013) and Xi'an and may further increase in importance considering the continuing 10 greening trend over China in the future.…”

Observationally constrained modelling of atmospheric oxidation capacity and photochemical reactivity in Shanghai, China

“…The sensitivity study of the WRF-Chem model quantified the threshold value of the emission ratio of NOx/VOCs for switching from a VOC-limited to a NOx-limited regime in Shanghai (Tie et al, 2013). Another study has estimated that future ozone will be reduced by 2-3 ppbv in suburban, and more than 4 ppbv in rural areas in Shanghai after 2020 (Xu et al, 2019). However, few of these earlier studies investigated atmospheric oxidation capacity and radical chemistry in Shanghai with an observation-constrained model.…”