APCG studies NO2 levels above Greece prior and during the Covid19 pandemic, retrieving Sentinel5P data. Significant decreases in the air pollution levels are seen, especially for Athens and Thessaloniki, the highest of which occur during March. Findings are consistent to previous reports (e.g. here, in Greek).
The relevant article is now published in Κόsμος, the official NOA magazine for research dissemination to the public. You can read the article here (in greek).