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Abstract Recently, there has been a flurry of publications assessing the effect of air pollution on neurodevelopment. Here we present a summary of the results obtained within the BRain dEvelopment and Air polluTion ultrafine particles in scHool childrEn (BREATHE) Project, which aimed to evaluate the effects of the exposure to traffic related air pollutants in schoolchildren in Barcelona. To this end, we comprehensively characterised air quality in 39 urban schools from Barcelona and identified the main determinants of children's increased exposure. We propose a series of measures to be implemented to improve air quality in schools within the urban context and, consequently, minimise the negative effects on children's neurodevelopment that we found to be associated with the exposure to air pollution. We also aimed to list some of the actions pushed by governments and the society (including school managers, parents, and children) that have been taking place around Europe for promoting better high quality in the school and its surroundings. Highlights • Air pollution was associated with decelerated cognitive development. • Traffic should be moved away from schools to improve air quality. • Safe school pathways can help promote active travel (e.g.: walk, bicycle). • Cleaning should be done after school hours to avoid exposure to ultrafine particles. [ABSTRACT FROM AUTHOR]

The current air quality situation in Europe is reviewed for the most critical pollutants, i.e.: PM10, PM2.5, N02, 03 and BaP. Reasons of incompliance, as well as major actions required for reaching further compliance of the WHO guidelines are discussed. For some pollutants there is a need for further scientific research in order to cost-efficiently abate urban and peri-urban pollution, especially for PMx and03. The policy and scientific challenges are identified for these five pollutants. These include, for policy, the need to solve the air quality problem caused by NOx-diesel-vehicle EU policy failure, the need to reduce PM and BaP emissions from an increasing domestic biomass burning combustion favoured by policy actions, the need to abate the currently high agricultural NH3 emissions, and devising specific and cost-effective 03 abatement strategies. Key scientific challenges include the need for an accurate source apportionment of secondary organic aerosols in urban areas, the abatement of vehicle wear and road dust resuspension, an accurate tropospheric 03 source apportionment identifying the hemispheric/regional/local contributions as well as the accurate modelling of 03 able to reproduce the complex meteorology favouring high 03 episodes around the Mediterranean, and yielding reliable sensitivity analysis for policy actions. Levels, origins and application of other non-regulated air quality parameters such as concentrations of ultrafine particles (UFP) and black carbon (BC) are discussed in view of their potential use in air quality standards. We conclude that monitoring of BC should provide accurate evaluations of the effectiveness of road traffic air quality measures and their associated health gains. In the case of UFP, although road traffic is the major contributing source to urban levels, in high insolation regions a significant fraction of urban UFP can be attributed to photochemical nucleation processes. Thus, caution is necessary when doing metaanalysis of health outcomes linked to urban UFP using data from diverse cities, where the finest aerosol fraction might be considerably different in both composition and origin. Finally a strategy to abate N02 and PM from road traffic in urban areas of Europe, based on 7 major pillars or action types, is presented. [ABSTRACT FROM AUTHOR]

Measurements of CO 2 and counting of occupants were carried out in 37 public bus trips during commuting rush hours in Barcelona (NE Spain) with the aim of evaluating parameters governing ventilation inside the vehicles and proposing actions to improve it. The results show that CO 2 concentrations (1039 and 934 ± 386 ppm, as average and median, during rush hours but with average reduced occupancy due to the fair to be infected by SARS-CoV-2 during the measurement period, and measured in the middle of the busses) are in the lower range of values recorded in the literature for public buses, however an improvement in ventilation is required in a significant proportion of the journeys. Thus, we found better ventilation in the older Euro 3+ (retrofitted with filter traps and selective catalytic reduction) and Euro 5 buses (average 918 ± 257 ppm) than in the hermetically closed new Euro 6 ones (1111 ± 432 ppm). The opening of the windows in the older buses yielded higher ventilation rates (778 ± 432 ppm). The opening of all doors at all stops increases the ventilation by causing a fall in concentrations of 200–350 ppm below inter-stop concentrations, with this effect typically lasting 40–50 s in the hermetically closed new Euro 6 hybrid buses. Based on these results a number of recommendations are offered in order to improve ventilation, including measurement of CO 2 and occupancy, and installation of ventilation fans on the top of the hermetically closed new buses, introducing outdoor air when a given concentration threshold is exceeded. In these cases, a CO 2 sensor installed in the outdoor air intake is also recommended to take into account external CO 2 contributions. • Measurements of CO 2 were carried out in public buses during commuting rush hours. • An evaluation of factors governing ventilation inside the vehicles was carried out, and actions to improve it were suggested. • The opening of the windows in the older buses yielded higher ventilation rates. • The opening of all doors at all stops increases the ventilation by causing a fall in concentrations lasting 40–50 s. • Measurement of CO 2 and occupancy and installation of roof ventilation fans in the hermetically closed new buses. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: An analysis of the hourly SO2 pollution patterns with time can be a useful tool for policy makers and stakeholders in developing more effective local policies in relation to air quality as it facilitates a deeper understanding of concentrations and potential source apportionment. A detailed analysis of hourly inter-annual, seasonal and weekday-specific SO2 concentration patterns using data obtained from 6 cities involved in the Aphekom project was conducted. This type of analysis has been done for other pollutants but less so for SO2, and not in a systematic fashion for a number of European cities. Methods: Individual diurnal SO2 profiles and working weekday versus weekend specific 24-hr plots were generated using hourly SO2 measurements from a roadside and an urban background monitoring sites for 1993, 2001 and 2009 for each of the 6 European cities (Athens, Barcelona, Brussels, London, Paris, and Vienna). This facilitated the assessment of city specific patterns and comparison of changes with time. Results: SO2 concentrations varied throughout the day and tended to be lower on the weekends. A general decreasing trend for SO2 levels with time was observable at all stations. Discussion & Conclusion: This study provides a useful European perspective on patterns of exposure. For the 6 EU cities examined, road traffic, heating, and shipping in port cities appeared to be important sources of SO2 emissions, and hence the driving components widely reflected in the diurnal profiles with lower levels on the weekend likely due to lower traffic volume and industry related emissions. Although ambient SO2 concentrations have fallen over the assessed study period at all measurement sites, the daily patterns remained relatively unchanged. [Copyright &y& Elsevier]

Abstract: Despite their burden in urban particulate air pollution, road traffic non-exhaust emissions are often uncontrolled and information about the effectiveness of mitigation measures on paved roads is still scarce. The present study is aimed to evaluate the effectiveness of mechanical sweeping/water flushing treatments in mitigating urban road dust resuspension and to quantify the real benefit in terms of ambient PM10 concentrations. To this aim a specific campaign was carried out in a heavily trafficked central road of Barcelona (Spain), a Mediterranean city suffering from a traffic-related pollution, both for a high car density and a frequent lack of precipitation. Several street washings were performed by means of mechanical sweepers and pressure water during night in all traffic lanes and sidewalks. PM10 levels were simultaneously compared with four reference urban background air quality stations to interpret any meteorological variability. At the downwind measurement site, PM10 concentrations registered a mean daily decrease of 8.8μgm−3 during the 24h after street washing treatments. However 3.7–4.9μgm−3 of such decrease were due to the meteorological variability detected at the upwind site, as well as at two of the reference sites. This reveals that an effective decrease of 4–5μgm−3 (7–10%) can be related to street washing efficiency. Mitigation of road dust resuspension was confirmed by investigating the chemical composition of airborne-PM10 filters. Concentrations of Cu, Sb, Fe and mineral matter decrease significantly with respect to concentrations of elemental carbon, used as tracer for exhaust diesel emissions. High efficiency of street washing in reducing road dust loads was found by performing periodic samplings both on the treated and the untreated areas. [Copyright &y& Elsevier]

This article synthesises the results obtained in several projects on atmospheric aerosol (particulate matter – PM) pollution developed during the last years in the Western Mediterranean. It focuses on particulate matter sources and the strategies for suitable monitoring in ambient air. The article has been structured in several sections that give response to the main questions that prompted these studies. After analysing the main PM features in the Mediterranean, a brief review of the main factors differentiating the particulate matter composition with respect to Central Europe is presented. Finally, the suitability of the different metrics or parameters for monitoring ambient air PM levels in different types of environments is discussed. [ABSTRACT FROM AUTHOR]

