• PM 10 , NO 2 and SO 2 concentrations were reduced by more than half during the covid-19 lockdown period. • Covid-19 countermeasures contribute to reduce all pollutant concentrations but with significant differences among them. • Long-range transported aerosols contributions overcame the PM 10 local emission reductions benefits related to the lockdown.
Implemented quarantine due to the ongoing novel coronavirus (agent of COVID-19) has an immense impact on human mobility and economic activities as well as on air quality. Since then, and due to the drastic reduction in pollution levels in cities across the world, a large discussion has been magnetized regarding if the lockdown is an adequate alternative counter-measure for enhancing air quality. This paper aimed at studying the Air Quality Index (AQI), PM2.5, and tropospheric NO2 levels in three lockdown phases (before, during, and after) among 21 cities around the world. Simple before/after comparison approach was carried out to capture the declining trend in air pollution levels caused by the lockdown restrictions. The results showed that the frequency distribution for NO2 is more variable than that for PM2.5, and the distribution is flatter from 2020 to the baseline 2018-2019 period. Besides, AQI, in most of the cities, has varied from high to mild pollution during the lockdown and was moderate before. Although during the lockdown, a reduction of 3 to 58% of daily NO2 concentrations was observed across the cities, an increase was detected in three cities including Abidjan (1%), Conakry (3%), and Chengdu (10%). Despite this mixed trend, the NO2 time series clearly showed the effect of the unlocking phase where the NO2 levels increased in almost all cities. Similarly, PM2.5 concentrations have increased in the post-lockdown period, with 50% of the cities reporting significant positive differences between the lock and the unlock phase. Then, the levels of PM2.5 were higher at the pre-lockdown phase than at any other time exhibiting a “U” shape. In addition, during Ramadan, it was noted that altered patterns of daily activities in some Islamic cities have a significant negative impact on air quality.
This study analyses the seasonal distribution in the superficial sediments of the Marchica watershed of trace and major elements, grain size, and total organic carbon. Samples were taken during the wet and dry seasons of 2018 in the mainstream valleys carrying the discharges to the Marchica Lagoon. Ecotoxicological indices (Enrichment Factor, Contamination Factor, Pollution-Load Index) and sedimen-quality guidelines were used to evaluate the ecotoxicological risk. The results revealed during both wet and dry seasons contamination by lead in all stream valleys. The northwest stream valley, characterized by some industrial activities, and the stream valley crossing the abandoned mine were the most polluted by zinc and copper. Minimal pollution for Cr, Co, and Ba was found during both the wet and dry seasons. Despite the restoration actions achieved around the Ramsar site of Marchica lagoon during the last decades, the watershed continues to have a negative impact on this ecosystem. Therefore, an environmental management strategy isnecessary, taking into account the rehabilitation of the abandoned mining sites, the rational use of pesticides and fertilizers in agriculture, and the environmental responsibility of industrial companies, especially those installed before the implementation of the national law on environmental impact studies.
The seasonal and spatial variations of particulate matter (PM2.5-10 and PM2.5) and its chemical composition have been studied over a one-year period in Kenitra city (2007-2008). The samples were collected using Gent stacked filters and dichotomous samplers in two size fractions: below 2.5 μm (fine) and 2.5 to 10 μm (coarse). The chemical compositions of the collected filters were evaluated by using Total X-ray Fluorescence and Atomic Absorption Spectroscopy. The influence of atmospheric transport scenarios on the levels of PM was elaborated by means of air mass back-trajectories, using the HYSPLIT™ model. This study allowed identifying four main transport patterns: short local flows over the Kenitra region, Northwesterly flows over the Atlantic Ocean, Northerly flows, and Southern flows. The highest PM2.5-10 concentrations were observed in the summer and the lowest in the winter. However, no significant seasonal variations were discerned for PM2.5 particles. The enrichment factor and risk assessment code were calculated to distinguish between anthropogenic influences and the natural background levels and assess the environmental risks of metals in PM2.5-10 and PM2.5 particles. A comparison of PM and metal concentrations in Kenitra city and other African cities (reported in the literature) revealed that that the values obtained in Kenitra city are significantly higher than those recorded for the other African cities (that are the subject of the comparison).
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