The European Environment Agency’s (EEA) data confirm large decreases in air pollutant concentrations — of nitrogen dioxide (NO2) concentrations in particular — largely due to reduced traffic and other activities, especially in major cities under lockdown measures. Reductions of around half have been seen in some locations. The EEA’s data are measured hourly, on the ground, at about 3,000 monitoring stations across European countries. (Source: EEA)