Abstract: A strong African dust outbreak episode affecting the Canary Islands from 28 to 31/07/02 has been characterised at the Izaña Observatory (IZO), located in the free troposphere (FT), and at Sta. Cruz de Tenerife (SCO), in the Marine Boundary Layer (MBL). The Saharan air mass intruded above the trade wind inversion layer resulting in daily mean PM levels of up to 616, 312, 98 and 26μgm−3 of TSP, PM10, PM2.5 and PM1, respectively, at IZO. As demonstrated by the vertical sounding profiles, the MBL is compressed during the Saharan intrusion, favouring the deposition of coarse dust particles to the MBL and giving rise to daily levels of up to 85, 52 and 30μgm−3 of PM10, PM2.5 and PM1, respectively, at SCO. A complete chemical and mineralogical characterisation has been performed for TSP and PM2.5 collected simultaneously at both sites. Levels of mineral elements increased during the Saharan episode at both sampling sites. In addition, at the MBL, the levels of the secondary inorganic aerosols registered during the Saharan episode were considerably higher than levels recorded during non-Saharan episodes. The partial formation of secondary coarse Ca and/or Na sulphates and nitrates by the reaction of gaseous pollutants (or derived oxidised phases), of a major local origin, with the natural aerosols has been deduced. These reactions may be favoured by the high concentration of coarse mineral and marine aerosols particles measured at SCO, the high relative humidity (RH) measured, as well as the strong compression of the MBL during the Saharan episode. [Copyright &y& Elsevier]

Time series (1996-2000) of levels of PM (PM10 and TSP) and gaseous pollutants recorded in air quality monitoring networks from Northeastern Spain were interpreted using meteorological data and satellite observations of African dust plumes. The main objective of this study was to identify the processes affecting time variations of PM levels on a day-to-day and seasonal basis. From March to October PM levels at rural, urban, and industrial sites vary as a function of the concatenation of Atlantic air mass advections (Atlantic episodes with Iow PM levels) and regional circulations (regional events with high PM levels, very often associated with high ozone levels), which favor the aging of air masses in the Western Mediterranean basin. During these regional episodes, PM is transported from urban/industrial to rural sites by meso-scale circulations. From November to February Iow PM levels are recorded at rural sites, and variations in PM levels at urban/industrial sites are governed by the successive occurrence of Atlantic episodes and local urban/industrial pollution events. The African dust outbreaks take place throughout the year and may induce PM levels to increase simultaneously in large areas of the Iberian peninsula. The difference between PM concentrations measured at urban and rural sites experiences a seasonal trend similar to that of levels of N0[sub x] and CO, which is characterized by a winter maximum due to the higher frequency of intensive local urban pollution events. However, maximum PM levels are recorded in summer at rural sites owing to the frequent occurrence of regional episodes. Furthermore, in three years of the study period (1997, 1998, and 2000), a secondorder PM maximum was also recorded at rural sites in March owing to intensive African dust outbreaks. [ABSTRACT FROM AUTHOR]

Many cities still exceed the European Union (EU) air quality limit values for particulate matter (PM 10 , particles with an aerodynamic diameter less than 10 μm) and/or nitrogen dioxide (NO 2 ). In an attempt to reduce emissions approximately 200 low emission zones (LEZs) have been established in 12 EU countries. These restrict the entry of vehicles based on the emission standard the vehicles were originally constructed to meet, but the restrictions vary considerably. This paper reviews the evidence on the efficacy of LEZs to improve urban air quality in five EU countries (Denmark, Germany, Netherlands, Italy and UK), and concludes that there have been mixed results. There is some evidence from ambient measurements that LEZs in Germany, which restrict passenger cars as well as heavy duty vehicles (HDVs), have reduced long term average PM 10 and NO 2 concentrations by a few percent. Elsewhere, where restrictions are limited to HDVs, the picture is much less clear. This may be due to the large number of confounding factors. On the other hand there is some, albeit limited, evidence that LEZs may result in larger reductions in concentrations of carbonaceous particles, due to traffic making a larger contribution to ambient concentrations of these particles than to PM 10 and PM 2.5 . The effects of day to day variations in meteorology on concentrations often mask more subtle effects of a LEZ. In addition, separating the direct effects of a LEZ from the effects of other policy measures, the economy and the normal renewal of the vehicle fleet is not easy, and may give rise to false results. [ABSTRACT FROM AUTHOR]

Most particles breathed on rail subway platforms are highly ferruginous (FePM) and extremely small (nanometric to a few microns in size). High magnification observations of particle texture and chemistry on airborne PM 10 samples collected from the Barcelona Metro, combined with published experimental work on particle generation by frictional sliding, allow us to propose a general model to explain the origin of most subway FePM. Particle generation occurs by mechanical wear at the brake–wheel and wheel–rail interfaces, where magnetic metallic flakes and splinters are released and undergo progressive atmospheric oxidation from metallic iron to magnetite and maghemite. Flakes of magnetite typically comprise mottled mosaics of octahedral nanocrystals (10–20 nm) that become pseudomorphed by maghemite. Continued oxidation results in extensive alteration of the magnetic nanostructure to more rounded aggregates of non-magnetic hematite nanocrystals, with magnetic precursors (including iron metal) still preserved in some particle cores. Particles derived from steel wheel and rails contain a characteristic trace element chemistry, typically with Mn/Fe = 0.01. Flakes released from brakes are chemically very distinctive, depending on the pad composition, being always carbonaceous, commonly barium-rich, and texturally inhomogeneous, with trace elements present in nanominerals incorporated within the crystalline structure. In the studied subway lines of Barcelona at least there appears to be only a minimal aerosol contribution from high temperature processes such as sparking. To date there is no strong evidence that these chemically and texturally complex inhalable metallic materials are any more or less toxic than street-level urban particles, and as with outdoor air, the priority in subway air quality should be to reduce high mass concentrations of aerosol present in some stations. [ABSTRACT FROM AUTHOR]

[Display omitted] • A global observational analysis of air quality changes due to COVID-19 is presented. • NO 2 decreased with heterogeneous changes in O 3 and PM 2.5 showing complex signals. • Urban oxidant was driven by primary NO 2 and by regional inputs at background sites. • Meteorology, chemistry, emissions, climate and socioeconomics all affect air quality. • More ambitious regional regulation is needed to meet WHO air quality guidelines. This global study, which has been coordinated by the World Meteorological Organization Global Atmospheric Watch (WMO/GAW) programme, aims to understand the behaviour of key air pollutant species during the COVID-19 pandemic period of exceptionally low emissions across the globe. We investigated the effects of the differences in both emissions and regional and local meteorology in 2020 compared with the period 2015–2019. By adopting a globally consistent approach, this comprehensive observational analysis focuses on changes in air quality in and around cities across the globe for the following air pollutants PM 2.5 , PM 10 , PMC (coarse fraction of PM), NO 2 , SO 2 , NOx, CO, O 3 and the total gaseous oxidant (OX = NO 2 + O 3) during the pre-lockdown, partial lockdown, full lockdown and two relaxation periods spanning from January to September 2020. The analysis is based on in situ ground-based air quality observations at over 540 traffic, background and rural stations, from 63 cities and covering 25 countries over seven geographical regions of the world. Anomalies in the air pollutant concentrations (increases or decreases during 2020 periods compared to equivalent 2015–2019 periods) were calculated and the possible effects of meteorological conditions were analysed by computing anomalies from ERA5 reanalyses and local observations for these periods. We observed a positive correlation between the reductions in NO 2 and NOx concentrations and peoples' mobility for most cities. A correlation between PMC and mobility changes was also seen for some Asian and South American cities. A clear signal was not observed for other pollutants, suggesting that sources besides vehicular emissions also substantially contributed to the change in air quality. As a global and regional overview of the changes in ambient concentrations of key air quality species, we observed decreases of up to about 70% in mean NO 2 and between 30% and 40% in mean PM 2.5 concentrations over 2020 full lockdown compared to the same period in 2015–2019. However, PM 2.5 exhibited complex signals, even within the same region, with increases in some Spanish cities, attributed mainly to the long-range transport of African dust and/or biomass burning (corroborated with the analysis of NO 2 /CO ratio). Some Chinese cities showed similar increases in PM 2.5 during the lockdown periods, but in this case, it was likely due to secondary PM formation. Changes in O 3 concentrations were highly heterogeneous, with no overall change or small increases (as in the case of Europe), and positive anomalies of 25% and 30% in East Asia and South America, respectively, with Colombia showing the largest positive anomaly of ~70%. The SO 2 anomalies were negative for 2020 compared to 2015–2019 (between ~25 to 60%) for all regions. For CO, negative anomalies were observed for all regions with the largest decrease for South America of up to ~40%. The NO 2 /CO ratio indicated that specific sites (such as those in Spanish cities) were affected by biomass burning plumes, which outweighed the NO 2 decrease due to the general reduction in mobility (ratio of ~60%). Analysis of the total oxidant (OX = NO 2 + O 3) showed that primary NO 2 emissions at urban locations were greater than the O 3 production, whereas at background sites, OX was mostly driven by the regional contributions rather than local NO 2 and O 3 concentrations. The present study clearly highlights the importance of meteorology and episodic contributions (e.g., from dust, domestic, agricultural biomass burning and crop fertilizing) when analysing air quality in and around cities even during large emissions reductions. There is still the need to better understand how the chemical responses of secondary pollutants to emission change under complex meteorological conditions, along with climate change and socio-economic drivers may affect future air quality. The implications for regional and global policies are also significant, as our study clearly indicates that PM 2.5 concentrations would not likely meet the World Health Organization guidelines in many parts of the world, despite the drastic reductions in mobility. Consequently, revisions of air quality regulation (e.g., the Gothenburg Protocol) with more ambitious targets that are specific to the different regions of the world may well be required. [ABSTRACT FROM AUTHOR]

