Fig. 1.

The development of COVID-19 in Italy and the Veneto Region when the PM samples were collected. The graph was based on Gatto et al. (2020). Time marks (A, B, C, and D) represent the most critical epidemiological events and measures for both mobility and contact restrictions at each time point: A) On February 21, 2020 (day 1), “patient one” was officially confirmed as a case of COVID-19 by the “Ospedale Sacco” in Milan; by the end of the day, other 14 cases in Lombardy and 2 cases in Veneto were confirmed.

B) On February 23, 2020 (day 3), evidence for local transmission from “patient one” increased and new cases of infections was discovered in the municipality of Vo’ (Province of Padua). Ten municipalities in Lombardy and one in the Providence of Padua, identified as hotspots, were maintained under strict lockdown (i.e., labeled as critical red areas), while some preventive restrictions (e.g., temporary closure of schools and universities) were enforced in some regions.

C) On March 8, 2020 (day 17), the whole of Lombardy and 14 Italian provinces (including the Province of Padua) were set under lockdown by the application of the Prime Ministerial Decree (DPCM) of August 03, 2020. Social distancing measures were implemented in the whole country.

D) On March 10, 2020 (day 19), the lockdown area was extended to the whole nation by the application of the Prime Ministerial Decree (DPCM) of March 09, 2020; progressive restrictive limitations on mobility and social distance were also instituted.