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• The phenomenology of urban ultrafine particles in 16 cities of Europe is presented. • N to S&E Europe increasing urban background concentration trends are evidenced. • Road traffic emissions is the main source of ultrafine particles in urban Europe. • High midday concentrations independent of traffic influence occur in many cities. • There is an urgent need to harmonize measurements and making the data open. The 2017–2019 hourly particle number size distributions (PNSD) from 26 sites in Europe and 1 in the US were evaluated focusing on 16 urban background (UB) and 6 traffic (TR) sites in the framework of R esearch I nfrastructures services reinforcing air quality monitoring capacities in European URBAN & industrial area S (RI-URBANS) project. The main objective was to describe the phenomenology of urban ultrafine particles (UFP) in Europe with a significant air quality focus. The varying lower size detection limits made it difficult to compare PN concentrations (PNC), particularly PN 10-25 , from different cities. PNCs follow a TR > UB > Suburban (SUB) order. PNC and Black Carbon (BC) progressively increase from Northern Europe to Southern Europe and from Western to Eastern Europe. At the UB sites, typical traffic rush hour PNC peaks are evident, many also showing midday-morning PNC peaks anti-correlated with BC. These peaks result from increased PN 10-25 , suggesting significant PNC contributions from nucleation, fumigation and shipping. Site types to be identified by daily and seasonal PNC and BC patterns are: (i) PNC mainly driven by traffic emissions, with marked correlations with BC on different time scales; (ii) marked midday/morning PNC peaks and a seasonal anti-correlation with PNC/BC; (iii) both traffic peaks and midday peaks without marked seasonal patterns. Groups (ii) and (iii) included cities with high insolation. PNC, especially PN 25-800 , was positively correlated with BC, NO 2 , CO and PM for several sites. The variable correlation of PNSD with different urban pollutants demonstrates that these do not reflect the variability of UFP in urban environments. Specific monitoring of PNSD is needed if nanoparticles and their associated health impacts are to be assessed. Implementation of the CEN-ACTRIS recommendations for PNSD measurements would provide comparable measurements, and measurements of <10 nm PNC are needed for full evaluation of the health effects of this size fraction. [ABSTRACT FROM AUTHOR]

Ultrafine particles (UFP, those with diameters ≤ 100 nm), have been reported to potentially penetrate deeply into the respiratory system, translocate through the alveoli, and affect various organs, potentially correlating with increased mortality. The aim of this study is to assess long-term trends (5–11 years) in mostly urban UFP concentrations based on measurements of particle number size distributions (PNSD). Additionally, concentrations of other pollutants and meteorological variables were evaluated to support the interpretations. PNSD datasets from 12 urban background (UB), 5 traffic (TR), 3 suburban background (SUB) and 1 regional background (RB) sites in 15 European cities and 1 in the USA were evaluated. The non-parametric Theil-Sen's method was used to detect monotonic trends. Meta-analyses were carried out to assess the overall trends and those for different environments. The results showed significant decreases in NO, NO 2 , BC, CO, and particle concentrations in the Aitken (25–100 nm) and the Accumulation (100–800 nm) modes, suggesting a positive impact of the implementation of EURO 5/V and 6/VI vehicle standards on European air quality. The growing use of Diesel Particle Filters (DPFs) might also have clearly reduced exhaust emissions of BC, PM, and the Aitken and Accumulation mode particles. However, as reported by prior studies, there remains an issue of poor control of Nucleation mode particles (smaller than 25 nm), which are not fully reduced with current DPFs, without emission controls for semi-volatile organic compounds, and might have different origins than road traffic. Thus, contrasting trends for Nucleation mode particles were obtained across the cities studied. This mode also affected the UFP and total PNC trends because of the high proportion of Nucleation mode particles in both concentration ranges. It was also found that the urban temperature increasing trends might have also influenced those of PNC, Nucleation and Aitken modes. [ABSTRACT FROM AUTHOR]

Background: The implementation of emission mitigation policies in Europe over the last two decades has generally improved the air quality, which resulted in lower aerosol particle mass, particle number, and black carbon mass concentration. However, little is known whether the decreasing particle concentrations at a lower-altitude level can be observed in the free troposphere (FT), an important layer of the atmosphere, where aerosol particles have a longer lifetime and may affect climate dynamics. In this study, we used data from two high-Alpine observatories, Zugspitze-Schneefernerhaus (ZSF) and Jungfraujoch (JFJ), to assess the long-term trends on size-resolved particle number concentrations (PNCs) and equivalent black carbon (eBC) mass concentration separated for undisturbed lower FT conditions and under the influence of air from the planetary boundary layer (PBL) from 2009 to 2018. Results: The FT and PBL-influenced conditions were segregated for both sites. We found that the FT conditions in cold months were more prevalent than in warm months, while the measured aerosol parameters showed different seasonal patterns for the FT and PBL-influenced conditions. The pollutants in the PBL-influenced condition have a higher chance to be transported to high-altitudes due to the mountainous topography, leading to a higher concentration and more distinct seasonal variation, and vice versa. The long-term trends of the measured aerosol parameters were evaluated and the decreased aerosol concentrations were observed for both FT and PBL-influenced conditions. The observed decreasing trends in eBC concentration in the PBL-influenced condition are well consistent with the reported trends in total BC emission in Germany and Switzerland. The decreased concentrations in the FT condition suggest that the background aerosol concentration in the lower FT over Central Europe has correspondingly decreased. The change of back trajectories in the FT condition at ZSF and JFJ was further evaluated to investigate the other possible drivers for the decreasing trends. Conclusions: The background aerosol concentration in the lower FT over Central Europe has significantly decreased during 2009–2018. The implementation of emission mitigation policies is the most decisive factor and the decrease of the regional airmass occurrence over Central Europe also has contributed to the decreasing trends. [ABSTRACT FROM AUTHOR]

The main objective of this work is the study of the impact of windblown dust, sea-salt aerosol and biogenic emissions on particle pollution levels in Europe. The Natural Emissions MOdel (NEMO) and the modelling system consisted of the Weather Research and Forecasting model (WRF) and the Comprehensive Air Quality model with extensions (CAMx) were applied in a 30 km horizontal resolution grid, which covered Europe and the adjacent areas for the year 2009. Air quality simulations were performed for different emission scenarios in order to study the contribution of each natural emission source individually and together to air quality levels in Europe. The simulations reveal that the exclusion of windblown dust emissions decreases the mean seasonal PM10 levels by more than 3.3 μg/m 3 (∼20%) in the Eastern Mediterranean during winter while an impact of 3 μg/m 3 was also found during summer. The results suggest that sea-salt aerosol has a significant effect on PM levels and composition. Eliminating sea-salt emissions reduces PM10 seasonal concentrations by around 10 μg/m 3 in Mediterranean Sea during summer while a decrease of up to 6 μg/m 3 is found in Atlantic Ocean during autumn. Sea-salt particles also interact with the anthropogenic component and therefore their absence in the atmosphere decreases significantly the nitrates in aerosols where shipping activities are present. The exclusion of biogenic emissions in the model runs leads to a significant reduction of secondary organic aerosols of more than 90% while an increase in PM2.5 levels in central Europe and Eastern Mediterranean is found due to their interaction with anthropogenic component. [ABSTRACT FROM AUTHOR]

In Europe mainly at winter season the PM levels exceed air quality limits, which correlated with the operation of solid-fired boilers. More and more people are returning to using these devices due to energy shortage caused by the pandemic and regional conflicts. In addition, the phenomena of co-burning fuels and municipal waste in residential boilers in primarily fuel poverty households increases further the amount of pollutants in the atmosphere. This study aims to correlate the quantity and quality of air pollutants with the type of fuel (wood and wastes) burned. Combustion experiments were conducted using oak fuel mixed with three waste groups: (1) plastics (PP, HDPE, PET); (2) textiles (polyester—PES, cotton—COT); and (3) papers (cardboard—CARD, glossy coated paper—GCP, 84C/PAP). The addition of waste to wood fuel altered the morphology of emitted particles. While waste burning doesn't always increase particle quantity, it significantly raises PAH concentrations. A strong relationship exists between waste type, particle morphology, and PAH quality, where with lower molecular weight PAHs linked to tar agglomerates and higher ones to soot agglomerates with inorganic crystals. [ABSTRACT FROM AUTHOR]

BACKGROUND: Inhalation is one of the main means of human exposure to polycyclic aromatic hydrocarbons (PAHs) because of their ubiquitous presence in the atmosphere. However, most studies have considered only PAHs found in the particle phase and have omitted the contribution of the gas-phase PAHs to the risk. OBJECTIVE: We estimated the lifetime lung cancer risk from PAH exposure by inhalation in people living next to the largest chemical site in Southern Europe and the Mediterranean area. METHODS: We determined 18 PAHs in the atmospheric gas and particle phase. We monitored the PAHs for 1 year in three locations near the chemical site in different seasons. We used toxic equivalence factors to calculate benzo[a]pyrene (BaP) equivalents (BaP-eq) for individual PAHs and applied the World Health Organization unit risk (UR) for BaP (UR = 8.7 × 10-5) to estimate lifetime cancer risks due to PAH exposures. RESULTS: We observed some spatial and seasonal variability in PAH concentrations. The contribution of gas-phase PAHs to the total BaP-eq value was between 34% and 86%. The total estimated average lifetime lung cancer risk due to PAH exposure in the study area was 1.2 × 10-4. CONCLUSIONS: The estimated risk was higher than values recommended by the World Health Organization and U.S. Environmental Protection Agency but lower than the threshold value of 10-3 that is considered an indication of definite risk according to similar risk studies. The results also showed that risk may be underestimated if the contributions of gas-phase PAHs are not considered. [ABSTRACT FROM AUTHOR]