Abstract: The eastward transport of aerosols exported from mainland Asia strongly influences air quality in the Japanese archipelago. The bulk of the inhalable particulate matter (PM10) in these intrusions comprises either natural, desert-derived minerals (mostly supermicron silicates) or anthropogenic pollutants (mostly submicron sulphates), in various states of mixing. We analyse PM10 collected in Kumamoto, SW Japan, during three contrasting types of aerosol intrusions, the first being dominated by desert PM which became increasingly mixed with anthropogenic components as time progressed, the second being a relatively minor event mixing fine, distal desert PM with anthropogenic materials, and the third being dominated by anthropogenic pollutants. Whereas the chemistry of the natural mineral component is characterised by “crustal” elements (Si, Al, Fe, Mg, K, Li, P, Sc, V, Rb, Sr, Zr, Th, lanthanoids), the anthropogenic component is rich in secondary inorganic compounds and more toxic metallic elements (NH4 +, SO4 2−, As, Pb, Cd, Cu, Zn, Sn, Bi, Sb, and Ge). Some desert-dust (Kosa) intrusions are more calcareous than others, implicating geologically different source areas, and contain enhanced levels of NO3 −, probably as supermicron Ca(NO3)2 particles produced by chemical reaction between NOx pollutants (mostly from industry and traffic) and carbonate during atmospheric transport. The overall trace element chemistry of aerosol intrusions into Kumamoto shows low V/Rb, low NO3 −/SO4 2−, enhanced As levels, and unfractionated La/Ce values, which are all consistent with anthropogenic sources including coal emissions rather than those derived from the refining and combustion of oil fractionates. Geographically dispersed, residual sulphatic plumes of this nature mix with local traffic (revealed by OC and EC concentrations) and industrial emissions and dissipate only slowly, due to the dominance of submicron accumulation mode PM which is atmospherically persistent, and raise questions over the chronic health effects of breathing finely respirable sulphatic aerosol containing enhanced amounts of toxic metals. [Copyright &y& Elsevier]

Abstract: The geochemistry of PM10 filter samples collected at sea during the Scholar Ship Atlantic–Mediterranean 2008 research cruise reveals a constantly changing compositional mix of pollutants into the marine atmosphere. Source apportionment modelling using Positive Matrix Factorization identifies North African desert dust, sea spray, secondary inorganic aerosols, metalliferous carbon, and V–Ni-bearing combustion particles as the main PM10 factors/sources. The least contaminated samples show an upper continental crust composition (UCC)-normalised geochemistry influenced by seawater chemistry, with marked depletions in Rb, Th and the lighter lanthanoid elements, whereas the arrival of desert dust intrusions imposes a more upper crustal signature enriched in “geological” elements such as Si, Al, Ti, Rb, Li and Sc. Superimposed on these natural background aerosol loadings are anthropogenic metal aerosols (e.g. Cu, Zn, Pb, V, and Mn) which allow identification of pollution sources such as fossil fuel combustion, biomass burning, metalliferous industries, and urban–industrial ports. A particularly sensitive tracer is La/Ce, which rises in response to contamination from coastal FCC oil refineries. The Scholar Ship database allows us to recognise seaborne pollution sourced from NW Africa, the Cape Verde and Canary islands, and European cities and industrial complexes, plumes which in extreme cases can produce a downwind deterioration in marine air quality comparable to that seen in many cities, and can persist hundreds of kilometres from land. [Copyright &y& Elsevier]

In highly industrialized areas, abating particulate matter (PM) is complex owing to the variety of emission sources with different chemical profiles that may mix in the atmosphere. Gijón—an industrial city in northern Spain—was selected as a case study to better understand the key emission sources and improve air quality in highly industrialized areas. Accordingly, the trends of various air quality indicators (PM10, PM2.5, SO 2 , NO 2 , and O 3) during the past decade (2010–2019) were analyzed. Additionally, the inorganic and organic PM10 compositions were analyzed for source apportionment studies and to assess the impact of COVID-19 restrictions on PM10 levels. The results revealed that over the past decade, PM10 concentrations decreased, whereas PM2.5 concentrations dominated by secondary inorganic aerosols (SIA) remained relatively constant. Notably, during the COVID-19 lockdown, the PM10 concentration increased by 9.1%, primarily owing to an increase in regional SIA (>65%) due to specific meteorological conditions that favor the formation of secondary PM from gaseous precursors. Overall, eight key PM10 sources were identified: "industrial fugitive PM resuspension" (FPM, 28% of mean PM10 concentration), "aged sea spray" (SSp, 16%), "secondary nitrate" (SN, 15%), "local diffuse source" (LPM, 12%), "solid fuel combustion" (SFC, 7.8%), "biomass burning" (BB, 7.4%), "secondary sulphate" (SSu, 6.0%), and "sinter" (SIN, 4.5%). The PM10 concentration in Gijón is significantly influenced by the integrated steel industry (FPM, SFC, and SIN; 41% of PM10) and fugitive primary PM emissions were the main source (FPM and LPM; 40%). To reduce PM10 and PM2.5 concentrations, industrial fugitive emissions, which are currently poorly regulated, and SIA precursors must be abated. This study provides a methodological approach that combines trend analysis, chemical speciation, and source apportionment for assessing pollution abatement strategies in industrialized areas with a complex mix of emission sources. [Display omitted] • Complex industrial areas complicate PM source apportionment due to diverse emissions. • Concentrations decreased for PM10 but not for PM2.5 during last decade in Gijón. • Reducing secondary aerosol precursors is critical to abate PM2.5 levels. • Fugitive PM emissions from steelworks constitute a significant PM10 source. • Secondary PM formation may have caused an increase in PM during the COVID-19 lockdown. [ABSTRACT FROM AUTHOR]

