Preprints
https://doi.org/10.5194/acp-2021-866
https://doi.org/10.5194/acp-2021-866

  10 Jan 2022

10 Jan 2022

Review status: this preprint is currently under review for the journal ACP.

Measurement report: Variations in surface SO2 and NOx mixing ratios from 2004 to 2016 at a background site in the North China Plain

Xueli Liu1, Liang Ran2, Weili Lin1, Xiaobin Xu3, Zhiqiang Ma4, Fan Dong4, Di He4, Liyan Zhou4, Qingfeng Shi4, and Yao Wang4 Xueli Liu et al.
  • 1Key Laboratory of Ecology and Environment in Minority Areas (Minzu University of China), National Ethnic Affairs Commission, Beijing 100081, China
  • 2Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100089, China
  • 3Chinese Academy of Meteorological Sciences, Beijing, 100081, China
  • 4Beijing Shangdianzi Regional Atmosphere Watch Station, Beijing, 101507, China

Abstract. Strict air pollution control strategies have been implemented in recent decades in the North China Plain (NCP), previously one of the most polluted regions in the world, and have resulted in considerable changes in emissions of air pollutants. However, little is so far known about the long-term trends of the regional background level of NOx and SO2, along with the increase and decrease processes of regional emissions. In this study, the seasonal and diurnal variations of NOx and SO2 as well as their long-term trends at a regional background station in the NCP were characterized from 2004 to 2016. On average, SO2 and NOx mixing ratios were 5.7 ± 8.4 ppb and 14.2 ± 12.4 ppb, respectively. The seasonal variations in SO2 and NOx mixing ratios showed a similar pattern with a peak in winter and a valley in summer. However, the diurnal variations in SO2 and NOx mixing ratios greatly differed for all seasons, indicating different sources for SO2 and NOx. Overall, the annual mean SO2 exhibited a significant decreasing trend of ‒6.1 % yr−1 (R = −0.84, P < 0.01) from 2004 to 2016, which is very close to −6.3 % yr−1 of the annual SO2 emission in Beijing, and a greater decreasing trend of −7.4 % yr−1 (R = −0.95, P < 0.01) from 2008 to 2016. The annual mean of NOx showed a fluctuating rise of +3.4 % yr−1 (R = 0.38, P = 0.40) from 2005 to 2010, reaching the peak value (16.9 ppb) in 2010, and then exhibited an extremely significant fluctuating downward trend of −4.5 % yr−1 (R = 0.95, P < 0.01) from 2010 to 2016. After 2010, the annual mean NOx mixing ratios correlated significantly (R = 0.94, P < 0.01) with the annual NOx emission in North China. The decreasing rate (−4.8 % yr−1, R = −0.92, P < 0.01) of the annual mean NOx mixing ratios from 2011 to 2016 at SDZ are lower than the one (−8.8 % yr−1, R = −0.94, P < 0.01) for the annual NOx emission in the NCP and (−9.0 % yr−1, R = −0.96, P < 0.01) in Beijing. It indicated that surface NOx mixing ratios at SDZ had weaker influence than SO2 by the emission reduction in Beijing and its surrounding areas in the NCP. The increase in the amount of motor vehicles led to an increase in traffic emissions for NOx. This study supported conclusions from previous studies that the measures taken for controlling NOx and SO2 in the NCP in the past decades were generally successful. However, NOx emission control should be strengthened in the future.

Xueli Liu et al.

Status: open (until 21 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Xueli Liu et al.

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Short summary
Significant decreases in the annual mean NOx from 2011 to 2016 and SO2 from 2008 to 2016 affirm the effectiveness of relevant control measures on the reduction in NOx and SO2 emissions in the North China Plain (NCP). NOx at SDZ had weaker influence than SO2 by the emission reduction in Beijing and other areas in NCP. The increase in the amount of motor vehicles and the weak traffic restrictions have caused vehicle emissions on NOx that indicated that NOx emission control should be strengthened.
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