Evaluation of the impact of the COVID-19 pandemic on photochemical pollution in urban areas

Background: The effect of confinement due to the coronavirus disease 2019 (COVID-19) pandemic on air pollution has been investigated in several cities. Indeed, the concentration of the main air pollutants have decreased significantly due to the decline in activities consuming fossil fuels. However, it was found that the concentration of ozone (O3) has increased in Nice, Rome, Valence, Barcelona, Turin, and Wuhan. The main objective of this study was to assess the impact of the COVID-19 pandemic on photochemical pollution in Oran, Algeria. Methods: In Oran, a port city in the north-west of Algeria, the level of tropospheric ozone pollution was measured automatically every 15 min for 10 days at the same location before and after the confinement period, using an electronic nose, called APOMOS (air pollution monitoring system). This electronic circuit is equipped with an electrochemical sensor (MQ131) as well as a temperature and humidity sensor. Sampling was carried out in the central part of the Oran agglomeration from May to June 2020. The data related to the direction and intensity of the wind were processed to find a correlation between these parameters and the concentration of ozone in the studied area. Results: The impact of confinement on the increase of the ozone pollution levels in Oran, was estimated to be 52%. On the other hand, the statistical study of the pollution levels, the intensity and direction of the wind indicates that the important part of the downtown is involved in the generation of tropospheric ozone. Conclusion: The confinement due to the COVID-19 pandemic in Oran led to the reduction of the road traffic and pollutants emissions and the increase of ozone levels in urban area. Thus, ozone was less degraded because there were low levels of nitrogen oxides (NOx) in the atmosphere of this city during the confinement period.