The present study discloses the results of a comprehensive 3-years campaign (2010−2012) of air pollution measurements over an regional island background area (Can Llompart-Balearic Islands, Spain), contextualized with other measurements in the western Mediterranean region. Gaseous pollutants and particulate matter fractions were measured in real time; and PM 10 and PM 1 daily samples were obtained regularly from which chemical analyses were performed. Furthermore, during three intensive observation periods, real-time concentrations of particle number, black carbon and ammonia were additionally measured. Our results display particular diurnal and seasonal patterns for certain pollutants such as O 3 and particle number concentration. Our study reveals that concentrations of air pollutants and aerosol chemical composition are rather similar all over the central and western Mediterranean basin. The most abundant chemical components in PM 10 were mineral dust, followed by organic matter, sea spray and SO 4 2−; in PM 1 organic matter and SO 4 2− dominated, with significant contribution of mineral dust. Furthermore, a source apportionment Positive Matrix Factorization analysis was conducted. Natural sources exert most of the impact on the coarse-mode fraction, while most of fine-mode aerosols are linked to anthropogenic sources coming from local, regional or long range transport emissions. Prevalence of Atlantic air masses in 2010 had a positive effect in air quality, lowering mineral dust, SO 4 2− and EC concentrations. On the contrary, the high incidence of African dust and regional recirculation situations during the 2012 warm season favoured an overall PM load increase governed by mineral dust, SO 4 2− and trace elements associated to dust aerosols. The continuous increase in tourists in the Balearic Islands, and in general all around the Mediterranean, is clearly changing air quality patterns: while urban air pollution has strongly decreased since 2010, such downward trend is less pronounced at the regional scale, thus related to crescent sources such as maritime and air transport. Unlabelled Image • Air pollution and sources in the insular regional background of the WMED • Comparison with other sites in the region is presented. • Insular and pan-regional aerosol phenomenology is discussed and revised. • Local to regional sources are increasing, while long-range transport is decreasing. • Level of background air pollution remain due to boosted maritime and air transport. [ABSTRACT FROM AUTHOR]

This work studied the contribution of the geogenic sources volcanoes and fumaroles to the aerosol in marine atmosphere in the central Mediterranean basin. For this purpose, in the framework of the Med-Oceanor measurement program, we carried out a cruise campaign in the summer of 2017 to investigate the impact to the aerosol of the most important Mediterranean volcanoes (Mount Etna, Stromboli Island, and Marsili Seamount) and solfatara areas (Phlegraean Fields complex, Volcano Islands, Ischia Island, and Panarea submarine fumarole). We collected PM10 and PM2.5 samples in 12 sites and performed chemical characterization to gather information about the concentration of major and trace elements, elemental carbon (EC), organic carbon (OC), and ionic species. The use of triangular plots and the calculation of enrichment factors confirmed the interception of volcanic plume. We integrated the outcomes from chemical characterization with the use of factor analysis and SEM/EDX analysis for the source apportionment. Anthropogenic and natural sources including shipping emissions, volcanic and fumarolic load, as well as sea spray were identified as the main factors affecting aerosol levels in the study area. Furthermore, we performed pattern recognition analysis by stepwise linear discriminant analysis to seek differences in the composition of PM10 and PM2.5 samples according to their volcanic or solfatara origin. [ABSTRACT FROM AUTHOR]

The NO2 annual air quality limit value is systematically exceeded in many European cities. In this context, understanding human exposure, improving policy and planning, and providing forecasts requires the development of accurate air quality models at the urban (street level) scale. We describe CALIOPE-Urban, a system coupling CALIOPE – an operational mesoscale air quality forecast system based on the HERMES (emissions), WRF (meteorology) and CMAQ (chemistry) models – with the urban roadway dispersion model R-LINE. Our developments have focused on Barcelona city (Spain), but the methodology may be replicated for other cities in the future. WRF drives pollutant dispersion and CMAQ provides background concentrations to R-LINE. Key features of our system include the adaptation of R-LINE to street canyons, the use of a new methodology that considers upwind grid cells in CMAQ to avoid double counting traffic emissions, a new method to estimate local surface roughness within street canyons, and a vertical mixing parameterisation that considers urban geometry and atmospheric stability to calculate surface level background concentrations. We show that the latter is critical to correct the night-time overestimations in our system. Both CALIOPE and CALIOPE-Urban are evaluated using two sets of observations. The temporal variability is evaluated against measurements from five traffic sites and one urban background site for April–May 2013. While both systems show a fairly good agreement at the urban background site, CALIOPE-Urban shows a better agreement at traffic sites. The spatial variability is evaluated using 182 passive dosimeters that were distributed across Barcelona during 2 weeks for February–March 2017. In this case, the coupled system also shows a more realistic distribution than the mesoscale system, which systematically underpredicts NO2 close to traffic emission sources. Overall CALIOPE-Urban improves mesoscale model results, demonstrating that the combination of both scales provides a more realistic representation of NO2 spatio-temporal variability in Barcelona. [ABSTRACT FROM AUTHOR]

Vehicle interior air quality (VIAQ) was investigated inside 14 diesel/non-diesel taxi pairs operating simultaneously and under normal working conditions over six weekday hours (10.00–16.00) in the city of Barcelona, Spain. Parameters measured included PM 10 mass and inorganic chemistry, ultrafine particle number (N) and size, lung surface deposited area (LDSA), black carbon (BC), CO 2 , CO, and a range of volatile organic compounds (VOCs). Most taxi drivers elected to drive with windows open, thus keeping levels of CO 2 and internally-generated VOCs low but exposing them to high levels of traffic-related air pollutants entering from outside and confirming that air exchange rates are the dominant influence on VIAQ. Median values of N and LDSA (both sensitive markers of VIAQ fluctuations and likely health effects) were reduced to around 104 #/cm3 and < 20 µm2/cm3 respectively under closed conditions, but more than doubled with windows open and sometimes approached 105 #/cm3 and 240 µm2/cm3. In exceptional traffic conditions, transient pollution peaks caused by outside infiltration exceeded N = 106 #/cm3 and LDSA= 1000 µm2/cm3. Indications of self-pollution were implicated by higher BC and CO levels, and larger UFP sizes, measured inside diesel taxis as compared to their non-diesel pair, and the highest concentrations of CO (>2 ppm) were commonly associated with older, high-km diesel taxis. Median PM 10 concentrations (67 µg/m3) were treble those of urban background, mainly due to increased levels of organic and elemental carbon, with source apportionment calculations identifying the main pollutants as vehicle exhaust and non-exhaust particles. Enhancements in PM 10 concentrations of Cr, Cu, Sn, Sb, and a "High Field Strength Element" zircon-related group characterised by Zr, Hf, Nb, Y and U, are attributed mainly to the presence of brake-derived PM. Volatile organic compounds display a mixture which reflects the complexity of traffic-related organic carbon emissions infiltrating the taxi interior, with 2-methylbutane and n-pentane being the most abundant VOCs, followed by toluene, m-xylene, o-xylene, 1,2,4-trimethylbenzene, ethylbenzene, p-xylene, benzene, and 1,3,5-trimethylbenzene. Internally sourced VOCs included high monoterpene concentrations from an air freshener, and interior off-gassing may explain why the youngest taxi registered the highest content of alkanes and aromatic compounds. Carbon dioxide concentrations quickly climbed to undesirable levels (>2500 ppm) under closed ventilation conditions and could stay high for much of the working day. Taxi drivers face daily occupational exposure to traffic-related air pollutants and would benefit from a greater awareness of VIAQ issues, notably the use of ventilation, to encourage them to minimise possible health effects caused by their working environment. • Main PM 10 sources inside taxis are vehicle exhaust and non-exhaust (wear) particles. • PM 10 averaged 67 µg/m3 and enriched in Cr, Cu, Sn, Sb, Zr attributed to brake wear. • Self-pollution inside (especially older) diesel taxis raises BC, CO, and UFP size. • VOCs inside taxi dominated by 2-methylbutane, n-pentane and other exhaust emissions. • Intelligent use of taxi ventilation reduces infiltration and build-up of pollutants. [ABSTRACT FROM AUTHOR]

