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+NO 2 ) 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. • Form 2001 to 2021, O 3 concentrations increase by 0.3 ppb·yr -1 , while other pollutants experience varying degrees of decline. • During the COVID-19, NOx concentrations fall to 30% of the original levels, while O 3 concentrations increase exponentially. • Urban London O 3 pollution is in the VOC-limited regime. • The surge of O 3 concentrations during the COVID-19 is because NOx declined rapidly.