Impact of Covid-19 lockdown on PM_(10), SO_2 and NO_2 concentrations in Sale City (Morocco)

摘要

Covid-19 was first reported in Morocco on March 2,2020. Since then, to prevent its propagation, the Moroccan government declared a state of health emergency. A set of rapid and strict countermeasures have taken, including locking down cities, limiting population's mobility and prohibiting almost all avoidable activities. In the present study, we attempted to evaluate the changes in levels of some air pollutants (mainly PM_(10), NO_2 and SO_2) in Sale city (North-West-ern Morocco) during the lockdown measures. In this context, a continuous measurement of PM_(10), SO_2 and NO_2 was carried before and during the Covid-19 lockdown period. As a consequence of the security measures and control actions undertaken, the emissions from vehicle exhaust and industrial production were significantly reduced, which contribute to the decrease in the concentrations of the studied pollutants. The obtained results showed that the difference between the concentrations recorded before and during the lockdown period were respectively 75%, 49% and 96% for PM_(10), SO_2 and NO_2. PM_(10) levels were much less reduced than NO_2. The three-dimensional air mass backward trajectories, using the HYSPLIT model, demonstrated the benefits of PM_(10) local emission reductions related to the lockdown were overwhelmed by the contribution of long-range transported aerosols outside areas. In addition, noteworthy differences in the air mass back trajectories and the meteorology between these two periods were evidenced.