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To control the spread of COVID-19, in March 2020 exceptional restrictive measures were taken imposing a radical change in the lifestyle of millions of citizens around the world, albeit for a short period of time. The national lockdown, which in Italy lasted from 10 March to 18 May 2020, was a unique opportunity to observe the variation in air quality in urban environments in a condition of almost total traffic block and a strong reduction in work activities. In this paper, the data from seventeen urban monitoring sites in Tuscany are presented by comparing PM and NO2 of the two months before the start of the lockdown and the two after with the corresponding months of the previous three years. The results show that the total load of PM2.5 and PM10 decreased but it did not exhibit significant changes compared to previous years, while NO2 undergoes a drastic reduction. For three of these sites, the chemical composition of the collected samples was measured by thermo-optical, ion chromatography and PIXE analysis, and the application of multivariate PMF analysis allowed the PM10 source identification and apportionment. Thanks to these analyses it was possible to explain the low sensitiveness of PM10 to the lockdown effects as due to different, sometimes opposite, behaviors of the different sources that contribute to PM. The results clearly indicated a decline in pollution levels related to urban traffic and an increase in the concentration of sulfate for all sites during the lockdown period. [ABSTRACT FROM AUTHOR]

Elemental composition of the fine (PM2.5) and coarse (PM2.5-10) fraction of atmospheric particulate matter was measured at hourly time resolution by the use of a "streaker" sampler during a winter period at a Central European urban background site in Warsaw, Poland. A combination of multivariate (Positive Matrix Factorization), wind- (Conditional Probability Function) and trajectory-based (Cluster Analysis) receptor models, was applied for source apportionment. It allowed for identification of 5 similar sources in both fractions, including sulfates, soil dust, road salt, traffic- and industry-related sources. Another 2 sources, i.e., Cl-rich and wood and waste combustion, were identified in the fine fraction solely. In the fine fraction, aged sulfate aerosol related with emissions from solid fuel combustion in the residential sector located outside the city was the largest contributing source to fine elemental mass (44 %), while traffic-related sources, including soil dust mixed with road dust, road dust, as well as exhaust and non-exhaust traffic emissions, had the biggest contribution in the coarse elemental mass (together accounting for 83 %). Regional transport of aged aerosols and more local impact of the rest of identified sources played a crucial role in aerosol formation over the city. In addition, 2 intensive Saharan dust outbreaks were registered on 18th February and 8th March 2016. Both episodes were characterized by long-range transport of dust at 1 500 m and 3 000 m over Warsaw, as well as the concentrations of the soil component being 7 (up to 3.5 µg m−3) and 6 (up to 6.1 µg m−3) times higher than the mean concentrations observed during non-episodes days (0.5 µg m−3 and 1.1 µg m−3) in the fine and coarse fraction, respectively. The set of receptor models applied to the high time resolution data allowed to follow in detail the daily evolution of the aerosol elemental composition and to identify distinct sources contributing to the concentrations of different PM fractions, as well as revealed "multi-faces" of some elements, having diverse origin in the fine and coarse fraction. The hourly resolution of meteorological conditions and air mass back trajectories empower to follow transport pathways of the aerosol as well. [ABSTRACT FROM AUTHOR]

In this paper, a new methodology coupling aerosol optical and chemical parameters in the same source apportionment study is reported. This approach gives additional relevant information such as estimates for the atmospheric Ångström Absorption Exponent (α) of the sources and Mass Absorption Coefficient (MAC) for fossil fuel emissions at different wavelengths. A multi-time source apportionment study using Multilinear Engine ME-2 was performed on a PM10 dataset with different time resolution (24 hours, 12 hours, and 1 hour) collected during two different seasons in Milan (Italy) in 2016. Samples were optically analysed to retrieve the aerosol absorption coefficient bap (in Mm−1) at four wavelengths (λ = 405 nm, 532 nm, 635 nm and 780 nm) and chemically characterised for elements, ions, levoglucosan, and carbonaceous components. Time-resolved chemically speciated data were coupled with bap multi-wavelength measurements and introduced as input data in the multi-time receptor model; this approach was proven to strengthen the identification of sources being particularly useful when important chemical markers (e.g. levoglucosan, elemental carbon, ...) are not available. The final solution consisted in 8 factors (nitrate, sulphate, resuspended dust, biomass burning, construction works, traffic, industry, aged sea salt); the implemented constraints led to a better physical description of factors and the bootstrap analysis supported the goodness of the solution. As for bap apportionment, consistently to what expected, the two factors assigned to biomass burning and traffic were the main contributors to aerosol absorption in atmosphere. A relevant feature of the approach proposed in this work is the possibility of retrieving many other information about optical parameters; for example, opposite to the more traditional approach used by optical source apportionment models, here we obtained the atmospheric Ångström Absorption Exponent (α) of the sources (α biomass burning = 1.83 and α fossil fuels = 0.80), without any a priori assumption. In addition, an estimate for the Mass Absorption Cross section (MAC) for fossil fuel emissions at four wavelengths was obtained and found to be consistent with literature ranges. [ABSTRACT FROM AUTHOR]