The NO2 annual air quality limit value is systematically exceeded in many European cities. In this context, understanding human exposure, improving policy and planning, and providing forecasts requires the development of accurate air quality models at urban (street-level) scale. We describe CALIOPE-Urban, a system coupling CALIOPE - an operational mesoscale air quality forecast system based on HERMES (emissions), WRF (meteorology) and CMAQ (chemistry) models - with the urban roadway dispersion model R-LINE. Our developments have focused on Barcelona city (Spain), but the methodology may be replicated for other cities in the future. WRF drives pollutant dispersion and CMAQ provides background concentrations to R-LINE. Key features of our system include the adaptation of R-LINE to street canyons, the use of a new methodology that considers upwind grid cells in CMAQ to avoid double counting traffic emissions, a new method to estimate local surface roughness within street canyons, and a vertical mixing parametrization that considers urban geometry and atmospheric stability to calculate surface level background concentrations. We show that the latter is critical to correct the nighttime overestimations in our system. Both CALIOPE and CALIOPE-Urban are evaluated using two sets of observations. The temporal variability is evaluated against measurements from five traffic sites and one urban background site for April-May 2013. While both systems show a fairly good agreement at the urban background site, CALIOPE-Urban shows a better agreement in traffic sites. The spatial variability is evaluated using 182 passive dosimeters that were distributed across Barcelona during two weeks for February-March 2017. In this case, also the coupled system shows a more realistic distribution than the mesoscale system, which systematically underpredicts NO2 close to traffic emission sources. Overall CALIOPE-Urban improves mesoscale model results, demonstrating that the combination of both scales provides a more realistic representation of NO2 spatio-temporal variability in Barcelona. [ABSTRACT FROM AUTHOR]

Underground subways transport large numbers of citizens in big cities, which must breathe air with limited ventilation. These atmospheric conditions may enhance the concentration of air pollutants from both outdoor and indoor air. The influence of ventilation conditions and maintenance activities on the concentrations of air pollutants have been studied. Particulate matter with aerodynamic diameter smaller than 2.5 μm (PM 2.5 ) in indoor air was sampled in ten platforms of nine subway stations of the metropolitan area of Barcelona in 2015 and 2016. These particles were analyzed for polycyclic aromatic hydrocarbons (PAH) and organic tracer compounds. The concentrations of PAH were in the range of the street air levels with higher PAH values in the colder period. No influence of nighttime maintenance activities was observed on the platform air quality during daytime. Source apportionment analysis using the concentrations of hopanes, nicotine and levoglucosan as molecular tracer compounds showed that 75% of the detected PAH at the platforms have an outdoor PM origin. The modern subway stations, with advanced ventilation and platform screen doors that separate the subway system from the platform, showed lowest PAH and PM concentrations. [ABSTRACT FROM AUTHOR]

Copper smelters represent a major anthropogenic source of SO 2 and sulphide-related elements into particulate matter, affecting the air quality of the surrounding areas. The implementation of measures to reduce the emission of gaseous contaminants and particles in industrial processes is a major issue, which aims to establish technological progress for cleaner production. In this sense, a long-range study covering the period 2001–2015 has been performed in the SW Spain, where one of the largest Cu-smelters in Europe is located. Trends of PM 10 and PM 2.5 levels and geochemical patterns were studied considering the following periods: prior (2001–2008), during (2009–2013) and after (2014–2015) the implementation of emission abatement technology (wet electrofilters, bag filters and lime injection) by this large industrial facility. The results evidenced relatively high concentrations of sulphide-related elements (annual mean of 6.1, 1.7, 0.7, 2.2, 2.0, 21.0 and 1.0 ng m −3 for As, Se, Cd, Sn, Sb, Pb and Bi, respectively) during 2001–2008. A reduction of 50% was observed for the last period (2.8, 0.5, 0.2, 1.6, 1.1, 6.7 an d 0.3 ng m −3 for the same elements, respectively) in PM 10 . A similar trend was observed for PM 2.5 samples. However, the number of episodes of SO 2 has not changed along the studied period (average 8 days/month), although the SO 2 concentration during the pollution episodes has markedly diminished from maximum peak concentrations of 350 μg m −3 to 170 μg m −3 . A high arsenic concentration is the main geochemical anomaly found in PM, reaching annual mean concentrations up to 10.4 ng m −3 in 2005 above the annual EU target value (6 ng m −3 ) in PM 10 , decreasing down to 2.7 and 2.9 ng m −3 in 2014 and 2015, respectively. However, sporadically high episodic levels are still recorded (e.g. 26.8 ng m −3 in 2014 and 14.9 ng m −3 in 2015). [ABSTRACT FROM AUTHOR]

As part of the European-funded IMPROVE LIFE project work programme experiments were performed in the Barcelona Metro system with the objective of better understanding the relationship between ventilation and air quality. The results demonstrate that tunnel ventilation plays an extremely important role in maintaining cleaner air and is capable of reducing both inhalable particulate matter (PM) mass and particle number concentration (> 0.3 μm) on platforms by over 50%, even in the presence of full-length platform screen doors. Another key influence on platform air quality is the chosen combination of fan power and forced air flow direction (impulsion of outdoor ambient air or extraction of subway indoor air): cleaner platform air was achieved using platform impulsion at higher power settings designed to ameliorate high summer temperatures underground. Reversing platform air flow from impulsion to extraction produced an immediate deterioration in PM air quality, most notably if the higher power setting was maintained, when an especially marked increase in numbers of very fine (submicron) particles was observed and attributed to tunnel air being drawn into the platform. At night, in the absence of trains and platform ventilation, platform air quality improves when tunnel fans are working at reduced power, whatever the flow direction (impulsion/extraction). Inside the air conditioned Barcelona Metro trains (where underground commuters spend most of their time) air quality is markedly better than on the platform, and unchanged A/C filters were observed capable of maintaining a similar reduction in inside train PM for at least three months. [ABSTRACT FROM AUTHOR]

Air quality in subway systems is of interest not only because particulate matter (PM) concentrations can be high, but also because of the peculiarly metalliferous chemical character of the particles, most of which differ radically from those of outdoor ambient air. We report on the oxidative potential (OP) of PM 2.5 samples collected in the Barcelona subway system in different types of stations. The PM chemical composition of these samples showed typically high concentrations of Fe, Total Carbon, Ba, Cu, Mn, Zn and Cr sourced from rail tracks, wheels, catenaries, brake pads and pantographs. Two toxicological indicators of oxidative activity, ascorbic acid (AA) oxidation (expressed as OP AA μg −1 or OP AA m −3 ) and glutathione (GSH) oxidation (expressed as OP GSH μg −1 or OP GSH m −3 ), showed low OP for all samples (compared with outdoor air) but considerable variation between stations (0.9–2.4 OP AA μg −1 ; 0.4–1.9 OP GSH μg −1 ). Results indicate that subway PM toxicity is not related to variations in PM 2.5 concentrations produced by ventilation changes, tunnel works, or station design, but may be affected more by the presence of metallic trace elements such as Cu and Sb sourced from brakes and pantographs. The OP assays employed do not reveal toxic effects from the highly ferruginous component present in subway dust. [ABSTRACT FROM AUTHOR]

With the objective of estimating the impact of harbour activities on ambient PM 10 and PM 2.5 levels at the urban area of Barcelona, a one year long monitoring campaign was carried out in the context of the European APICE project (MED-FEDER-EC). This campaign was simultaneously conducted at the port and a central urban background site. A detailed PM 10 and PM 2.5 chemical speciation analysis was carried out with samples from both sites. Subsequently, a source apportionment analysis by means of the PMF receptor model was performed. Six common factors were identified, explaining local to regional emission sources (fuel oil combustion, industrial emissions, mineral-road dust resuspension, and road traffic emissions) and aerosol formation/transformation processes (secondary aerosols including ammonium sulphate and organic aerosols, and a mixed source accounting for aged sea spray and secondary nitrate). Around 50–55% PM 10 and PM 2.5 measured at the port was attributed to harbour activities: mineral matter from road dust and construction works of a new port area, vehicle traffic and fuel oil combustion. The estimated contribution of harbour emissions to the urban background reached 9–12% for PM 10 and 11–15% for PM 2.5 and is linked to primary emissions from fuel oil combustion but also to the formation of secondary aerosols. It becomes relevant to highlight the significantly higher contribution of secondary aerosols at the urban background when compared with the harbour site. Our hypothesis points to the fast formation of secondary ammonium sulphate within the city, after the reaction of SO 2 /H 2 SO 4 transported by sea breezes with NH 3 , which is emitted in large amounts in Barcelona; and also to the enhanced formation of secondary organic aerosols within the city. This study broadens our knowledge on atmospheric phenomenology in urban Mediterranean cities and claims for effective abatement strategies focused on maritime practises, in agreement with the driving axis of the APICE project. [ABSTRACT FROM AUTHOR]

