The Impact of COVID-19 Confinement Measures on the Air Quality in an Urban-Industrial Area of Portugal

Abstract

This study evaluated the temporal variability of the concentrations of pollutants (namely, NO2, O3, PM2.5, PM10 and SO2) in an urban-industrial area of mainland Portugal during two decades (from 2001 to 2020), to assess the impact of the COVID-19 pandemic on the levels of these atmospheric pollutants. Mean levels of pollutants in 2020 were compared with those measured in the six previous years (2014–2019). A significant improvement in air quality, namely regarding PM10 and NO2, was found and it can be attributable to the restrictions of anthropogenic activities (such as traffic) promoted during the March–May 2020 national lockdown that occurred due to the pandemic. Significant and expressive reductions of 44.0% and 40.3% were found in April 2020 for NO2 and PM10, respectively, showing the impact of local traffic in the study area. A similar trend of reduction for these pollutants was also found in the following months. However, ozone levels did not show the same trend, with significant increases in several months after the lockdown period, highlighting other contributions to this pollutant. This unique period can be considered as a living lab, where the implementation of strict measures due to COVID-19 confinement promoted the reduction of anthropogenic activities and allowed us to understand more comprehensively their impact on local air quality.

Source apportionment of PM2.5 before and after COVID-19 lockdown in an urban-industrial area of the Lisbon metropolitan area, Portugal

“…The same trend was observed for NO 3 − , for which the most pronounced reduction (76.4%) was observed, from the winter/pre-confinement (2690 ± 3030 ng.m −3 ) to the post-confinement period (635 ± 575 ng.m −3 , p -value = 0.000), with no significant difference between the two post-confinement campaigns (p-value >0.050). This is in line with the concentrations of its gaseous precursor NO 2 in the studied area, which registered significant reductions in the pandemic period of 2020 relative to the previous six-year averages (44.0% in April, 17.4% in May, 29.0% in June and 31.6% in August) ( Gamelas et al, 2021 ). Less pronounced reductions in NO 3 − concentrations were generally observed worldwide (namely 17.6%, in Lanzhou ( Chang et al, 2022 ) and 6.7%, in Linfen ( Liu et al, 2022 )), but there were also cases in which an increase was observed, as the result of enhanced atmospheric oxidation capacity ( Ma et al, 2022 ).…”

“…For this reason, a comparison with the previous years should be performed. In fact, the mean PM 10 concentrations registered in Paio Pires monitoring station in the previous six years (2014-2019) had a significantly higher value of 27 ± 15 μg.m −3 ( Gamelas et al, 2021 ) when compared with the PM 10 mean concentrations found for the 128 sampling days in the present study (24 ± 14 μg.m −3 , p -value = 0.042), thus confirming the impact of the confinement measures on PM levels.…”

“…In a previous study ( Gamelas et al, 2021 ), where the temporal variability of the concentrations of air pollutants (NO 2 , O 3 , PM 2.5 , PM 10 and SO 2 ) was assessed in Seixal, with an emphasis on the last six years, a significant improvement in air quality regarding PM 10 and NO 2 was found due to the COVID-19 lockdown, but O 3 and SO 2 levels did not follow that trend, especially in summer.…”

“…In Seixal, a highly populated urban-industrial area in the Lisbon Metropolitan Area, comprising heavy industry such as steelworks, and crossed by highways with high density commuting traffic, has suffered from poor air quality in the last decades ( Gamelas et al, 2021 ). Occasional settled dust events, when houses, cars, plants etc.…”

Spatial Distribution of Air Pollution, Hotspots and Sources in an Urban-Industrial Area in the Lisbon Metropolitan Area, Portugal—A Biomonitoring Approach

“…In the present study area, a drastic decrease of concentrations of PM 10 and NO 2 was registered in April 2020 (−40.3% and −44.0%, respectively), compared to the previous six years (a significant difference, with p-value = 0.000) [52]. In May 2020, a lower but still significant decrease of PM 10 (−16.7%, p-value = 0.000) and NO 2 (−17.4%, p-value = 0.048) was also registered.…”