The Positive Impact of the First-Wave COVID-19 Lockdown on Urban Air Quality in Greece

BACKGROUND AND AIM: Following the first confirmed cases of COVID-19 during the first wave of the pandemic, the Government of Greece imposed a nationwide lockdown on March 23rd 2019, one of the first in Europe. Our study assesses the impact of this lockdown on the air quality of Greece's two largest cities, Athens and Thessaloniki. METHODS: The average monthly concentrations of particulate matter (PM10 and PM2.5) and nitrogen oxides (NO and NO2) measured on a 24-hour basis were obtained from the Greek Ministry of the Environment and Energy. In order to assess the impact of the lockdown on air quality, data were divided into three periods: (a) pre-lockdown (1 September 2019 – 22 March 2020), (b) during lockdown (23 March 2020 – 3 May 2020), and (c) post-lockdown (4 May 2020 – 6 November 2020), which overlapped with the beginning of the second wave COVID-19. RESULTS:Nitrogen oxide showed the most striking decrease in Athens, ranging from 6 to 84% (during lockdown) and from 12 to 66% (post lockdown), respectively, and was most prominent at the urban traffic stations. Compared to the pre-lockdown period, Athens also experienced significant reductions in PM10 (13–38%), PM2.5 (1-40%) and NO2 (9–65%) concentrations. In Thessaloniki the most marked decrease was observed at the urban traffic stations for PM10 and PM2.5, where a 39% and 31% decrease was respectively observed when comparing the lockdown and post-lockdown periods. CONCLUSIONS:Our results indicate that there is a relationship between air pollution and lockdown measures. The time series of the 24-hour data for PM10, PM2.5, NO and NO2 concentrations showed a decrease during the six weeks of lockdown in both cities. The observed changes could be attributed to lower traffic volumes, working remotely and temporary suspension of industrial activities. KEYWORDS: air pollution, particulate matter, oxides of nitrogen