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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Jul 2020

28 Jul 2020

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This preprint is currently under review for the journal ACP.

Measurement report: Long-term variations in carbon monoxide at a background station in China's Yangtze River Delta region

Yijing Chen1, Qianli Ma2, Weili Lin1, Xiaobin Xu3, Jie Yao2, and Wei Gao4 Yijing Chen et al.
  • 1College of Life and Environmental Sciences, Minzu University of China, Beijing 100081, China
  • 2Lin'an Atmosphere Background National Observation and Research Station, Lin'an 311307, Hangzhou, China
  • 3Key Laboratory for Atmospheric Chemistry, Chinese academy of meteorological sciences, Beijing 100081, China
  • 4Shanghai Key Laboratory of Meteorology and Health, Shanghai Meteorological Service, Shanghai 200030, China

Abstract. This study analyzed the long-term variations in carbon monoxide (CO) mixing ratios from January 2006 to December 2017 at the Lin'an regional atmospheric background station (LAN; 30.3° N, 119.73° E, 138 m a.s.l.) in China's Yangtze River Delta (YRD) region. The CO mixing ratios were at their highest (0.69 ± 0.08 ppm) and lowest (0.54 ± 0.06 ppm) in winter and summer, respectively. The average daily variation of CO exhibited a double-peaked pattern, with peaks in the morning and evening and a valley in the afternoon. A significant downward trend of −11.3 ppb/yr of CO was observed from 2006 to 2017 at the LAN station, which was in accordance with the negative trend of the average CO mixing ratios and total column retrieved from the satellite data (the Measurements Of Pollution In The Troposphere, MOPITT) over the YRD region during the same period. The average annual CO mixing ratio at the LAN station in 2017 was 0.51 ± 0.04 ppm, which was significantly lower than that (0.71 ± 0.12 ppm) in 2006. The decrease in CO levels was largest in autumn (−15.7 ppb/yr), followed by summer (−11.1 ppb/yr), spring (−10.8 ppb/yr), and winter (−9.7 ppb/yr). Moreover, the CO levels under relatively polluted conditions (the annually 95th percentiles) declined even more rapidly (−22.4 ppb/yr, α = 0.05, r = −0.68) from 2006 (0.91 ppm) to 2017 (0.58 ppm) and the CO levels under clean conditions (the annually 5th percentiles) were relatively stable throughout the years. The long-term decline and short-term variations in the CO mixing ratios at the LAN station were mainly attributed to the implementation of the anthropogenic pollution control measures in the YRD region and to the events like Shanghai Expo in 2020 and Hangzhou G20 in 2016. The decreased CO level may influence atmospheric chemistry over the region. The average OH reactivity of CO at the LAN station is estimated to significantly drop from 4.1 ± 0.7 s-1 in 2006 to 3.0 ± 0.3 s-1 in 2017.

Yijing Chen et al.

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Yijing Chen et al.

Yijing Chen et al.


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Short summary
CO is one of the major air pollutants. Our study showed that the long-term CO levels at a background station in one of the most developed areas of China decreased significantly and verified that this downward trend was attributed to the cut-down of anthropogenic emissions, which indicated that the adopted pollution control policies were effective. Also, this decrease has an implication for the atmospheric chemistry considering the negative correlation between CO levels and OH radical's lifetime.
CO is one of the major air pollutants. Our study showed that the long-term CO levels at a...