Featured Application: Key conclusions and recommendations are proposed to enlighten decision makers in view of the next regulations on vehicle emissions in Europe and worldwide through the synergistic contexts of air quality and climate change. Airborne particulate matter (PM) is a pollutant of concern not only because of its adverse effects on human health but also on visibility and the radiative budget of the atmosphere. PM can be considered as a sum of solid/liquid species covering a wide range of particle sizes with diverse chemical composition. Organic aerosols may be emitted (primary organic aerosols, POA), or formed in the atmosphere following reaction of volatile organic compounds (secondary organic aerosols, SOA), but some of these compounds may partition between the gas and aerosol phases depending upon ambient conditions. This review focuses on carbonaceous PM and gaseous precursors emitted by road traffic, including ultrafine particles (UFP) and polycyclic aromatic hydrocarbons (PAHs) that are clearly linked to the evolution and formation of carbonaceous species. Clearly, the solid fraction of PM has been reduced during the last two decades, with the implementation of after-treatment systems abating approximately 99% of primary solid particle mass concentrations. However, the role of brown carbon and its radiative effect on climate and the generation of ultrafine particles by nucleation of organic vapour during the dilution of the exhaust remain unclear phenomena and will need further investigation. The increasing role of gasoline vehicles on carbonaceous particle emissions and formation is also highlighted, particularly through the chemical and thermodynamic evolution of organic gases and their propensity to produce particles. The remaining carbon-containing particles from brakes, tyres and road wear will still be a problem even in a future of full electrification of the vehicle fleet. Some key conclusions and recommendations are also proposed to support the decision makers in view of the next regulations on vehicle emissions worldwide. [ABSTRACT FROM AUTHOR]

In many large cities of Europe standard air quality limit values of particulate matter (PM) are exceeded. Emissions from road traffic and biomass burning are frequently reported to be the major causes. As a consequence of these exceedances a large number of air quality plans, most of them focusing on traffic emissions reductions, have been implemented in the last decade. In spite of this implementation, a number of cities did not record a decrease of PM levels. Thus, is the efficiency of air quality plans overestimated? Do the road traffic emissions contribute less than expected to ambient air PM levels in urban areas? Or do we need a more specific metric to evaluate the impact of the above emissions on the levels of urban aerosols? This study shows the results of the interpretation of the 2009 variability of levels of PM, Black Carbon (BC), aerosol number concentration (N) and a number of gaseous pollutants in seven selected urban areas covering road traffic, urban background, urban-industrial, and urban-shipping environments from southern, central and northern Europe. The results showed that variations of PM and N levels do not always reflect the variation of the impact of road traffic emissions on urban aerosols. However, BC levels vary proportionally with those of traffic related gaseous pollutants, such as CO, NO2 and NO. Due to this high correlation, one may suppose that monitoring the levels of these gaseous pollutants would be enough to extrapolate exposure to traffic-derived BC levels. However, the BC/CO, BC/NO2 and BC/NO ratios vary widely among the cities studied, as a function of distance to traffic emissions, vehicle fleet composition and the influence of other emission sources such as biomass burning. Thus, levels of BC should be measured at air quality monitoring sites. During morning traffic rush hours, a narrow variation in the N/BC ratio was evidenced, but a wide variation of this ratio was determined for the noon period. Although in central and northern Europe N and BC levels tend to vary simultaneously, not only during the traffic rush hours but also during the whole day, in urban background stations in southern Europe maximum N levels coinciding with minimum BC levels are recorded at midday in all seasons. These N maxima recorded in southern European urban background environments are attributed to midday nucleation episodes occurring when gaseous pollutants are diluted and maximum insolation and O3 levels occur. The occurrence of SO2 peaks may also contribute to the occurrence of midday nucleation bursts in specific industrial or shipping-influenced areas, although at several central European sites similar levels of SO2 are recorded without yielding nucleation episodes. Accordingly, it is clearly evidenced that N variability in different European urban environments is not equally influenced by the same emission sources and atmospheric processes. We conclude that N variability does not always reflect the impact of road traffic on air quality, whereas BC is a more consistent tracer of such an influence. However, N should be measured since ultrafine particles (<100 nm) may have large impacts on human health. The combination of PM10 and BC monitoring in urban areas potentially constitutes a useful approach for air quality monitoring. BC is mostly governed by vehicle exhaust emissions, while PM10 concentrations at these sites are also governed by non-exhaust particulate emissions resuspended by traffic, by midday atmospheric dilution and by other non-traffic emissions. [ABSTRACT FROM AUTHOR]

Can mitigating only particle mass, as the existing air quality measures do, ultimately lead to reduction in ultrafine particles (UFP)? The aim of this study was to provide a broader urban perspective on the relationship between UFP, measured in terms of particle number concentration (PNC) and PM 2.5 (mass concentration of particles with aerodynamic diameter < 2.5 μm) and factors that influence their concentrations. Hourly average PNC and PM 2.5 were acquired from 10 cities located in North America, Europe, Asia, and Australia over a 12-month period. A pairwise comparison of the mean difference and the Kolmogorov-Smirnov test with the application of bootstrapping were performed for each city. Diurnal and seasonal trends were obtained using a generalized additive model (GAM). The particle number to mass concentration ratios and the Pearson's correlation coefficient were calculated to elucidate the nature of the relationship between these two metrics. Results show that the annual mean concentrations ranged from 8.0 × 103 to 19.5 × 103 particles·cm−3 and from 7.0 to 65.8 μg·m−3 for PNC and PM 2.5 , respectively, with the data distributions generally skewed to the right, and with a wider spread for PNC. PNC showed a more distinct diurnal trend compared with PM 2.5 , attributed to the high contributions of UFP from vehicular emissions to PNC. The variation in both PNC and PM 2.5 due to seasonality is linked to the cities' geographical location and features. Clustering the cities based on annual median concentrations of both PNC and PM 2.5 demonstrated that a high PNC level does not lead to a high PM 2.5 , and vice versa. The particle number-to-mass ratio (in units of 109 particles·μg−1) ranged from 0.14 to 2.2, >1 for roadside sites and <1 for urban background sites with lower values for more polluted cities. The Pearson's r ranged from 0.09 to 0.64 for the log-transformed data, indicating generally poor linear correlation between PNC and PM 2.5. Therefore, PNC and PM 2.5 measurements are not representative of each other; and regulating PM 2.5 does little to reduce PNC. This highlights the need to establish regulatory approaches and control measures to address the impacts of elevated UFP concentrations, especially in urban areas, considering their potential health risks. [ABSTRACT FROM AUTHOR]

The concentrations of toluene and dichloromethane in the vicinity of factories that emitted a large amount of toluene or dichloromethane into the atmosphere were determined for the comparison of observed and estimated concentrations using a Gaussian dispersion model (METI-LIS model). Greater concentrations of toluene and dichloromethane than the guideline value described in the Air Quality Guidelines for Europe, second edition, were measured in the vicinity of factories (270 and 470 μ g/m3 for toluene and 510 and 660 μ g/m3 for dichloromethane). Toluene and dichloromethane may have some adverse health effects on the local population in the vicinity of the emission source. Although the estimated concentrations in the vicinity of the emission source by the METI-LIS model involved a large margin of error, the proposed correction approach with only one weekly measurement reduced the estimation error of annual average concentrations. The proposed method could be useful for the management of ambient environment of emission source, due to no difficulty in modifying the input parameters of METI-LIS that required highly specialized knowledge. [ABSTRACT FROM AUTHOR]

Wildfires are a significant source of organic aerosol during summer, with major impacts on air quality and climate. However, studies in Europe suggest a surprisingly low (less than 10%) contribution of biomass burning organic aerosol to average summertime fine particulate matter levels. In this study we combine field measurements and atmospheric chemical transport modeling, to demonstrate that the contribution of wildfires to fine particle levels in Europe during summer is seriously underestimated. Our work suggests that the corresponding contribution has been underestimated by a factor of 4–7 and that wildfires were responsible for approximately half of the total OA in Europe during July 2022. This discrepancy with previous work is due to the rapid physicochemical transformation of these emissions to secondary oxidized organic aerosol with an accompanying loss of its organic chemical fingerprints. These atmospheric reactions lead to a regionally distributed background organic aerosol that is responsible for a significant fraction of the health-related impacts caused by fine particles in Europe and probably in other continents. These adverse health effects can occur hundreds or even thousands of kilometers away from the fires. We estimate that wildfire emissions are responsible for 15–22% of the deaths in Europe due to exposure to fine particulate matter during summer. [ABSTRACT FROM AUTHOR]

