The Impact of the Lockdown Caused by the COVID-19 Pandemic on the Fine Particulate Matter (PM(2.5)) Air Pollution: The Greek Paradigm

Introduction: Responding to the coronavirus pandemic, Greece implemented the largest quarantine in its history. No data exist regarding its impact on PM(2.5) pollution. We aimed to assess PM(2.5) levels before, during, and after lockdown (7 March 2020–16 May 2020) in Volos, one of Greece’s most polluted industrialized cities, and compare PM(2.5) levels with those obtained during the same period last year. Meteorological conditions were examined as confounders. Methods: The study period was discriminated into three phases (pre-lockdown: 7 March–9 March, lockdown: 10 March–4 May, and post-lockdown period: 5 May–16 May). A wireless sensors network was used to collect PM(2.5), temperature, relative humidity, rainfall, and wind speed data every 2 s. Results: The lockdown resulted in a significant drop of PM(2.5) by 37.4% in 2020, compared to 2019 levels. The mean daily concentrations of PM(2.5) exceeded the WHO’s guideline value for 24-h mean levels of PM(2.5) 35% of the study period. During the strictest lockdown (23 March to 4 May), the mean daily PM(2.5) levels exceeded the standard 41% of the time. The transition from the pre-lockdown period into lockdown or post-lockdown periods was associated with lower PM(2.5) concentrations. Conclusions: A reduction in the mean daily PM(2.5) concentration was found compared to 2019. Lockdown was not enough to avoid severe exceedances of air pollution in Volos.