we attempted to evaluate the changes in levels of some air pollutants (mainly PM10, NO2and SO2) in Salé city (North-Western Morocco) during the lockdown measures. In this context, a continuous measurement of PM10, SO2and NO2was 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 PM10, SO2and NO2. PM10levels were much less reduced than NO2. The three-dimensional air mass backward trajectories, using the HYSPLIT model, demonstrated the benefits of PM10local 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.
The reduction in PM10, SO2 and NO2 concentrations, in the studied area, can mainly be attributed to the drastic measures limiting human movement and industrial activities during the Covid-19 pandemic, which resulted in a significant reduction in emissions from vehicle exhaust and industrial production. The authors believe that the PM10, NO2 and SO2 concentrations will continue to decrease and keep down to minimal levels during the Covid-19 lockdown period.
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