Atmospheric sea salt particles affect chemical and physical processes in the atmosphere. These particles provide surface area for condensation and reaction of nitrogen, sulfur, and organic species and are a vehicle for the transport of these species. Additionally, HCl is released from sea salt. Hence, sea salt has a relevant impact on air quality, particularly in coastal regions with high anthropogenic emissions, such as the North Sea region. Therefore, the integration of sea salt emissions in modeling studies in these regions is necessary. However, it was found that sea salt concentrations are not represented with the necessary accuracy in some situations. In this study, three sea salt emission parameterizations depending on different combinations of wind speed, salinity, sea surface temperature, and wave data were implemented and compared: GO03 (Gong, 2003), SP13 (Spada et al., 2013), and OV14 (Ovadnevaite et al., 2014). The aim was to identify the parameterization that most accurately predicts the sea salt mass concentrations at different distances to the source regions. For this purpose, modeled particle sodium concentrations, sodium wet deposition, and aerosol optical depth were evaluated against measurements of these parameters. Each 2-month period in winter and summer 2008 were considered for this purpose. The shortness of these periods limits generalizability of the conclusions on other years. While the GO03 emissions yielded overestimations in the PM10 concentrations at coastal stations and underestimations of those at inland stations, OV14 emissions conversely led to underestimations at coastal stations and overestimations at inland stations. Because of the differently shaped particle size distributions of the GO03 and OV14 emission cases, the deposition velocity of the coarse particles differed between both cases which yielded this distinct behavior at inland and coastal stations. The PM10 concentrations produced by the SP13 emissions generally overestimated the measured concentrations. The sodium wet deposition was generally underestimated by the model simulations but the SP13 cases yielded the least underestimations. Because the model tends to underestimate wet deposition, this result needs to be considered critically. Measurements of the aerosol optical depth (AOD) were underestimated by all model cases in the summer and partly in winter. None of the model cases clearly improved the modeled AODs. Overall, GO03 and OV14 produced the most accurate results, but both parameterizations revealed weaknesses in some situations. [ABSTRACT FROM AUTHOR]

Abstract: The chemical composition of PM10 and PM2.5 was studied during summer and winter sampling campaigns in South and West Europe (Barcelona, Spain, and Ghent, Belgium). The chemical composition of the PM10 aerosol was markedly different in the two regions, even at similar PM10 levels. The chemical composition of PM2.5 showed more similarities. The contribution of mineral matter was higher in Barcelona (on average 12% of the PM2.5 mass), whereas the contribution from sea salt was higher in Ghent (4% of PM2.5). Volatilisation of NH4 + from the filters (negative artefact) was observed in both regions, although the extent of this artefact showed regional differences (0–4% and 22–38% of the NH4 + mass in Ghent and Barcelona, respectively) and had no impact on the compliance with EU limit values. The number of exceedances of the PM10 limit value and an arbitrary PM2.5 limit of 25μgm−3 was calculated by subtracting the mineral fraction (natural or anthropogenic in origin) from the bulk PM load, and this resulted in the elimination of the PM10 exceedances in Barcelona, and a reduction of one out of three exceedances in Ghent. The subtraction of sea-salt aerosol had no effect in Barcelona, and it removed one exceedance in each size fraction in Ghent. Exceedances of the PM10 daily limit value in Ghent coincided with back-trajectories originating from Eastern and Southern European regions. The origin of the exceedances in Barcelona during the campaigns was mostly local. [Copyright &y& Elsevier]

We used the objective analysis method in conjunction with the successive correction method to assimilate MODerate resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data into the Chimère model in order to improve the modeling of fine particulate matter (PM 2.5 ) concentrations and AOD field over Europe. A data assimilation module was developed to adjust the daily initial total column aerosol concentrations based on a forecast-analysis cycling scheme. The model is then evaluated during one-month winter period to examine how such a data assimilation technique pushes the model results closer to surface observations. This comparison showed that the mean biases of both surface PM 2.5 concentrations and the AOD field could be reduced from − 34 to −15% and from −45 to −27%. The assimilation, however, leads to false alarms because of the difficulty in distributing AOD 550 over different particle sizes. The impact of the influence radius is found to be small and depends on the density of satellite data. This work, although preliminary, is important in terms of near-real time air quality forecasting using the Chimère model and can be further developed to improve modeled PM 2.5 and ozone concentrations. [ABSTRACT FROM AUTHOR]

Particulate pollution is a serious concern in developed countries especially in urban and suburban areas where it has adverse effects on human health, exacerbating a wide range of respiratory and vascular illnesses. Data are now available which indicate that similar problems probably occur in countries in transition and may indeed be worse where national air quality standards have been neither set nor monitored. Recently a variety of approaches using both wind tunnel and field measurements have suggested that trees can significantly reduce such adverse effects through their ability to capture pollutant particles. It is clear that species choice, planting design and location relative to pollution source are critical in determining the effectiveness of particle capture by trees. Here we present relative deposition velocities and capture efficiencies of five species used widely in woodland of urban and periurban areas of Europe (Quercus petraea (oak), Alnus glutinosa (alder), Fraxinus excelsior (ash), Acer pseudo-platanus (sycamore) and Pseudotsuga menziesii (Douglas fir)), and for two species being used increasingly in semi-arid regions, (Ficus nitida (weeping fig) and Eucalyptus. globulus (Eucalyptus)). These data are for species not previously worked on and measurements were made at three windspeeds. Deposition velocities and capture efficiencies are compared with those published for other tree species, with the values of deposition velocity ranging from 0.1 to 0.3 cm s -1 at a windspeed of 3 m s -1 to maximum values 2.9 cm s -1 at 9 m s -1 windspeed. Species with more complex stem structure and smaller leaves had greater relative deposition velocities. The use of such data in models to guide species choice and planting design in order to maximise particle removal from urban air are considered. [ABSTRACT FROM AUTHOR]

Ambient particulate matter (PM) is a widespread air pollutant, consisting of a mixture of different particle species suspended in the air that negatively affects human health. Given the generally sparse distribution of in-situ PM measurement networks, spatially-resolved PM estimates are typically derived from Aerosol Optical Depth (AOD) obtained from satellites. However, satellite AOD data over land is affected by several limitations (e.g., data gaps; coarser resolution; higher uncertainty; unavailable or unreliable size fraction information), which weakens the relationship between AOD and PM. We have developed a 0.1 degree resolution daily AOD data set over Europe over the period 2003-2020, based on new Quantile Machine Learning (QML) models. The dataset provides reliable full-coverage AOD along with Fine-mode AOD (fAOD) and Coarse-mode AOD (cAOD), based on AERONET (AErosol RObotic NETwork) site observations and climate and air quality reanalyses. Our results show that the three QML AOD products guarantee better quality with an out-of-sample R2 equal to 0.68 for AOD, 0.66 for fAOD and 0.65 for cAOD, which is 23-92%, 11-13% and 115-132% higher than the corresponding satellite or reanalysis products, respectively. Over 88.8%, 80.5% and 88.6% of QML AOD, fAOD and cAOD predictions fall within ±20% Expected Error (EE) envelopes, respectively. Previous studies reported that Europe is one of the regions with the poorest satellite AOD-PM correlation (Pearson correlation coefficient (PCC) around 0.1). Our results show that the three QML products are more correlated with ground-level PMs, especially when they are paired with their corresponding PMs in terms of size: AOD with PM10, fAOD with PM2.5 and cAOD with PM coarse (R=0.41, 0.45 and 0.26, respectively). Our results show that different PM size fractions may be better predicted using different AOD size fractions, instead of total AOD. QML long-term aerosol dataset (and associated models) not only fix some problems of existing AOD data, but also provide better tools to monitor and analyse fine-mode and coarse-mode aerosols in spatial and temporal dimensions, and to further investigate their impacts on human health, climate, visibility, and biogeochemical cycling. The QML datasets can be downloaded from [ABSTRACT FROM AUTHOR]

The representations of cloud processing of gases and aerosols in some of the current state-of-the-art regional air quality models in North America and Europe are reviewed. Key processes reviewed include aerosol activation (or nucleation scavenging of aerosols), aqueous-phase chemistry, and wet deposition/removal of atmospheric tracers. It was found that models vary considerably in the parameterizations or algorithms used in representing these processes. As an emerging area of research, the current understanding of the uptake of water soluble organics by cloud droplets and the potential aqueous-phase reaction pathways leading to the atmospheric secondary organic aerosol (SOA) formation is also reviewed. Sensitivity tests using the AURAMS model have been conducted in order to assess the impact on modeled regional particulate matter (PM) from: (1) the different aerosol activation schemes, (2) the different below-cloud particle scavenging algorithms, and (3) the inclusion of cloud processing of water soluble organics as a potential pathway for the formation of atmospheric SOA. It was found that the modeled droplet number concentrations and ambient PM size distributions were strongly affected by the use of different aerosol activation schemes. The impact on the modeled average ambient PM mass concentration was found to be limited in terms of averaged PM2.5 concentration (~a few percents) but more significant in terms of PM1.0 (up to 10 percents). The modeled ambient PM was found to be moderately sensitive to the below-cloud particle scavenging algorithms, with relative differences up to 10% and 20% in terms of PM2.5 and PM10, respectively, when using the two different algorithms for the scavenging coefficient Λ) corresponding to the lower and upper bounds in the parameterization for Λ. The model simulation with the additional cloud uptake and processing of water-soluble organic gases was shown to improve the evaluation statistics for modeled PM2.5 OA compared to the IMPROVE network data, and it was demonstrated that the cloud processing of water-soluble organics can indeed be an important mechanism in addition to the traditional secondary organic gas uptake to the particle organic phase. [ABSTRACT FROM AUTHOR]

