Preprints
https://doi.org/10.5194/acp-2021-579
https://doi.org/10.5194/acp-2021-579

  30 Aug 2021

30 Aug 2021

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

Impact of the COVID-19 pandemic on the observed vertical distributions of PM2.5, NOx, and O3 from a tower in the Pearl River Delta

Lei Li1,2,3, Chao Lu4, Pak-Wai Chan5, Zi-Juan Lan6, Wen-Hai Zhang7, Hong-Long Yang4, and Hai-Chao Wang1,2,3 Lei Li et al.
  • 1School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, 519082, PR China
  • 2Guangdong Provincial Observation and Research Station for Climate Environment and Air Quality Change in the Pearl River Estuary, Zhuhai, 519082, China
  • 3Key Laboratory of Tropical Atmosphere-Ocean System (Sun Yat-sen University), Ministry of Education, Zhuhai, 519082, China
  • 4Shenzhen National Climate Observatory, Meteorological Bureau of Shenzhen Municipality, Shenzhen, 518040, PR China
  • 5Hong Kong Observatory, 999077, Hong Kong
  • 6Shenzhen Research Academy of Environmental Sciences, Shenzhen, 518001, PR China
  • 7Shenzhen Academy of Severe Storms Science, Shenzhen, 518057, PR China

Abstract. The outbreak of the 2019 novel coronavirus (COVID-19) has brought tremendous impact and influence on human health and social economy around the world. The lockdown implemented in China, starting on 23 January 2020, led to large reductions in human activities and the associated emissions. Sharp declines in primary pollution provided a unique chance to examine the relationships between anthropogenic emissions and air quality. Here, we report measurements of air pollutants and meteorological parameters at different heights on a tall tower in the Pearl River Delta, China, to investigate the response of the vertical scales of pollutants to reductions in human activities. Compared to the pre-lockdown period (starting from 16 December 2019), the observations showed that surface layer NOx, PM2.5 and mean values of the daily maximum 8 h average O3 (MDA8O3) had significant reductions of 76.8 %, 49.4 %, and 18.6 % respectively, but the average O3 increased (9.7 %) during lockdown period. The vertical profiles of NOx and O3 changed during the lockdown period, but not those of PM2.5. The correlation between PM2.5 and O3 was statistically significant, but not that between PM2.5 and NOx for data collected at four different heights during the lockdown period. The significance of these correlations was the opposite during the pre-lockdown period, indicating that the main composition of PM2.5 has changed dramatically since the lockdown, which is transited from primary aerosol dominating or nitrate dominating (affected by NOx) before lockdown to secondary organic aerosol dominant dominating (affected by O3) during the lockdown. We find weaker diurnal variation of O3 during the lockdown period is similar to the case at background regions. O3 concentrations were not sensitive to NOx concentrations during lockdown, which implies that O3 levels during the lockdown are more representative of the regional background, for which anthropogenic emissions are low and photochemical formation is not a significant ozone source. This evidence suggests that significant reductions of anthropogenic emissions are effective in simultaneous mitigation of PM2.5 and O3 levels.

Lei Li et al.

Status: open (until 11 Oct 2021)

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

Lei Li et al.

Lei Li et al.

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Short summary
The COVID-19 induced lockdown provided a time-window to study the impact of emission decrease on atmospheric environment. A 350 m meteorological tower in the Pearl River Delta recorded the vertical distribution of pollutants during the lockdown period. The observation confirmed that an extreme emission reduction, can reduce the concentrations of fine particles and the peak concentration of ozone at the same time, which had been taken as difficult to realize in the past in many regions.
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