Sampling campaigns using the same equipment and methodology were conducted to assess and compare the air quality at three South European subway systems (Barcelona, Athens and Oporto), focusing on concentrations and chemical composition of PM 2.5 on subway platforms, as well as PM 2.5 concentrations inside trains. Experimental results showed that the mean PM 2.5 concentrations widely varied among the European subway systems, and even among different platforms within the same underground system, which might be associated to distinct station and tunnel designs and ventilation systems. In all cases PM 2.5 concentrations on the platforms were higher than those in the urban ambient air, evidencing that there is generation of PM 2.5 associated with the subway systems operation. Subway PM 2.5 consisted of elemental iron, total carbon, crustal matter, secondary inorganic compounds, insoluble sulphate, halite and trace elements. Of all metals, Fe was the most abundant, accounting for 29–43% of the total PM 2.5 mass (41–61% if Fe 2 O 3 is considered), indicating the existence of an Fe source in the subway system, which could have its origin in mechanical friction and wear processes between rails, wheels and brakes. The trace elements with the highest enrichment in the subway PM 2.5 were Ba, Cu, Mn, Zn, Cr, Sb, Sr, Ni, Sn, Co, Zr and Mo. Similar PM 2.5 diurnal trends were observed on platforms from different subway systems, with higher concentrations during subway operating hours than during the transport service interruption, and lower levels on weekends than on weekdays. PM 2.5 concentrations depended largely on the operation and frequency of the trains and the ventilation system, and were lower inside the trains, when air conditioning system was operating properly, than on the platforms. However, the PM 2.5 concentrations increased considerably when the train windows were open. The PM 2.5 levels inside the trains decreased with the trains passage in aboveground sections. [ABSTRACT FROM AUTHOR]

Ambient ultrafine particle number concentrations (PNC) have inhomogeneous spatio-temporal distributions and depend on a number of different urban factors, including background conditions and distant sources. This paper quantitatively compares exposure to ambient ultrafine particles at urban schools in two cities in developed countries, with high insolation climatic conditions, namely Brisbane (Australia) and Barcelona (Spain). The analysis used comprehensive indoor and outdoor air quality measurements at 25 schools in Brisbane and 39 schools in Barcelona. PNC modes were analysed with respect to ambient temperature, land use and urban characteristics, combined with the measured elemental carbon concentrations, NO x (Brisbane) and NO 2 (Barcelona). The trends and modes of the quantified weekday average daily cycles of ambient PNC exhibited significant differences between the two cities. PNC increases were observed during traffic rush hours in both cases. However, the mid-day peak was dominant in Brisbane schools and had the highest contribution to total PNC for both indoors and outdoors. In Barcelona, the contribution from traffic was highest for ambient PNC, while the mid-day peak had a slightly higher contribution for indoor concentrations. Analysis of the relationships between PNC and land use characteristics in Barcelona schools showed a moderate correlation with the percentage of road network area and an anti-correlation with the percentage of green area. No statistically significant correlations were found for Brisbane. Overall, despite many similarities between the two cities, school-based exposure patterns were different. The main source of ambient PNC at schools was shown to be traffic in Barcelona and mid-day new particle formation in Brisbane. The mid-day PNC peak in Brisbane could have been driven by the combined effect of background and meteorological conditions, as well as other local/distant sources. The results have implications for urban development, especially in terms of air quality mitigation and management at schools. [ABSTRACT FROM AUTHOR]

Access to detailed comparisons in air quality variations encountered when commuting through a city offers the urban traveller more informed choice on how to minimise personal exposure to inhalable pollutants. In this study we report on an experiment designed to compare atmospheric contaminants inhaled during bus, subway train, tram and walking journeys through the city of Barcelona. Average number concentrations of particles 10-300 nm in size, N , are lowest in the commute using subway trains ( N <2.5×10 4 part. cm −3 ), higher during tram travel and suburban walking (2.5×10 4 cm −3 < N <5.0×10 4 cm −3 ), and highest in diesel bus or walking in the city centre ( N >5.0×10 4 cm −3 ), with extreme transient peaks at busy traffic crossings commonly exceeding 1.0×10 5 cm −3 and accompanied by peaks in Black Carbon and CO. Subway particles are coarser (mode 90 nm) than in buses, trams or outdoors (<70 nm), and concentrations of fine particulate matter (PM 2.5 ) and Black Carbon are lower in the tram when compared to both bus and subway. CO 2 levels in public transport reflect passenger numbers, more than tripling from outdoor levels to >1200 ppm in crowded buses and trains. There are also striking differences in inhalable particle chemistry depending on the route chosen, ranging from aluminosiliceous at roadsides and near pavement works, ferruginous with enhanced Mn, Co, Zn, Sr and Ba in the subway environment, and higher levels of Sb and Cu inside the bus. We graphically display such chemical variations using a ternary diagram to emphasise how “air quality” in the city involves a consideration of both physical and chemical parameters, and is not simply a question of measuring particle number or mass. [ABSTRACT FROM AUTHOR]

Legislation controlling vehicle emissions has been credited with a general downward trend in NO x (NO 2 +NO) concentrations in Europe since the 1990's. However, recent studies suggest that traffic (roadside) (TR) NO 2 concentrations have not decreased as expected, and in some cases increased, most likely due to the use of oxidation catalysts and particle filters in diesel vehicles (EURO III, IV, V, VI). In this study we describe the time trends in NO x , NO 2 and NO concentrations in 9 European cities comparing TR and urban background (UB) monitoring locations. In each city, we collected hourly city-specific NO x , NO, and NO 2 data from one TR and one UB monitoring site for each year. We describe hourly, weekly, seasonal and inter-annual patterns for periods corresponding to the implementation dates of various EURO vehicle emission standards regulating NO x emissions. The diurnal patterns in all 9 cities strongly reflected morning and evening traffic. In addition, lower weekend concentrations were observed. The NO x concentrations from the TR sites remain unchanged in the majority of the cities over the study period. When stratified by 3 time periods according to the implementation of the EURO standards, an increasing NO 2 /NO x ratio in 7/9 cities with time was noted. However, over the same time period the NO/NO 2 ratio decreased in 8/9 cities. A permanent inversion of the NO/NO 2 ratio was observed to occur in 2003 in 5/9 cities. Our analyses of temporal and diurnal patterns of NO x in European cities show reductions in concentrations consistent with reductions in primary emissions likely arising from the implementation of successive EURO standards. The generally constant or increasing NO 2 concentrations in the majority of the cities assessed over the study period underline the need of further regulative measures to meet the air quality standards and consequently to minimise adverse effects on human health. The ongoing collection and analysis of pollution concentrations across the EU is recommended to monitor trends in pollutants associated with adverse health effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] Only few in vivo toxicity and epidemiological studies focused specifically on non-exhaust sources. [•] Further experiments are needed to better separate individual contributions and health effects. [•] Need of understanding of the interaction between road surface texture, moisture, chemistry, dust load and dust emission. [•] Poor emission inventorying on resuspension and heavy metals. [•] The optimal mitigation strategy for each climatic region is still unknown. [Copyright &y& Elsevier]

Abstract: Shipping emissions are currently increasing and will most likely continue to do so in the future due to the increase of global-scale trade. Ship emissions have the potential to contribute to air quality degradation in coastal areas, in addition to contributing to global air pollution. With the aim to quantify the impacts of shipping emissions on urban air quality in coastal areas in Europe, an in depth literature review was carried out focussing on particulate matter and gaseous pollutants but also reviewing the main chemical tracers of shipping emissions, the particle size distribution of ship-derived particulates and their contributions to population exposure and atmospheric deposition. Mitigation strategies were also addressed. In European coastal areas, shipping emissions contribute with 1–7% of ambient air PM10 levels, 1–14% of PM2.5, and at least 11% of PM1. Contributions from shipping to ambient NO2 levels range between 7 and 24%, with the highest values being recorded in the Netherlands and Denmark. Impacts from shipping emissions on SO2 concentrations were reported for Sweden and Spain. Shipping emissions impact not only the levels and composition of particulate and gaseous pollutants, but may also enhance new particle formation processes in urban areas. [Copyright &y& Elsevier]