An increase in the sulfate aerosols observed in the period 1–6 April 2014 over Austria is analyzed using in situ measurements at an Austrian air quality background station, lidar measurements at the closest EARLINET stations around Austria, CAMS near-real-time data, and particle dispersion modeling using FLEXPART, a Lagrangian transport model. In situ measurements of SO2 , PM 2.5 , PM 10 , and O3 were performed at the air quality background station Pillersdorf, Austria (EMEP station AT30, 48 ∘ 43 ′ N, 15 ∘ 55 ′ E). A CAMS aerosol mixing ratio analysis for Pillersdorf and the lidar stations Leipzig, Munich, Garmisch, and Bucharest indicates the presence of an event of aerosol transport, with sulfate and dust as principal components. For the sulfate layers identified at Pillersdorf from the CAMS analysis, backward- and forward-trajectory analyses were performed, associating lidar stations with the trajectories. The lidar measurements for the period corresponding to trajectory overpass of associated stations were analyzed, obtaining the aerosol layers, the optical properties, and the aerosol types. The potential sources of transported aerosols were determined for Pillersdorf and the lidar stations using the source–receptor sensitivity computed with FLEXPART, combined with the MACCity source inventory. A comparative analysis for Pillersdorf and the trajectory-associated lidar stations showed consistent aerosol layers, optical properties and types, and potential sources. A complex pattern of contributions to sulfate over Austria was found in this paper. For the lower layers (below 2000 m) of sulfate, it was found that central Europe was the main source of sulfate. Medium to smaller contributions come from sources in eastern Europe, northwest Africa, and the eastern US. For the middle-altitude layers (between 2000 and 5000 m), sources from central Europe (northern Italy, Serbia, Hungary) contribute with similar emissions. Northwest Africa and the eastern US also have important contributions. For the high-altitude layers (above 5000 m), the main contributions come from northwest Africa, but sources from the southern and eastern US also contribute significantly. No contributions from Europe are seen for these layers. The methodology used in this paper can be used as a general tool to correlate measurements at in situ stations and EARLINET lidar stations around these in situ stations. [ABSTRACT FROM AUTHOR]

In the framework of the EURODELTA-Trends (EDT) modeling experiment, several chemical transport models (CTMs) were applied for the 1990-2010 period to investigate air quality changes in Europe as well as the capability of the models to reproduce observed long-term air quality trends. Five CTMs have provided modeled air quality data for twenty-one continuous years in Europe using emission scenarios prepared by IIASA/GAINS and corresponding year-by-year meteorology derived from ERA-interim global reanalysis. For this study, long-term observations of particle sulfate (SO42-), total nitrate (TNO3), total ammonium (TNHx) as well as sulfur dioxide (SO2) and nitrogen dioxide (NO2) for multiple sites in Europe were used to validate the model results. The trends analysis was performed for the full twenty-one years (referred to as PT), but also for two 11-year sub-periods: 1990-2000 (referred to as P1) and 2000-2010 (referred to as P2). The experiment revealed that the models were able to reproduce the faster decline in observed SO2 concentrations during the first decade, i.e. 1990-2000, with a 64-76% mean relative reduction in SO2 concentrations indicated by the EDT experiment (range of all the models) versus an 82% mean relative reduction in observed concentrations. During the second decade, P2, the models estimated a mean relative reduction in SO2 concentrations of about 34-54%, which was also in line with that observed (47%). Comparisons of observed and modeled NO2 trends revealed a mean relative decrease of 25% and between 19-23% (range of all the models) during the P1 period, and 12% and between 22-26% (range of all the models) during the P2 period, respectively. Comparisons of observed and modeled trends in SO42- concentrations during the P1 period indicated that the models were able to reproduce the observed trends at most of the sites, with a 42-54% mean relative reduction indicated by the EDT experiment (range of all models) versus a 57% mean relative reduction in observed concentrations, and with good performances also during the P2 and PT periods. Moreover, especially during the P1 period, both modeled and observational data indicated smaller reductions in SO42- concentrations compared with its gas-phase precursor (i.e. SO2), which could be mainly attributed to increased oxidant levels and pH-dependent cloud chemistry. An analysis of the trends in TNO3 concentrations indicated a 28-39% and 29% mean relative reduction in TNO3 concentrations for the full period for model data (range of all the models) and observations, respectively. Further analysis of the trends in modeled HNO3 and particle nitrate (NO3-) concentrations revealed that the relative reduction in HNO3 was larger than that for NO3- during the P1 period, which was mainly attributed to an increased availability of "free-ammonia". By contrast, trends in modeled HNO3 and NO3- concentrations were more comparable during the P2 period. Also, trends of TNHx concentrations were, in general, under-predicted by all models, with worst performance for the P1 period than for P2. Trends in modeled anthropogenic and biogenic secondary organic aerosol (ASOA and BSOA) concentrations together with the trends in available emissions of biogenic volatile organic compounds (BVOCs) were also investigated. A strong decrease in ASOA was indicated by all the models, following the reduction in anthropogenic NMVOCs precursors. Biogenic emission data provided by the modeling teams indicated a few areas with statistically significant increase in isoprene emission and monoterpene emissions during the 1990-2010 period over Fennoscandia and Eastern European regions (i.e. around 14-27%), which was mainly attributed to the increase of surface temperature. However, the modeled BSOA concentrations did not linearly follow the increase in biogenic emissions. Finally, a comprehensive evaluation against positive matrix factorization (PMF) data, available during the second period (P2) at various European sites, revealed a systematic under-estimation of the modeled SOA fractions of between a factor of 3 to 11, on average, most likely because of missing SOA precursors and formation pathways, with reduced biases for the models that accounted for chemical aging of semi-volatile SOA components in the atmosphere. [ABSTRACT FROM AUTHOR]

Ambient fine particle (PM2.5) concentrations are associated with premature mortality and other health effects. Urban populations spend a majority of their time in indoor environments, and thus exposures are modified by building envelopes. Ambient particles have been found to penetrate indoors very efficiently (penetration efficiency P≉1.0), where they are slowly removed by deposition, adsorption, and other mechanisms. Other particles are generated indoors, even in buildings with no obvious sources like combustion devices, cooking, use of aerosol products, etc.. The health effects of indoor generated particles are currently not well understood, and require information on concentrations and exposure levels.The current work apportions residential PM2.5 concentrations measured in the EXPOLIS study to ambient and non-ambient fractions. The results show that the mean infiltration efficiency of PM2.5 particles is similar in all four cities included in the analysis, ranging from 0.59 in Helsinki to 0.70 in Athens, with Basle and Prague in between. Mean residential indoor concentrations of ambient particles range from 7 (Helsinki) to 21μgm-3 (Athens). Based on PM2.5 decay rates estimated in the US, estimates of air exchange rates and indoor source strengths were calculated. The mean air exchange rate was highest in Athens and lowest in Prague. Indoor source strengths were similar in Athens, Basle and Prague, but lower in Helsinki. Some suggestions of possible determinants of indoor generated non-ETS PM2.5 were acquired using regression analysis. Building materials and other building and family characteristics were associated with the indoor generated particle levels. A significant fraction of the indoor concentrations remained unexplained. [Copyright &y& Elsevier]

This study uses a combination of data from U.K. monitoring stations and from modelling undertaken with the U.K. Meteorological Office's NAME Model to investigate the relative influences of primary and secondary particulates on total PM10 levels at sites in the United Kingdom. Co-located PM10 and sulphate aerosol measurements indicate that sulphate has a disproportionately large influence on the variation of PM10 levels in comparison to its contribution to their total mass. Comparisons of measured PM10 at urban centre, roadside and rural sites suggest that local primary sources have very little influence on daily mean levels. NAME has been used to model both primary particles and sulphate aerosol from sources across the whole of Europe. The discrepancies between modelled and observed PM10 suggest that coarse particles, such as windblown dust and resuspended roaddust, may comprise a very large, if not dominant, proportion of observed PM10 levels. The apparently minor role of primary particles (especially locally-sourced ones) raises a number of issues regarding the suitability of current U.K. and European legislation to addressing the particle problem. [ABSTRACT FROM AUTHOR]

There is considerable academic interest in the potential for air quality improvement as a co-benefit of climate change mitigation. Few studies use regional air quality models for simulating future co-benefits, but many use global chemistry-climate model output. Using regional atmospheric chemistry could provide a better representation of air quality changes than global chemistry-climate models, especially by improving the representation of elevated urban concentrations. We use a detailed regional atmospheric chemistry model (WRF-Chem v 4.2) to model European air quality in 2050 compared to 2014 following three climate change mitigation scenarios. We represent different climate futures by using air pollutant emissions and chemical boundary conditions (from CESM2-WACCM output) for three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0; a high, medium and low mitigation pathway). We find that in 2050, following SSP1-2.6, mean population-weighted PM2.5 concentrations across European countries reduces by 52 % compared to 2014. Whilst under SSP2-4.5, this average reduction is 34 %. The smallest average reduction was 18 % by following SSP3-7.0. Maximum 6-monthly-mean daily-maximum 8 h (6mDM8h) ozone (O3) is reduced across Europe by 15 % following SSP1-2.6, and 3 % following SSP2-4.5, but increases by 13 % following SSP3-7.0. This demonstrates clear co-benefits of climate mitigation. The additional resolution allows us to analyse regional differences and identify key sectors. We find that mitigation of agricultural emissions will be key for attaining meaningful co-benefits of mitigation policies, evidenced by the importance of changes in NO3 aerosol mass to determining future PM2.5 air quality and changes in CH4 emissions to future O3 air quality. [ABSTRACT FROM AUTHOR]

