Characteristics and Trends of Ambient Ozone and Nitrogen Oxides at Urban, Suburban, and Rural Sites from 2011 to 2017 in Shenzhen, China

Abstract

The emissions of nitrogen oxides (NOx) decreased under China’s air quality control policies. However, concern remains regarding the response of ozone (O3) in the metropolitan areas. The characteristics and trends of ambient O3 and NOx in Shenzhen were investigated during the 2011–2017 period. Both the human population and vegetation are exposed to higher O3 at suburban and rural sites than at the urban site. The O3 weekend effect is significant (p = 0.062) at the urban site, with O3 levels 1.19 ppb higher on Sunday than on weekdays. Solar radiation, precipitation, and relative humidity are the most relevant meteorological factors that affect O3 daily variations. Wind speed is the least relevant factor, but wind direction is related to the presence of high O3 air concentrations. Both 1-h and 8-h O3 exhibit an increase, opposite to the trend of NOx. A slight decline in O3 occurs in autumn at less urbanized sites. The increase in O3 is more prevalent and rapid in the winter at more urbanized sites. This can be due to the transport of increased O3 from northern China, as well as a lowered O3 titration effect with NOx reduction. O3 increases fastest at the urban site, with an estimated rate of 4.3% (95% confidence intervals (CIs): 0.96, 8.25) per year (p < 0.05) for 8-h O3 and 2.5% (95% CIs: −0.46, 6.12) per year (p > 0.1) for 1-h O3, posing greater human health risks to areas with high population density.

Comparison of Ozone and PM2.5 Concentrations over Urban, Suburban, and Background Sites in China

“…9), with a higher correlation coefficient between background and suburban sites (R = 0.8). As for the regression fits, suburban values are closer to the background concentrations for O 3 , consistent with the findings in previous studies (Tong et al, 2017;Huang et al, 2018). We further calculate the Δ[MDA8] and Δ[PM 2.5 ] for summer (JJA) and winter (November-December, ND) between urban and background sites in 2017.…”

“…5c), likely because of regionally high emissions of both biogenic and anthropogenic VOCs (Liu et al, 2018) and the substantial NO x reductions (He et al, 2017;Song et al, 2017) transform a VOC-limited regime to a mixed sensitive environment over YRD (Jin and Holloway, 2015) and result in the increase in urban O 3 (Wang et al, 2019). In terms of interannual variation, Huang et al(2018) found that the urban [O 3 ] in Shenzhen, a city in PRD, increased faster than its nonurban counterpart during 2012-17, leading to a decline in the absolute Δ[MDA8]. A similar trend is also present in our analyses for the whole PRD domain during 2015-18 ( Fig.…”

“…In previous studies, the difference in air pollution between urban and nonurban areas has tended to be explored for a city (Han et al, 2013;Wang et al, 2015;Tong et al, 2017;Huang et al, 2018;Zheng et al, 2018;Zhao et al, 2019), several cities (Xue et al, 2014), or a certain region, such as the North China Plain (Xu et al, 2016), Yangtze River Delta (An et al, 2015), or Pearl River Delta (Zheng et al, 2010). However, the urban-to-suburban difference has not been compared among different regions.…”

Tougher Targets for China’s Clean Air Cities? Implications from Air Quality Assessment in Shenzhen

“…(www.preprints.org) | NOT PEER-REVIEWED | Posted: 5 October 2018 doi:10.20944/preprints201810.0101.v1NO2 concentrations which may be caused by its large pollution and its location adjacent to the SEZ districts. NO2 levels have been lowered over time, possibly linked to the traffic energy reform in Shenzhen and the national NOx regulation measures[14][15]31]. Meanwhile, O3 concentrations are increasing which are probably caused by lowered NOx titration effects in a VOC limited urban environment.…”

“…Meanwhile, O3 concentrations are increasing which are probably caused by lowered NOx titration effects in a VOC limited urban environment. Great challenges remain in controlling O3 in Shenzhen[31].The concentrations of all air pollutants in Shenzhen have met current national annual target values. The thresholds for PM and O3 of national air quality standard are inherited from WHO's interim target-1 (IT1).…”