Characteristic changes of ozone and its precursors in London during COVID-19 lockdown and the ozone surge reason analysis

The London COVID-19 lockdown reduced emissions from anthropogenic sources, providing unique conditions for air contamination research. This research uses tropospheric ozone (O-3), volatile organic compounds (VOCs) and NOx (NO+NO2) hourly monitoring data at the London Marylebone Road station from 2001 to 2020 to investigate the effects of lockdown on (O-3) and its precursors. Both NOx and VOCs pollution showed a decreasing trend between 2001 and 2021, with a gradual increase in O-3 in contrast. During the COVID-19 lockdown period (from 23rd March to July 4, 2020), there was a surge in O-3 concentration, accompanied by a sharp reduction in NOx concentrations. Because all the monitoring VOCs/NOx results were less than eight during the lockdown, indicating that O-3 formation in urban London was in the VOC-limited regime. The rapid increase in O-3 concentrations caused by the lockdown was closely related to the rapid decrease in NOx emissions.