This study introduces a new chemistry option in the Weather Research and Forecasting model data assimilation (WRFDA) system, coupled with the WRF‐Chem model (Version 4.4.1), to incorporate aqueous chemistry (AQCHEM) in the assimilation of ground‐level chemical measurements. The new DA capability includes the integration of aqueous‐phase aerosols from the Regional Atmospheric Chemistry Mechanism (RACM) gas chemistry, the Modal Aerosol Dynamics Model for Europe (MADE) aerosol chemistry, and the Volatility Basis Set (VBS) for secondary organic aerosol production. The RACM‐MADE‐VBS‐AQCHEM scheme facilitates aerosol‐cloud‐precipitation interactions by activating aerosol particles in cloud water during the model simulation. With the goal of enhancing air quality forecasting in cloudy conditions, this new implementation is demonstrated in the weakly coupled three‐dimensional variational data assimilation (3D‐Var) system through regional air quality cycling over East Asia. Surface particulate matter (PM) concentrations and four gas species (SO2, NO2, O3, and CO) are assimilated every 6 hr for the month of March 2019. The results show that including aqueous‐phase aerosols in both the analysis and forecast can represent aerosol wet removal processes associated with cloud development and rainfall production. During a pollution event with high cloud cover, simulations without aerosols defined in cloud water exhibit significantly higher values for liquid water path, and surface PM10 (PM2.5) concentrations are overestimated by a factor of 10 (3) when wet scavenging processes dominate. On the contrary, AQCHEM proves to be helpful in simulating the wet deposition of aerosols, accurately predicting the evolution of surface PM concentrations without such overestimation. Plain Language Summary: Major air pollution events over the Korean peninsula are often observed in association with significant cloud cover, especially over the Yellow Sea to the west of the peninsula. Cloudy conditions pose challenges for both remote sensing observations and model predictions, but the inclusion of aqueous‐phase (or cloud‐borne) aerosols in the WRF‐Chem/Weather Research and Forecasting model data assimilation system improves the simulation of aerosol wet scavenging, leading to improved predictions of surface particulate matter concentrations that were otherwise substantially overestimated. Key Points: The Weather Research and Forecasting (WRF)‐Chem/WRF model data assimilation 3D‐Var system (V4.4.1) is extended for chemical data assimilation with aqueous chemistry using the Regional Atmospheric Chemistry Mechanism‐Modal Aerosol Dynamics Model for Europe‐Volatility Basis Set schemeSurface PM2.5, PM10, SO2, NO2, O3, and CO concentrations are assimilated in the coupled systemThe inclusion of aqueous‐phase aerosols in air quality cycling enhances the simulation of aerosol wet deposition in cloudy conditions [ABSTRACT FROM AUTHOR]

Air pollution has become a global issue due to rapid urbanization and industrialization. Bad air quality is Europe's most significant environmental health risk, causing serious health problems. External air pollution is not the only issue; internal air pollution is just as severe and can also lead to adverse health outcomes. IoT is a practical approach for monitoring and publishing real-time air quality information. Numerous IoT-based air quality monitoring systems have been proposed using micro-sensors for data collection. These systems are designed for outdoor air quality monitoring. They use sensors to measure air quality parameters such as C O 2 , C O , P M 10 , N O 2 , temperature, and humidity. The data are acquired with a set of sensors placed on an electric car. They are then sent to the server. Users can subscribe to the list and receive information about local pollution. This system allows real-time localized air quality monitoring and sending data to customers. The work additionally presents a secure data transmission protocol ensuring system security. This protocol provides system-wide attack resiliency and interception, which is what existing solutions do not offer. [ABSTRACT FROM AUTHOR]

The present work describes the implementation of the state of the art Cloud- J v7.3 photolysis rate calculation code in the EMEP MSC-W chemistry-transport model. Cloud- J calculates photolysis rates and accounts for cloud and aerosol optical properties at model run time, replacing the old system based on tabulated values. The performance of Cloud- J is evaluated against aerial photolysis rate observations made over the Pacific Ocean and against surface observations from three measurement sites in Europe. Numerical experiments are performed to investigate the sensitivity of the calculated photolysis rates to the spatial and temporal model resolution, input meteorology model, simulated ozone column, and cloud effect parameterization. These experiments indicate that the calculated photolysis rates are most sensitive to the choice of input meteorology model and cloud effect parameterization while also showing that surface ozone photolysis rates can vary by up to 20 % due to daily variations in total ozone column. Further analysis investigates the impact of Cloud- J on the oxidizing capacity of the troposphere, aerosol–photolysis interactions, and surface air quality predictions. Results find that the annual mean mass-weighted tropospheric hydroxyl concentration is increased by 26 %, while the photolytic impact of aerosols is mostly limited to large tropical biomass-burning regions. Overall, Cloud- J represents a major improvement over the tabulated system, leading to improved model performance for predicting carbon monoxide and daily maximum ozone surface concentrations. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a multi-pollutant sensitivity study of an air quality model over Europe with a focus on aerosols. Following the evaluation presented in the companion paper, the aim here is to study the sensitivity of the model to input data, mathematical parameterizations and numerical approximations. To that end, 30 configurations are derived from a reference configuration of the model by changing one input data set, one parameterization or one numerical approximation at a time. Each of these configurations is compared to the same reference simulation over two time periods of the year 2001, one in summer and one in winter. The sensitivity of the model to the different configurations is evaluated through a statistical comparison between the simulation results and through comparisons to available measurements. The species studied are ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), ammonia (NH3), coarse and fine aerosol particles (PM c and PM2.5), sulfate, nitrate, ammonium, chloride and sodium. For all species, the modeled concentrations are very sensitive to the parameterization used for vertical turbulent diffusion and to the number of vertical levels. For the other configurations considered in this work, the sensitivity of the modeled concentration to configuration choice varies with the species and the period of the year. O3 is impacted by options related to boundary conditions. PM c is sensitive to sea-salt related options, to options influencing deposition and to options related to mass transfer between gas and particulate phases. PM2.5 is sensitive to a larger number of options than PM c : sea-salt, boundary conditions, heterogeneous reactions, aqueous chemistry and gas/particle mass transfer. NO2 is strongly influenced by heterogeneous reactions. Nitrate shows the highest variability of all species studied. As with NO2, nitrate is strongly sensitive to heterogeneous reactions but also to mass transfer, thermodynamic related options, aqueous chemistry and computation of the wet particle diameter. While SO2 is mostly sensitive to aqueous chemistry, sulfate is also sensitive to boundary conditions and, to a lesser extent, to heterogeneous reactions. As with nitrate, ammonium is largely impacted by the different configuration choices, although the sensitivity is slightly lower than for nitrate. NH3 is sensitive to aqueous chemistry, mass transfer and heterogeneous reactions. Chloride and sodium are impacted by sea-salt related options, by options influencing deposition and by options concerning the aqueous-phase module. [Copyright &y& Elsevier]

Many studies have shown strong associations between particulate matter (PM) levels and a variety of health outcomes, leading to changes in air quality standards in many regions, especially the United States and Europe. Kuwait, a desert country located on the Persian Gulf, has a large petroleum industry with associated industrial and urban land uses. It was marked by environmental destruction from the 1990 Iraqi invasion and subsequent oil fires. A detailed particle characterization study was conducted over 12 months in 2004-2005 at three sites simultaneously with an additional 6 months at one of the sites. Two sites were in urban areas (central and southern) and one in a remote desert location (northern). This paper reports the concentrations of particles less than 10 μm in diameter (PM10) and fine PM (PM2.5), as well as fine particle nitrate, sulfate, elemental carbon (EC), organic carbon (OC), and elements measured at the three sites. Mean annual concentrations for PM10 ranged from 66 to 93 μg/m3 across the three sites, exceeding the World Health Organization (WHO) air quality guidelines for PM10 of 20 μg/m3. The arithmetic mean PM2.5 concentrations varied from 38 and 37 μg/m3 at the central and southern sites, respectively, to 31 μg/m3 at the northern site. All sites had mean PM2.5 concentrations more than double the U.S. National Ambient Air Quality Standard (NAAQS) for PM2.5. Coarse particles comprised 50-60% of PM10. The high levels of PM10 and large fraction of coarse particles comprising PM10 are partially explained by the resuspension of dust and soil from the desert crust. However, EC, OC, and most of the elements were significantly higher at the urbanized sites, compared with the more remote northern site, indicating significant pollutant contributions from local mobile and stationary sources. The particulate levels in this study are high enough to generate substantial health impacts and present opportunities for improving public health by reducing airborne PM. [ABSTRACT FROM AUTHOR]

Abstract: The PM2.5, PMcoarse and black smoke (BS) particle metrics broadly reflect different source contributions to PM10. The aim of this study was to generate data for PM2.5 at an urban background site in the UK, and to use the daily collocated measurement of PM2.5, PM10 (and hence PMcoarse) and BS to yield insight into source influences on particulate matter for input to developing PM air quality policy. Mean daily PM10, PM2.5 and BS for a year of measurement in Edinburgh were 15.5, 8.5 and 6.6μgm−3. The PM2.5 data were well-within possible future limit values proposed by the European Commission Clean Air For Europe programme. Daily PM2.5 and PM10 were significantly correlated () with PM2.5 contributing 54%, on average, to PM10. The daily BS:PM10 and BS:PM2.5 ratios were more variable, and significantly lower in summer than in winter, reflecting the greater contribution of non-black photochemical secondary particles to PM10 in summer. Analysis with respect to wind showed a dominant influence of dispersion on BS and PM2.5 but both dispersion and a wind-driven suspension influence on PMcoarse. The latter was higher than in central England (averaging about one-third of the PMcoarse), and greater for on-shore wind direction, suggesting a sea-salt source for this component in addition to other particle resuspension contributions. Overall, the data showed that excursions in PM10 were driven more by variations in PM2.5 than by PMcoarse or BS. Both PM2.5 and its proportion to PM10 were significantly elevated for air-masses passing over continental Europe and the British Isles, whereas BS varied less with air-mass origin, supporting the conclusion that concentrations of particulate matter, particularly of finer PM, are strongly influenced by regional scale synoptic meteorology (presumed to be predominantly secondary PM), whereas BS is dominated more by local sources. Comparison of BS with a nearby rural site suggested that approximately three-quarters, on average, of the urban BS was local in origin. [Copyright &y& Elsevier]

