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...

Abstract. PM1 (particulate matter with an aerodynamic diameter <1 μm) non-refractory components and black carbon were measured continuously together with additional air quality and atmospheric parameters at an urban background site in Barcelona, Spain, during March 2009 (campaign DAURE, Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean). Positive matrix factorization (PMF) was conducted on the organic aerosol (OA) data matrix measured by an aerosol mass spectrometer, on both unit mass (UMR) and high resolution (HR) data. Five factors or sources could be identified: LV-OOA (low-volatility oxygenated OA), related to regional, aged secondary OA; SV-OOA (semi-volatile oxygenated OA), a fresher oxygenated OA; HOA (hydrocarbon-like OA, related to traffic emissions); BBOA (biomass burning OA) from domestic heating or agricultural biomass burning activities; and COA (cooking OA). LV-OOA contributed 28% to OA, SV-OOA 27%, COA 17%, HOA 16%, and BBOA 11%. The COA HR spectrum contained substantial signal from oxygenated ions (O:C: 0.21) whereas the HR HOA spectrum had almost exclusively contributions from chemically reduced ions (O:C: 0.03). If we assume that the carbon in HOA is fossil while that in COA and BBOA is modern, primary OA in Barcelona contains a surprisingly high fraction (59%) of non-fossil carbon. This paper presents a method for estimating cooking organic aerosol in ambient datasets based on the fractions of organic mass fragments at m/z 55 and 57: their data points fall into a V-shape in a scatter plot, with strongly influenced HOA data aligned to the right arm and strongly influenced COA data points aligned to the left arm. HR data show that this differentiation is mainly driven by the oxygen-containing ions C3H3O+ and C3H5O+, even though their contributions to m/z 55 and 57 are low compared to the reduced ions C4H7+ and C4H9+. A simple estimation method based on the markers m/z 55, 57, and 44 is developed here and allows for a first-order-estimation of COA in urban air. This study emphasizes the importance of cooking activities for ambient air quality and confirms the importance of chemical composition measurements with a high mass and time resolution.

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