Fig. 1: Evolution of gas pollutants in Beijing.
From: Stratospheric influences on surface ozone increase during the COVID-19 lockdown over northern China
The temporal variations in surface ozone (O3, red bar), carbon monoxide (CO, blue line) concentrations and relative humidity (RH, cyan line) from 11 to 20 February 2020 during the COVID-19 lockdown (CLD) period in Beijing. The average ozone (horizontal black solid line) and CO (horizontal black dashed line) concentrations during the CLD were used as baseline references. The period when the deep stratospheric intrusion occurred during 15–17 February was marked by the red arrow.