Studies on three continents have reported associations between various measures of airborne particles and daily deaths. Sulfur dioxide has also been associated with daily deaths, particularly in Europe. Questions remain about the shape of those associations, particularly whether there are thresholds at low levels. We examined the association of daily concentrations of black smoke and SO[sub2] with daily deaths in eight Spanish cities (Barcelona, Bilbao, Castellón, Gijón, Oviedo, Valencia, Vitoria, and Zaragoza) with different climates and different environmental and social characteristics. We used nonparametric smoothing to estimate the shape of the concentration — response curve in each city and combined those results using a metasmoothing technique developed by Schwartz and Zanobetti. We extended their method to incorporate random variance components. Black smoke had a nearly linear association with daily deaths, with no evidence of a threshold. A 10 µg/m³ increase in black smoke was associated with a 0.88% increase in daily deaths (95% confidence interval, 0.56%-1.20%). SO[sub2] had a less plausible association: Daily deaths increased at very low concentrations, but leveled off and then decreased at higher concentrations. These findings held in both one- and two-pollutant models and held whether we optimized our weather and seasonal model in each city or used the same smoothing parameters in each city. We conclude that the association with particle levels is more convincing than for SO[sub2], and without a threshold. Linear models provide an adequate estimation of the effect of paniculate air pollution on mortality at low to moderate concentrations. Key words: air pollution, daily mortality, dose — response relationships, hierarchical models, paniculate matter. Environ Health Perspect 109:1001-1006 (2001). [Online 25 September 2001] http://ehpnetl.niehs.nih.gov/docs/2001/109pl001-1006schwartz/a bstract.html [ABSTRACT FROM AUTHOR]

Renewable biomass plays a crucial role in transitioning toward climate-friendly heating sources; however, not without its collateral damage in terms of the disproportionately high effects on local air quality. The associated proliferation of residential heating appliances around the world, including developed regions like Europe, where an estimated 70 million are housed, does not appear to be abating. Here, we identify super self-concentrating ambient pollution events whereby solid-fuel residential heating haze is infused with a hitherto unaccounted for firelighter smoke that contributes additional adsorbing black carbon. This black carbon-organic aerosol combination results in a strong positive radiative forcing (up to 149 W m−2) and alters the boundary layer thermodynamics sufficiently so as to further suppress pollutant dilution and dispersion leading to extraordinary high submicron particulate matter (PM1: 166 µg m−3). Unfortunately, there is no silver lining in this cloud until the promotion of solid biomass fires with firelighters for ignition is replaced by a co-benefit policy. [ABSTRACT FROM AUTHOR]

Excess reactive nitrogen (Nr), including nitrogen oxides (NOx) and ammonia (NH3), contributes strongly to fine particulate matter (PM2.5) air pollution in Europe, posing challenges to public health. Designing cost-effective Nr control roadmaps for PM2.5 mitigation requires considering both mitigation efficiencies and implementation costs. Here we identify optimal Nr control pathways for Europe by integrating emission estimations, air quality modeling, exposure-mortality modeling, Nr control experiments and cost data. We find that phasing out Nr emissions would reduce PM2.5 by 2.3 ± 1.2 μg·m−3 in Europe, helping many locations achieve the World Health Organization (WHO) guidelines and reducing PM2.5-related premature deaths by almost 100 thousand in 2015. Low-ambition NH3 controls have similar PM2.5 mitigation efficiencies as NOx in Eastern Europe, but are less effective in Western Europe until reductions exceed 40%. The efficiency for NH3 controls increases at high-ambition reductions while NOx slightly decreases. When costs are considered, strategies for both regions uniformly shift in favor of NH3 controls, as NH3 controls up to 50% remain 5-11 times more cost-effective than NOx per unit PM2.5 reduction, emphasizing the priority of NH3 control policies for Europe. Reactive nitrogen (Nr) contributes strongly to PM2.5 air pollution in Europe. Here, authors identify diverse Nr control pathways for Europe depending on emission and pollution formation and a priority of NH3 control when costs are considered. [ABSTRACT FROM AUTHOR]

Ship engine combustion emits several atmospheric pollutants, such as PM, SOx, and NOx, which can have adverse health effects and are significant contributors to decreased air quality. Due to the distribution of maritime transport activity routes in the EU, a large portion of the population is exposed to shipping emissions throughout Europe. Therefore, in light of the European Commission long-term objective of "zero-waste, zero-emission" for maritime transport, the focus of this study was to quantify the impact of shipping emissions in the present, as well as the future, considering both emissions projection for the shipping sector and a climate change scenario. The WRF-CHIMERE modelling system was used to quantify the impact of shipping in Europe. To obtain the current and future contributions of maritime transport to the total pollutant concentrations, simulations were divided into two present (baseline and without shipping) and three future scenarios (shipping projection, climate change, and shipping projection and climate change). The results indicate that the current and future impacts of shipping emissions on pollutant concentrations are similar in some regions (NO2 for Northern Europe and SO2 for Southern Europe), which is due to the enforcement of emission control areas for those pollutants. However, efforts towards lowering emissions from the shipping sector are negated in the south of this domain due to the concentration changes caused by the climate change scenario. In light of these changes, the introduction of a NECA is proposed for the Mediterranean, which would help us to make great strides to reduce the impact of the shipping sector in the region and aid in counteracting the effects of climate change. [ABSTRACT FROM AUTHOR]

The article offers information on the air quality in Europe. Topics discussed include precursor gases of air pollution such as ozone, secondary nitrogen dioxide and secondary particulate matter; emissions in agriculture, commercial, institutional and households, and energy production; and emissions from gasoline engines with direct injection.

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]

Particle mass concentration is the most important particle metric for air quality. Ambient threshold values for PM2.5 and PM10 have been established in Europe (EU Air Quality Directive 2008/50/EC) and worldwide. However, to date no reference aerosol exists for calibrating commercial PM-measuring instruments. As a result, comparisons with the reference gravimetric method need to take place in the field at least twice a year at 2 different sites. These procedures are time-consuming, expensive and suffer from high measurement uncertainties. METAS is currently validating a novel facility to generate a homogeneous mixture of different aerosol types (salt, dust, soot and aged soot) in a downward pipe flow. The ultimate goal is to generate synthetic ambient aerosols in the laboratory for the calibration of PM measuring instruments. This facility consists of a 2.3-m-long pipe with inner diameter of 160 mm. The primary aerosols are injected in the center of the pipe and are subsequently mixed by three air jets arranged concentrically around the pipe. Details on the design of the facility will be presented in the talk. Isokinetic sampling can be achieved by using differently sized extraction cones that lead the aerosol to the reference gravimetric method and the different devices under test (oscillating microbalances, light scattering instruments etc.). Measurements of the homogeneity of an aerosol consisting of 500 nm PSL particles showed that 2.3 m downstream of the aerosol injection the distribution was homogeneous within 5% and that the flow exhibited a turbulent "flat" velocity profile at the sampling location.The flow field has been modeled by the COMSOL CFD module by taking advantage of the symmetry of the geometry so that only 1/3 of it had to be meshed. Since the Reynolds number of the flow is around 1800, turbulence had to be taken into account. Comparisons of the CFD results with measured velocity profiles using Laser Doppler velocimetry showed that a low-Reynolds number k-epsilon model that resolves the flow up to the wall (no wall functions) was appropriate to simulate the velocity characteristics of the pipe flow.Currently, measurements are being performed by mixing salt and dust aerosols, whereas in a second step fresh and (photo-chemically) aged soot will be added in order to simulate better the physicochemical properties of atmospheric aerosols. Preliminary results of these investigations will be presented at the conference. [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]

It is well known that ship emissions contribute significantly to atmospheric pollution. However, the impact on air quality can regionally vary, as influenced by parameters such as the composition of the regional shipping fleet, state of background atmospheric pollution, and meteorological aspects. This study compared two regions with high shipping densities in 2015. These include the North and Baltic Seas in Europe and the Yellow and East China Seas in China. Here, a key focal point is an evaluation of differences and similarities of the impacts of ship emissions under different environmental conditions, particularly between regions with medium (Europe) and high air pollution (China). To assess this, two similarly performed chemical transport model runs were carried out with highly resolved bottom-up ship emission inventories for northern Europe and China, calculated with the recently developed MoSES model, publicly available emissions data for nonshipping sources (EDGAR, MEIC). The performance of the model was evaluated against measurement data recorded at coastal stations. Annual averages at affected coastal regions for NO 2 , SO 2 , O 3 and PM 2.5 were modeled in Europe to be 3, below 0.3 , 2.5 , 1 and in China 3, 2, 2–8, 1.5 , respectively, all given in μ g / m 3 . In highly affected regions, such as large harbors, the contributions of ship-related emissions modeled in Europe were 15%, 0.3 %, − 12.5 %, 1.25 % and in China were 15%, 6%, − 7.5 %, 2%, respectively. Absolute pollutant concentrations from ships were modeled slightly higher in China than in Europe, albeit the relative impact was smaller in China due to higher emissions from other sectors. The different climate zones of China and the higher level of atmospheric pollution were found to seasonally alter the chemical transformation processes of ship emissions. Especially in northern China, high PM concentrations during winter were found to regionally inhibit the transformation of ship exhausts to secondary PM, and reduce the impact of ship-related aerosols, compared to Europe. [ABSTRACT FROM AUTHOR]

