Response of surface ozone concentration to emission reduction and meteorology during the COVID-19 lockdown in Europe

For three-quarters of over 1,100 available monitoring stations, the average nitrogen dioxide (NO2) concentrations decreased by at least 2.7 μg·m−3 (or 25%) compared with the average concentrations recorded during the same period of the previous seven years. This reduction was not specific to urban or rural areas because the relative reduction was of similar magnitude in both areas.

The ozone (O3) response differed spatially, with positive anomalies in Northern Europe and negative anomalies in Southwestern Europe. Reduced cloudiness and related enhanced radiation in Northern Europe played a significant role in the increase of surface O3 concentrations by shifting the photochemical partitioning between NO2 and O3 toward more O3. The level of total oxidant (Ox = O3 + NO2) remained unchanged, except in Southwestern Europe where it decreased.