Changes in air quality during the lockdown in Barcelona (Spain) one month into the SARS-CoV-2 epidemic

Abstract

Journal Pre-proof J o u r n a l P r e -p r o o f Abstract Lockdown measures came into force in Spain from March 14th, two weeks after the start of the SARS-CoV-2 epidemic, to reduce the epidemic curve. Our study aims to describe changes in air pollution levels during the lockdown measures in the city of Barcelona (NE Spain), by studying the time evolution of atmospheric pollutants recorded at the urban background and traffic air quality monitoring stations. After two weeks of lockdown, urban air pollution markedly decreased but with substantial differences among pollutants. The most significant reduction was estimated for BC and NO2 (-45 to -51%), pollutants mainly related to traffic emissions. A lower reduction was observed for PM10 (-28 to -31.0%). By contrast, O 3 levels increased (+33 to +57% of the 8h daily maxima), probably due to lower titration of O 3 by NO and the decrease of NOx in a VOC-limited environment. Relevant differences in the meteorology of these two periods were also evidenced. The low reduction for PM10 is probably related to a significant regional contribution and the prevailing secondary origin of fine aerosols, but an in-depth evaluation has to be carried out to interpret this lower decrease. There is no defined trend for the low SO 2 levels, probably due to the preferential reduction in emissions from the least polluting ships. A reduction of most pollutants to minimal concentrations are expected for the forthcoming weeks because of the more restrictive actions implemented for a total lockdown, which entered into force on March 30 th . There are still open questions on why PM10 levels were much less reduced than BC and NO 2 and on what is the proportion of the abatement of pollution directly related to the lockdown, without meteorological interferences. Journal Pre-proof J o u r n a l P r e -p r o o f loads over the Barcelona Metropolitan Area (2000 km 2 with Barcelona city in the center, Figure 2) decreased during the lockdown by -57% compared with the reference period. The same comparison has been made for the same periods for 2019, and -22% was reduced in the second period, in this case, by meteorological effects. Journal Pre-proof J o u r n a l P r e -p r o o f DiscussionAs it could be expected, the lockdown, including restricted social contact, closing of restaurants, shops, and a large number of companies and administrative centers, temporarily reduced levels of specific air pollutants, mostly the primary dominated ones. The role of the meteorology is also evident and not quantified in this study. The most significant variation was observed for NO 2 . Urban NO 2 is emitted from combustion processes, mostly road traffic in urban areas, especially diesel and, to a lesser extent, gasoline, vehicles, industry, power generation, and shipping. Although the main source of PM10 in the urban background of Barcelona is road traffic (around 30 % of the annual mean) (Amato et al., 2016), other important sources are industrial sources, harbor emissions, construction works, dust resuspension, an...

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