We conduct the first 4D‐Var inversion of NH3 accounting for NH3 bi‐directional flux, using CrIS satellite NH3 observations over Europe in 2016. We find posterior NH3 emissions peak more in springtime than prior emissions at continental to national scales, and annually they are generally smaller than the prior emissions over central Europe, but larger over most of the rest of Europe. Annual posterior anthropogenic NH3 emissions for 25 European Union members (EU25) are 25% higher than the prior emissions and very close (<2% difference) to other inventories. Our posterior annual anthropogenic emissions for EU25, the UK, the Netherlands, and Switzerland are generally 10%–20% smaller than when treating NH3 fluxes as uni‐directional emissions, while the monthly regional difference can be up to 34% (Switzerland in July). Compared to monthly mean in‐situ observations, our posterior NH3 emissions from both schemes generally improve the magnitude and seasonality of simulated surface NH3 and bulk NHx wet deposition throughout most of Europe, whereas evaluation against hourly measurements at a background site shows the bi‐directional scheme better captures observed diurnal variability of surface NH3. This contrast highlights the need for accurately simulating diurnal variability of NH3 in assimilation of sun‐synchronous observations and also the potential value of future geostationary satellite observations. Overall, our top‐down ammonia emissions can help to examine the effectiveness of air pollution control policies to facilitate future air pollution management, as well as helping us understand the uncertainty in top‐down NH3 emissions estimates associated with treatment of NH3 surface exchange. Plain Language Summary: Atmospheric ammonia contributes to air pollutants and excessive deposition of reactive nitrogen that is detrimental to sensitive ecosystems. Ammonia is emitted mainly by agricultural livestock and fertilizer use. While surface measurements of NH3 are sparse, satellite observations can provide near daily global coverage. Here we calculate monthly NH3 emissions over Europe, the only region adopting NH3 control policies, using an air quality model coupled with a process‐based bi‐directional NH3 flux scheme and NH3 measurements observed by the CrIS satellite instrument. Our CrIS‐derived annual regional total anthropogenic NH3 emissions are close (<2% difference) to statistic‐based bottom‐up estimates and are 10%–20% lower than when treating NH3 exchange between the atmosphere and biosphere as one‐way emissions. Our top‐down NH3 emissions estimates may help to assess the efficacy of NH3 abatement policies and provide quantitative support for future policy making. Key Points: First 4D‐Var inversion to include bi‐directional flux of NH3, based on CrIS NH3 and cross‐validated with surface observationsBi‐directional flux reduces posterior regional NH3 emissions by 10%–20% annually (monthly up to 34%), compared to uni‐directional emissionsPosterior NH3 emissions generally improve simulated seasonality and magnitude of NH3 and NHx wet deposition [ABSTRACT FROM AUTHOR]

The past 60 years have seen large reductions in vehicle emissions of particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HCs), sulfur dioxide (SO2), and lead (Pb). Advanced emission after-treatment technologies have been developed for gasoline and diesel vehicles to meet increasingly stringent regulations, yielding absolute emission reductions from the on-road fleet despite increased vehicle miles traveled. As a result of reduced emissions from vehicles and other sources, the air quality in cities across the U.S. and Europe has improved greatly. Turn-over of the on-road fleet, increasingly stringent emission regulations (such as Tier 3 in the U.S., LEV III in California, Euro 6 in Europe, and upcoming rules in these same regions), and the large-scale introduction of electric vehicles will lead to even lower vehicle emissions and further improvements in air quality. We review historical vehicle emissions and air quality trends and discuss the future outlook. [ABSTRACT FROM AUTHOR]

Exposure to air pollution, especially from particulate matter, is generally accepted to be one of the most important public health problems in Europe and worldwide. The effects caused in the general population are associated with relatively small relative risks, but if the ubiquity of exposure is considered, the attributable number of events is large. Furthermore, there is evidence that the effects in sensitive population subgroups (such as the elderly, those with chronic diseases and children) are stronger. Within large European Union funded collaborative projects (such as the Air Pollution and Health: a European Approach - APHEA), effect modification by geographical characteristics has been investigated and it was found that in warmer countries, in locations where particles come from traffic and where the proportion of the elderly is greater, particle toxicity is increased. These characteristics are particularly relevant to Southern European locations. From other projects we know that meteorological, climatic, environmental and socioeconomic factors are effect modifiers of the effects of specific air pollutants. In this presentation we will show the evidence on the short-term health effects of particulate and gaseous air pollutants and emphasize particularly results concerning southern Europe and potential effect modifiers. The gaps in knowledge and the need to study air pollution in Southern European countries more extensively will be demonstrated. To conduct useful research, good quality air pollution and health data are needed. [ABSTRACT FROM AUTHOR]

Abstract: Coarse particles of aerodynamic diameter between 2.5 and 10 μm (PMc) are produced by a range of natural (windblown dust and sea sprays) and anthropogenic processes (non-exhaust vehicle emissions, industrial, agriculture, construction and quarrying activities). Although current ambient air quality regulations focus on PM2.5 and PM10, coarse particles are of interest from a public health point of view as they have been associated with certain mortality and morbidity outcomes. In this paper, an analysis of coarse particle levels in three European capitals (London, Madrid and Athens) is presented and discussed. For all three cities we analysed data from both traffic and urban background monitoring sites. The results showed that the levels of coarse particles present significant seasonal, weekly and daily variability. Their wind driven and non-wind driven resuspension as well as their roadside increment due to traffic were estimated. Both the local meteorological conditions and the air mass history indicating long-range atmospheric transport of particles of natural origin are significant parameters that influence the levels of coarse particles in the three cities especially during episodic events. [Copyright &y& Elsevier]

Nowadays, high-time resolved aerosol studies are mandatory to better understand atmospheric processes, such as formation, removal, transport, deposition or chemical reactions. This work focuses on PM10 physical and chemical characterisation with high-time resolution: elements (from Na to Pb), ions and OC/EC fractions concentration were determined during two weeks in summer and two in winter 2006 with 4-hours resolution. Further measurements aimed at hourly elemental characterisation of fine and coarse fractions and at the determination of particles number concentration in the 0.25–32 μm size range in 31 bins. The chemical mass closure was carried out in both seasons, enhancing intra-day differences in PM10 composition. In Milan, the highest contribution came from organic matter (34% and 33% in summer and winter, respectively); other important contributors were secondary inorganic compounds (16% and 24% in summer and winter, respectively) and, in summer, crustal matter (14%). Temporal trends showed strong variations in PM10 composition during contiguous time-slots and diurnal variations in different components contribution were identified. Moreover, peculiar phenomena, which would have hardly been detected with 24-hours samplings, were evidenced. Particles removal due to precipitations, aerosol local production and long range transport were studied in detail. [ABSTRACT FROM AUTHOR]

Abstract: The significance of the heterogeneous formation of particulate nitrate, rarely included in chemistry-transport models (CTMs), is investigated. According to several field campaigns, particulate nitrate in a coarse particle (2–10μm) can be obtained by reaction of nitric acid with calcium and magnesium carbonates. This process significantly contributes to the total nitrate mass concentration over land, particularly in summer. We introduce this heterogeneous reaction in the CHIMERE CTM and analyze its impact on total nitrate, nitric acid and aerosol particles, by statistical comparison of one-year long simulations with EMEP measurements over Europe. Several values of the nitric acid uptake coefficient are tested in order to investigate the sensitivity to this parameter, and we propose an optimal value for our study. The model performance in simulating nitrates and PM10 significantly improves when the heterogeneous nitrate formation is included. This process also greatly improves the simulation of coarse nitrate by comparison with field campaign measurements near Paris city. [Copyright &y& Elsevier]

Urban areas are hot spots of intense emissions, and they influence air quality not only locally but on a regional or even global scale. The impact of urban emissions over different scales depends on the dilution and chemical transformation of the urban plumes which are governed by the local- and regional-scale meteorological conditions. These are influenced by the presence of urbanized land surface via the so-called urban canopy meteorological forcing (UCMF). In this study, we investigate for selected central European cities (Berlin, Budapest, Munich, Prague, Vienna and Warsaw) how the urban emission impact (UEI) is modulated by the UCMF for present-day climate conditions (2015–2016) using two regional climate models, the regional climate models RegCM and Weather Research and Forecasting model coupled with Chemistry (WRF-Chem; its meteorological part), and two chemistry transport models, Comprehensive Air Quality Model with Extensions (CAMx) coupled to either RegCM and WRF and the "chemical" component of WRF-Chem. The UCMF was calculated by replacing the urbanized surface by a rural one, while the UEI was estimated by removing all anthropogenic emissions from the selected cities. We analyzed the urban-emission-induced changes in near-surface concentrations of NO2 , O3 and PM 2.5. We found increases in NO2 and PM 2.5 concentrations over cities by 4–6 ppbv and 4–6 µgm-3 , respectively, meaning that about 40 %–60 % and 20 %–40 % of urban concentrations of NO2 and PM 2.5 are caused by local emissions, and the rest is the result of emissions from the surrounding rural areas. We showed that if UCMF is included, the UEI of these pollutants is about 40 %–60 % smaller, or in other words, the urban emission impact is overestimated if urban canopy effects are not taken into account. In case of ozone, models due to UEI usually predict decreases of around -2 to -4 ppbv (about 10 %–20 %), which is again smaller if UCMF is considered (by about 60 %). We further showed that the impact on extreme (95th percentile) air pollution is much stronger, and the modulation of UEI is also larger for such situations. Finally, we evaluated the contribution of the urbanization-induced modifications of vertical eddy diffusion to the modulation of UEI and found that it alone is able to explain the modeled decrease in the urban emission impact if the effects of UCMF are considered. In summary, our results showed that the meteorological changes resulting from urbanization have to be included in regional model studies if they intend to quantify the regional footprint of urban emissions. Ignoring these meteorological changes can lead to the strong overestimation of UEI. [ABSTRACT FROM AUTHOR]