Abstract: An artificial neural network (ANN) was developed and tested to forecast PM10 daily concentration in two contrasted environments in NE Spain, a regional background site (Montseny), and an urban background site (Barcelona-CSIC), which was highly influenced by vehicular emissions. In order to predict 24-h average PM10 concentrations, the artificial neural network previously developed by Caselli et al. (2009) was improved by using hourly PM concentrations and deterministic factors such as a Saharan dust alert. In particular, the model input data for prediction were the hourly PM10 concentrations 1-day in advance, local meteorological data and information about air masses origin. The forecasted performance indexes for both sites were calculated and they showed better results for the regional background site in Montseny (R2 =0.86, SI=0.75) than for urban site in Barcelona (R2 =0.73, SI=0.58), influenced by local and sometimes unexpected sources. Moreover, a sensitivity analysis conducted to understand the importance of the different variables included among the input data, showed that local meteorology and air masses origin are key factors in the model forecasts. This result explains the reason for the improvement of ANN's forecasting performance at the Montseny site with respect to the Barcelona site. Moreover, the artificial neural network developed in this work could prove useful to predict PM10 concentrations, especially, at regional background sites such as those on the Mediterranean Basin which are primarily affected by long-range transports. Hence, the artificial neural network presented here could be a powerful tool for obtaining real time information on air quality status and could aid stakeholders in their development of cost-effective control strategies. [Copyright &y& Elsevier]

Abstract: This work presents a summary of the results obtained from a study of the impact of African dust on levels of atmospheric suspended particulate matter registered among different monitoring sites in the Madrid Air Basin, in the centre of the Iberian Peninsula. African dust outbreaks were identified over the period 2001–2008. Lidar measurements helped to assess the temporal evolution of the dust layers and subsequent impact on the surface boundary layer. Monthly trends were analyzed, revealing a late spring/summer maximum occurrence of episodes. The most common synoptic meteorological situations causing the transport of the African dusty air masses were also identified over the seasons. Time series of particulate matter daily concentrations recorded across Air Quality Network monitoring stations and sampling campaigns were collected and analysed. Our results show the contribution of mineral dust to PM10 (particulate matter lower than 10μm, aerodynamic diameter) during African dust outbreaks to be significantly high at rural and urban sites of the Madrid Air Basin, giving rise to exceedances of the PM10 daily limit value (50μg/m3). This result is especially relevant since European directive 2008/50/EC on air quality, takes into account the potential exceedance of the PM10 daily limit value, due to the transport of natural particles from arid regions. [Copyright &y& Elsevier]

Abstract: In spite of the high air quality and health relevance of PM emissions from road dust resuspension in large cities, very little is known on their temporal variability, severely hampering a reliable description of population exposure by dispersion models. We have experimentally monitored the mobile dust load (only inhalable fraction) in two different European urban environments resulting in the first empirical description of the temporal variation of road dust emission strength. In Central (The Netherlands) and Southern (Spain) European environments the loadings of mobile road dust particles <10 μm were found to be generally constant on a day-to-day scale, except during and in the hours immediately after rain events when the mobility of particles drops dramatically to values close to zero. After the rain event the mobile dust load increases exponentially tending to reach again the maximum value, result of the equilibrium between mobilization/buildup of dust and moistening/resuspension processes. The mobilization/buildup of particles smaller than 10 μm was found to be three times faster in Barcelona than in Utrecht, in relation to higher solar radiation. In Barcelona the recovery of mobile road dust reached 50%, 75%, and 90% of the maximum value after 8, 16 and 27 h, respectively. These values were independent of amounts of rain. In Utrecht the same thresholds were reached after, 28, 55 and 90 h, respectively. Our observations may suggest that, for reducing road dust emissions, light but frequent moistening of roads might be more effective than intensive occasional cleanings. [Copyright &y& Elsevier]

Measurements of particle number concentration (N), black carbon (BC), and PM10, PM2.5, and PM1 levels and speciation were carried out at an urban background monitoring site in Barcelona. Daily variability of all aerosol monitoring parameters was highly influenced by road traffic emissions and meteorology. The levels of N, BC, PMX, CO, NO, and NO2 increased during traffic rush hours, reflecting exhaust, and non-exhaust traffic emissions and then decreased by the effect of breezes and the reduction of traffic intensity. PM2.5-10 levels did not decrease during the day as a result of dust resuspension by traffic and wind. N showed a second peak, registered in the afternoon and parallel to O3 levels and solar radiation intensity, that may be attributed to photochemical nucleation of precursor gases. An increasing trend was observed for PM1 levels from 1999 to 2006, related to the increase in the traffic flow and the diesel fleet in Barcelona. PM composition was highly influenced by road traffic emissions, with exhaust emissions being an important source of PM1 and dust resuspension processes of PM2.5-10, respectively. [ABSTRACT FROM AUTHOR]

Source apportionment analyses were carried out by means of receptor modeling techniques to determine the contribution of major fine particulate matter (PM2.5) sources found at six sites in Mexico City. Thirty-six source profiles were determined within Mexico City to establish the fingerprints of particulate matter sources. Additionally, the profiles under the same source category were averaged using cluster analysis and the fingerprints of 10 sources were included. Before application of the chemical mass balance (CMB), several tests were carried out to determine the best combination of source profiles and species used for the fitting. CMB results showed significant spatial variations in source contributions among the six sites that are influenced by local soil types and land use. On average, 24-hr PM2.5 concentrations were dominated by mobile source emissions (45%), followed by secondary inorganic aerosols (16%) and geological material (17%). Industrial emissions representing oil combustion and incineration contributed less than 5%, and their contribution was higher at the industrial areas of Tlalnepantla (11%) and Xalostoc (8%). Other sources such as cooking, biomass burning, and oil fuel combustion were identified at lower levels. A second receptor model (principal component analysis, [PCA]) was subsequently applied to three of the monitoring sites for comparison purposes. Although differences were obtained between source contributions, results evidence the advantages of the combined use of different receptor modeling techniques for source apportionment, given the complementary nature of their results. Further research is needed in this direction to reach a better agreement between the estimated source contributions to the particulate matter mass. [ABSTRACT FROM AUTHOR]

The present investigation, carried out as a case study in a typical major city situated in a European coal combustion region (Krakow, Poland), aims at quantifying the impact on the urban air quality of residential heating by coal combustion in comparison with other potential pollution sources such as power plants, industry, and traffic. Emissions were measured for 20 major sources, including small stoves and boilers, and the particulate matter (PM) was analyzed for 52 individual compounds together with outdoor and indoor PM10 collected during typical winter pollution episodes. The data were analyzed using chemical mass balance modeling (CMB) and constrained positive matrix factorization (CMF) yielding source apportionments for PM10 B(a)P, and other regulated air pollutants namely Cd, Ni, As, and Pb. The results are potentially very useful for planning abatement strategies in all areas of the world, where coal combustion in small appliances is significant. During the studied pollution episodes in Krakow, European air quality limits were exceeded with up to a factor 8 for PM10 and up to a factor 200 for B(a)P. The levels of these air pollutants were accompanied by high concentrations of azaarenes, known markers for inefficient coal combustion. The major culprit for the extreme pollution levels was demonstrated to be residential heating by coal combustion in small stoves and boilers (>50% for PM10 and >90% B(a)P), whereas road transport (<10% for PM10 and <3% for B(a)P), and industry (4-15% for PM10 and <6% for B(a)P) played a lesser role. The indoor PM10 and B(a)P concentrations were at high levels similar to those of outdoor concentrations and were found to have the same sources as outdoors. The inorganic secondary aerosol component of PM10 amounted to around 30%, which for a large part may be attributed to the industrial emission of the precursors SO2 and NOx. [ABSTRACT FROM AUTHOR]

