Preprints
https://doi.org/10.5194/acp-2021-227
https://doi.org/10.5194/acp-2021-227

  07 May 2021

07 May 2021

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

Measurement report: Long-term variations in surface NOx and SO2 from 2006 to 2016 at a background site in the Yangtze River Delta region, China

Qingqing Yin1, Qianli Ma2, Weili Lin1, Xiaobin Xu3, and Jie Yao2 Qingqing Yin 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

Abstract. China has been experiencing rapid changes in emissions of air pollutants in recent decades. Increased emissions of primary particulates and reactive gases caused severe haze in several polluted regions including the Yangtze River Delta (YRD). Measures implemented in recent years for improving air quality have reduced the emissions of NOX, SO2, etc. The emission changes of these gases are reflected by tropospheric columns from satellite observations and surface measurements of surface concentrations from urban sites. However, little is known about the long-term variations in regional background NOX and SO2. In this study, we present NOX and SO2 measurements from the Lin'an station (LAN, 119°44' E,30°18' N,138.6 m a.s.l.), one of the Global Atmosphere Watch (GAW) stations in China. We characterize the seasonal and diurnal variations and study the long-term trends of NOX and SO2 mixing ratios observed at LAN from 2006 to 2016. We also interpret the observed variations and trends in term of changes in meteorological conditions as well as emission of these gases. The overall average mixing ratios of NOX and SO2 during 2006–2016 were 13.6 ± 1.2 ppb and 7.0 ± 4.2 ppb, respectively. The averaged seasonal variations showed maximum values of NOx and SO2 in December (23.5 ± 4.4 ppb) and January (11.9 ± 6.2 ppb), respectively, and minimum values of 7.1 ± 0.8 ppb and 2.8 ± 2.3 ppb (both in July), respectively. The average diurnal variation characteristics of NOX and SO2 differed considerably from each other though the daily average mixing ratios of both gases were significantly correlated (R2 = 0.29, P < 0.001). The annual average mixing ratio of NOX increased during 2006–2011 and then decreased significantly at 0.78 ppb/yr (−5.16 %/yr, P < 0.01). The annual 95 % and 5 % percentiles of hourly NOX mixing ratios showed upward trends until 2012 and 2014, respectively, before a clear decline. The annual average mixing ratio of SO2 decreased significantly at 0.99 ppb/yr (−8.27 %/yr, P < 0.01) from 2006–2016. The annual 95 % and 5 % percentiles of hourly SO2 mixing ratios all exhibited significant (P < 0.001) downward trends at 3.18 ppb/yr and 0.19 ppb/yr, respectively. Changes in the total NOX and SO2 emissions as well as the industrial emissions in the YRD region were significantly correlated with the changes in annual NOX and SO2 mixing ratios. The significant decreases in NOX from 2011 to 2016 and SO2 from 2006 to 2016 highlight the effectiveness of relevant control measures on the reduction in NOX and SO2 emissions in the YRD region. A decrease of annual S / N ratio was found, suggesting a better efficacy in the emission reduction of SO2 than NOX. We found gradual changes in average diurnal patterns of NOX and SO2, which could be attributed to increasing contributions of vehicle emissions to NOX and weakening impacts of large sources on the SO2 concentration. This study reaffirms China's success in controlling both NOX and SO2 in the YRD but indicate at the same time a necessity to strengthen the NOX emission control.

Qingqing Yin et al.

Status: open (until 05 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment of Yin Q et al.: “Measurement report: Long-term variations in surface NOx and SO2 from 2006 to 2016 at a background site in the Yangtze River Delta region, China”', Anonymous Referee #1, 21 Jun 2021 reply

Qingqing Yin et al.

Qingqing Yin et al.

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Short summary
China has been experiencing rapid changes in emissions of air pollutants in recent decades. NOX and SO2 measurements from 2006 to 2016 at the Lin'an WMO GAW station were used to characterize the seasonal and diurnal variations and study the long-term trends. This study reaffirms China's success in controlling both NOX and SO2 in the YRD but indicate at the same time a necessity to strengthen the NOX emission control.
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