In the first part, this work reports that during the global "anthropopause" period, that was imposed in March and April 2020 for limiting the spread of COVID-19, the concentrations of basic air pollutants over Europe were reduced by up to 70%. During May and June, the gradual lift of the stringent measures resulted in the recovery of these reductions with pollution concentrations approaching the levels before the lockdown by the end of June 2020. In the second part, this work examines the alleged correlations between the reported cases of COVID-19 and temperature, humidity and particulate matter for March and April 2020 in Europe. It was found that decreasing temperatures and relative humidity with increasing concentrations of particulate matter are correlated with an increase in the number of reported cases during these 2 months. However, when these calculations were repeated for May and June, we found a remarkable drop in the significance of the correlations which leads us to question the generally accepted inverse relation between pandemics and air temperature at least during the warmer months. Such a relationship could not be supported in our study for SARS-CoV-2 virus and the question remains open. In the third and last part of this work, we examine the question referring to the origin of pandemics. In this context we have examined the hypothesis that the observed climate warming in Siberia and the Arctic and the thawing of permafrost could result to the release of trapped in the permafrost pathogens in the atmosphere. We find that although such relations cannot be directly justified, they present a possible horrifying mechanism for the origin of viruses in the future during the developing global warming of our planet in the decades to come. Overall the findings of our study indicate that: (1) the reduction of anthropogenic emissions in Europe during the "anthropopause" period of March and April 2020 was significant, but when the lockdown measures were raised the concentrations of atmospheric pollutants quickly recovered to pre-pandemic levels and therefore any possible climatic feedbacks were negligible; (2) no robust relationship between atmospheric parameters and the spread of COVID-19 cases can be justified in the warmer part of the year and (3) more research needs to be done regarding the possible links between climate change and the release of new pathogens from thawing of permafrost areas. [ABSTRACT FROM AUTHOR]

Air pollution is one of the main causes of damages to human health in Europe, with an estimate of about 380 000 premature deaths per year in the EU28, as the result of exposure to fine particulate matter (PM 2.5) only. In this work, we focus on one specific region in Europe, the Po basin, a region where chemical regimes are the most complex, showing important non-linear processes, especially those related to interactions between NO x and NH 3. We analyse the sensitivity of PM 2.5 concentration to NO x and NH 3 emissions by means of a set of EMEP model simulations performed with different levels of emission reductions, from 25 % up to a total switch-off of those emissions. Both single and combined precursor reduction scenarios are applied to determine the most efficient emission reduction strategies and quantify the interactions between NO x and NH 3 emission reductions. The results confirmed the peculiarity of secondary PM 2.5 formation in the Po basin, characterised by contrasting chemical regimes within distances of a few (hundred) kilometres, as well as non-linear responses to emission reductions during wintertime. One of the striking results is the slight increase in the PM 2.5 concentration levels when NO x emission reductions are applied in NO x -rich areas, such as the surroundings of Bergamo. The increased oxidative capacity of the atmosphere is the cause of the increase in PM 2.5 induced by a reduction in NO x emission. This process could have contributed to the absence of a significant PM 2.5 concentration decrease during the COVID-19 lockdowns in many European cities. It is important to account for this process when designing air quality plans, since it could well lead to transitionary increases in PM 2.5 at some locations in winter as NO x emission reduction measures are gradually implemented. While PM 2.5 chemical regimes, determined by the relative importance of the NO x vs. NH 3 responses to emission reductions, show large variations seasonally and spatially, they are not very sensitive to moderate (up to 50 %–60 %) emission reductions. Beyond 25 % emission reduction strength, responses of PM2.5 concentrations to NO x emission reductions become non-linear in certain areas of the Po basin mainly during wintertime. [ABSTRACT FROM AUTHOR]

Résumé: Cet article présente une analyse de l'impact sur la qualité de l'air des mesures de confinement généralisées à toute l'Europe pendant près de deux mois au printemps 2020, pour faire face à la crise sanitaire de la Covid-19. Ces mesures ont abouti à une réduction drastique et inédite des émissions d'oxydes d'azote, principalement émis par le trafic routier. De nombreuses études ont été menées par plusieurs équipes européennes avec le même objectif, mais les méthodes d'analyse peuvent différer. Dans le cas présent, deux approches basées sur la mise en œuvre du modèle de chimie-Transport CHIMERE sont appliquées à l'échelle de la France et de l'Europe. L'une repose sur l'exploitation de simulations de la qualité de l'air dans lesquelles les données de mesures des réseaux de surveillance in situ sont assimilées pour coller au mieux à l'observation. L'autre interprète des scénarios de réduction d'émissions représentatifs des mesures de confinement. Les avantages et inconvénients de chacune sont commentés. Elles aboutissent cependant à des conclusions cohérentes entre elles, et avec la plupart des études recensées sur le sujet : le confinement fut logiquement à l'origine d'une forte baisse des concentrations de dioxyde d'azote (jusqu'à 60 %) dans toutes les grandes villes européennes et ces travaux permettent d'appréhender une limite supérieure de ces niveaux qu'il sera difficile d'abaisser. En revanche, les niveaux de particules influencés par d'autres sources que le trafic routier et par des phénomènes physico-chimiques complexes ont diminué dans une moindre mesure et selon une dynamique différente, l'effet du confinement ayant été ressenti avec quelques jours de décalage. Ces résultats constituent une source de réflexion essentielle pour les décideurs en charge de la définition de politiques publiques pour la qualité de l'air. This article presents an analysis of the impact on air quality of lockdown measures implemented throughout Europe for nearly two months in spring 2020 to combat the Covid-19 health crisis. These measures have resulted in a drastic and unprecedented reduction in nitrogen dioxide emissions, mainly emitted by road traffic. Several European teams have conducted studies with the same objective, but with possibly different methods. Here, we applied two approaches based on the implementation of the CHIMERE chemistry-transport model to France and to Europe. One is based on the use of air quality simulations in which measurement data from in-situ monitoring networks are adjusted to correspond closely to observations. The other interprets emission reduction scenarios typical of lockdown measures. The advantages and disadvantages of each are discussed. However, they lead to conclusions that are consistent with each other, and with most of the studies identified on the subject: lockdown naturally decreased nitrogen dioxide concentrations by up to 60% in all large European cities. These studies make it possible to set an upper limit of these levels which will be difficult to lower. On the other hand, the levels of particulate matter, which is influenced by sources other than road traffic and by complex physicochemical phenomena, decreased less and followed a different curve, as the lockdown effect was felt a few days later. These results provide essential insights for decision-makers designing public policies for air quality. [ABSTRACT FROM AUTHOR]

Increasing evidence from experimental studies suggests that the losses of semi-volatile vapors to chamber walls could be responsible for the underestimation of organic aerosol (OA) in air quality models that use parameters obtained from chamber experiments. In this study, a box model with a volatility basis set (VBS) scheme was developed, and the secondary organic aerosol (SOA) yields with vapor wall loss correction were optimized by a genetic algorithm based on advanced chamber experimental data for biomass burning. The vapor wall loss correction increases the SOA yields by a factor of 1.9–4.9 and leads to better agreement with measured OA for 14 chamber experiments under different temperatures and emission loads. To investigate the influence of vapor wall loss correction on regional OA simulations, the optimized parameterizations (SOA yields, emissions of intermediate-volatility organic compounds from biomass burning, and enthalpy of vaporization) were implemented in the regional air quality model CAMx (Comprehensive Air Quality Model with extensions). The model results from the VBS schemes with standard (VBS_BASE) and vapor-wall-loss-corrected parameters (VBS_WLS), as well as the traditional two-product approach, were compared and evaluated by OA measurements from five Aerodyne aerosol chemical speciation monitor (ACSM) or aerosol mass spectrometer (AMS) stations in the winter of 2011. An additional reference scenario, VBS_noWLS, was also developed using the same parameterization as VBS_WLS except for the SOA yields, which were optimized by assuming there is no vapor wall loss. The VBS_WLS generally shows the best performance for predicting OA among all OA schemes and reduces the mean fractional bias from -72.9 % (VBS_BASE) to -1.6 % for the winter OA. In Europe, the VBS_WLS produces the highest domain average OA in winter (2.3 µgm-3), which is 106.6 % and 26.2 % higher than VBS_BASE and VBS_noWLS, respectively. Compared to VBS_noWLS, VBS_WLS leads to an increase in SOA by up to ∼80 % (in the Balkans). VBS_WLS also leads to better agreement between the modeled SOA fraction in OA (fSOA) and the estimated values in the literature. The substantial influence of vapor wall loss correction on modeled OA in Europe highlights the importance of further improvements in parameterizations based on laboratory studies for a wider range of chamber conditions and field observations with higher spatial and temporal coverage. [ABSTRACT FROM AUTHOR]