Remodelling works are frequent in harbour areas, given that they must adapt to rapidly changing market requirements. Depending on their nature (construction, demolition, etc.), these works may be carried out during long periods of time and thus exert a significant impact on the air quality at the harbours and their surroundings. The air quality at the Valencia harbour was studied during an enlargement project. Four sampling stations aimed to cover the major dust-emitting activities in the harbour. In addition, a sampling campaign was carried out to collect dust materials at their emission sources (e.g., loading and unloading of clinker and petroleum coke, as well as the enlargement works). Differences obtained between PM levels at the monitoring sites were correlated with the distance between sampling stations and enlargement works and/or harbour operations, as well as with the preferential wind direction. In all cases, the days with the highest PM_10 levels were linked to wind directions coinciding with the location of the enlargement works or the clinker and petroleum coke stocks. Classic source apportionment methodologies (PCA and CMB) were applied to the data, but their interpretation was complex due to the similar chemical signatures of PM originating from direct and fugitive emissions from stocked materials (e.g., clinker), and the enlargement works. To overcome this difficulty, a novel non-statistical approach was used to obtain quantitative estimations of the contributions from sources (petroleum coke and clinker), based on the correlation between specific PM components (e.g., carbonaceous species) and source tracers (e.g., V). Finally, a qualitative test using phenolphthalein was devised to identify the presence of clinker on the filters, which provided positive results. This novel tracer approach is thus recommended for harbour authorities. [Copyright &y& Elsevier]

This paper synthesizes data on aerosol (or particulate matter, PM) chemical characteristics, which were obtained in European aerosol research activities at natural, rural, near-city, urban, and kerbside sites over the past decade. It includes only two (nearby) sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. PM chemical compositions are compared with the PM mass concentrations in PM10, PM2.5, and further size resolved PM fractions (chemical mass closure). Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 24 sites in Europe were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn among which are the following.Organic matter appears to be the major component of PM10 and PM2.5, except at natural and rural background sites, where sulphate contribution may be larger. Mineral dust shows up as a major component of PM10 at kerbside sites. Black carbon contributes 5–10% to PM2.5 and somewhat less to PM10 at all sites, including the natural background sites. Its contribution seems higher (15–20%) at some of the kerbside sites, but these data may be affected by analytical artefacts. On days when PM10 >50 μg m−3, nitrate concentrations can overtake organic matter concentrations in PM10 and PM2.5. High PM concentration episodes are often observed in cold periods, when the pollutant dispersion is least. Measurements indicate that the condensation in the particle phase of semi-volatile species like nitrate and (unspecified) organics is also favoured by cold temperatures. In particles with a diameter <150 nm (i.e., most atmospheric particles), organic matter and black carbon are by far the major components.More data are known to be available within the scientific community, which could enrich the present data set and strengthen the conclusions made above. Most of them are not made available yet. The investment in new approaches, which would bridge the technological gap between scientific measurements and regulatory monitoring networks, is strongly needed. [Copyright &y& Elsevier]

This paper synthesizes data on aerosol (particulate matter, PM) physical characteristics, which were obtained in European aerosol research activities at free-troposphere, natural, rural, near-city, urban, and kerbside sites over the past decade. It covers only two sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. The data include PM10 and/or PM2.5 mass concentrations, and aerosol particle size distributions. Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 31 sites in Europe (called “The Network”) were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn as follows:Background annual average PM10 and PM2.5 mass concentrations for continental Europe are 7.0±4.1 and 4.8±2.4 μg m−3, respectively.The EU 2005 annual average PM10 standard of 40 μg m−3 is exceeded at a few sites in The Network. At all near city, urban and kerbside sites, the EU 2010 annual average PM10 standard of 20 μg m−3, as well as the US-EPA annual average PM2.5 standard of 15 μg m−3 are exceeded. In certain regions, PM10 and PM2.5 in cities are strongly affected by the regional aerosol background.There is no “universal” (i.e. valid for all sites) ratio between PM2.5 and PM10 mass concentrations, although fairly constant ratios do exist at individual sites. There is no universal correlation between PM mass concentration on the one hand, and total particle number concentration on the other hand, although a ‘baseline’ ratio between number and mass is found for sites not affected by local emissions. This paper is the first part of two companion papers of which the second part describes chemical characteristics. [Copyright &y& Elsevier]

We assessed 2005─2018 data series of NO, NO 2 , and O 3 surface measurements, meteorological data and remote sensing of tropospheric NO 2 by OMI-NASA in the Guadalquivir Valley (GV, Andalucía). The GV is one of the Spanish atmospheric basins with the most exceedances of the EU's hourly O 3 information threshold (180 μg O 3 m−3). We aimed to deepen understanding of the phenomenology of O 3 episodes in the GV, quantify local and regional contributions from long-range transported O 3 , and identify key episodes and atmospheric parameters to validate modeling tools for the assessment of O 3 abatement policies with acceptable uncertainty levels. A significant proportion of acute O 3 episodes (defined as episodes of 1–7 consecutive days, when very high hourly O 3 concentrations are recorded) in the GV is caused by long-range transported contributions in addition to the regional accumulation of pollution which is, in most cases, driven by the vertical recirculation of air masses, as described in several basins of the Iberian Peninsula. In these episodes, high O 3 arises from the fumigation of high reserve recirculated strata as the boundary layer grows, sea-breeze transport of O 3 and precursors, local formation, and long-range transport. The most acute episodes are recorded close to Sevilla, probably because of the mix of precursors from the urban areas and the petrochemical industry of Huelva. We quantified the average O 3 contributions to O 3 concentrations in Sevilla during these episodes as 53% background levels before the episode (defined as the concentration measured at the coastal remote sites at the beginning of the pollution episode, when the Atlantic air masses transport background O 3 from synoptic air mass transport), 22% accumulation throughout the episode, and 25% of daily local and regional contribution to the average 8h-daily maxima (157 μg O 3 m−3). Thus, a maximum decreasing potential of 74 μg O 3 m−3 (47%) of the average 8h-daily maxima can be expected when applying abatement measures to reduce O 3 precursors in the day before the start of an episode and until the end of the episode. Our results demonstrate that it is crucial to meteorologically forecast the occurrence of such recirculation and accumulation processes in the GV basin. • A 2005─2018 evaluation of high ozone pollution in the Guadalquivir Valley. • Frequent ozone accumulation driven by vertical recirculation in the Valley. • Information threshold exceeded in Sevilla (>3 h yr−1), target value in the Valley (>50 day yr−1). • Quantification of O 3 contributions during the most acute episodes in Sevilla. • Significant maximum O 3 abatement potential: 47% (74 μg m−3) of max 8h-daily concentration. [ABSTRACT FROM AUTHOR]

• Hazard prediction of particulate matter (PM) by the Machine learning (ML) models. • Selection of key features using the simulated annealing (SA) method. • Good performance of the ML models in PM modeling (Accuracy > 87%; Precision > 86%). Air pollution, and especially atmospheric particulate matter (PM), has a profound impact on human mortality and morbidity, environment, and ecological system. Accordingly, it is very relevant predicting air quality. Although the application of the machine learning (ML) models for predicting air quality parameters, such as PM concentrations, has been evaluated in previous studies, those on the spatial hazard modeling of them are very limited. Due to the high potential of the ML models, the spatial modeling of PM can help managers to identify the pollution hotspots. Accordingly, this study aims at developing new ML models, such as Random Forest (RF), Bagged Classification and Regression Trees (Bagged CART), and Mixture Discriminate Analysis (MDA) for the hazard prediction of PM10 (particles with a diameter less than 10 µm) in the Barcelona Province, Spain. According to the annual PM10 concentration in 75 stations, the healthy and unhealthy locations are determined, and a ratio 70/30 (53/22 stations) is applied for calibrating and validating the ML models to predict the most hazardous areas for PM10. In order to identify the influential variables of PM modeling, the simulated annealing (SA) feature selection method is used. Seven features, among the thirteen features, are selected as critical features. According to the results, all the three-machine learning (ML) models achieve an excellent performance (Accuracy > 87% and precision > 86%). However, the Bagged CART and RF models have the same performance and higher than the MDA model. Spatial hazard maps predicted by the three models indicate that the high hazardous areas are located in the middle of the Barcelona Province more than in the Barcelona's Metropolitan Area. [ABSTRACT FROM AUTHOR]