Natural sources' contribution to ambient air particulate matter (PM) concentrations is often not considered; however, it may be significant for certain areas and during specific periods of the year. In the framework of the AIRUSE-LIFE+ project, state-of-the-art methods have been employed for assessing the contribution of major natural sources (African dust, sea salt and forest fires) to PM concentrations, in Southern European urban areas. 24 h measurements of PM10 and PM2.5 mass and chemical composition were performed over the course of a year in five cities: Porto, Barcelona, Milan, Florence and Athens. Net African dust and sea salt concentrations were calculated based on the methodologies proposed by EC (SEC 2011/208). The contribution of uncontrolled forest fires was calculated through receptor modelling. Sensitivity analysis with respect to the calculation of African dust was also performed, in order to identify major parameters affecting the estimated net dust concentrations. African dust contribution to PM concentrations was more pronounced in Eastern Mediterranean, with the mean annual relative contribution to PM10 decreasing from 21% in Athens, to 5% in Florence, and around 2% in Milan, Barcelona and Porto. The respective contribution to PM2.5 was calculated equal to 14% in Athens and from 1.3 to 2.4% in all other cities. High seasonal variability of contributions was observed, with dust transport events occurring at different periods in the Western and Eastern Mediterranean basin. Sea salt was mostly related to the coarse mode and also exhibited significant seasonal variability. Sea salt concentrations were highest in Porto, with average relative contributions equal to 12.3% for PM10. Contributions from uncontrolled forest fires were quantified only for Porto and were low on an annual basis (1.4% and 1.9% to PM10 and PM2.5, respectively); nevertheless, contributions were greatly increased during events, reaching 20 and 22% of 24 h PM10 and PM2.5 concentrations, respectively. [ABSTRACT FROM AUTHOR]

The third intensive measurement period (IMP) organised by the European Monitoring and Evaluation Programme (EMEP) under the UNECE CLTRAP took place in summer 2012 and winter 2013, with PM10 filter samples concurrently collected at 20 (16 EMEP) regional background sites across Europe for subsequent analysis of their mineral dust content. All samples were analysed by the same or a comparable methodology. Higher PM10 mineral dust loadings were observed at most sites in summer (0.5-10 µg m-3) compared to winter (0.2-2 µg m-3), with the most elevated concentrations in the southern- and easternmost countries, accounting for 20-40% of PM10. Saharan dust outbreaks were responsible for the high summer dust loadings at western and central European sites, whereas regional or local sources explained the elevated concentrations observed at eastern sites. The eastern Mediterranean sites experienced elevated levels due to African dust outbreaks during both summer and winter. The mineral dust composition varied more in winter than in summer, with a higher relative contribution of anthropogenic dust during the former period. A relatively high contribution of K from non-mineral and non-seasalt sources, such as biomass burning, was evident in winter at some of the central and eastern European sites. The spatial distribution of some components and metals reveals the influence of specific anthropogenic sources on a regional scale: shipping emissions (V, Ni, and SO42-) in the Mediterranean region, metallurgy (Cr, Ni, and Mn) in Central and Eastern Europe, coal combustion (As, Se, and SO42-) in Eastern countries, and traffic (Cu) at sites affected by emissions from nearby cities. [ABSTRACT FROM AUTHOR]