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Concentration fluctuations from continuous small sources in a neutral boundary layer were investigated by mean of high-resolution Large Eddy Simulation (LES). The data set includes concentration moments up to the fourth order and shows the range of validity of the Gamma probability density function (PDF) model for the concentration fluctuations and the transition to a Gaussian PDF for ground sources. We also investigated systematically the off-center line peaks in the concentration variance showing that they are persistent for ground level sources while they disappear according to theoretical arguments for elevated sources. The analysis includes a thorough investigation of the distribution of the most energetic components in the frequency domain by using spectral analysis of the LES results and a stochastic model based on simple theoretical arguments. This analysis supports the picture that the peak in concentration variance frequency distribution is related to both the plume dispersion geometry and the turbulent flow. The results also confirm the recent literature findings that for an elevated source the peak in the concentration variance frequency distribution is almost independent from the crosswind location for a given downwind distance from the source. To our knowledge no previous LES or wind tunnel study had the completeness of the current study.

The exacerbation of the urban heat island due to global warming poses a serious risk to the health of citizens. Furthermore, the alteration of the urban microclimate affects air quality with an expected increase in the concentrations of harmful pollutants. Greening cities is an effective tool to mitigate these effects. However, the effect of tree planting in urban street canyons is still a debated topic. Despite their positive effect on temperature and their filtering action, trees can hinder air circulation thus limiting pollutant removal processes. In this context, it is essential to understand and model the effect of trees on the ventilation of street pollutants, heat and moisture . To this end, we present in this work the results of an experimental campaign conducted in a wind tunnel. An urban geometry with a street canyon perpendicular to the wind direction was reproduced. A linear source of passive scalar simulated the emission of pollutants from vehicular traffic. Reduced scale trees have been conceived to mimic a realistic aerodynamic behaviour. We investigated four different configurations of vegetation density: a street with no trees, two trees in the middle of the street, two rows of scattered trees and two dense rows of trees. Concentration and velocity measurements were performed in order to characterize the transfer processes of pollutants inside the street and to estimate a bulk vertical exchange rate. Results show that the presence of trees alters the concentration field in the street with a progressive shift from a nearly two-dimensional to a three-dimensional field. Despite the significant spatial variation in concentration, the presence of trees does not alter the overall efficiency of the ventilation as the vertical bulk exchange velocity remains almost constant in the different configurations. The statistical analysis of the turbulent concentration signal gives other insights in the transfer processes. The turbulent signal measured in different positions of the cavity and for different tree density follows a Gamma distribution with constant fluctuation intensity suggesting an almost universal behaviour within the canyon and providing a powerful modelling tool. Finally, combined measurements of concentration and velocity allows to measure the turbulent mass fluxes at the roof height and investigate their spectrum therefore enlightening the effect of trees on typical scales of motion.

Air pollution is a dramatic issue that grips the majority of densely populated cities in the world. It is nowadays quite evident that there is a relationship between air quality and some types of cancers (i.e. lung and bladder cancer), as reported by the International Agency for Research on Cancer (IARC 2012). Although the time spent commuting usually represents a small portion of a person's daily time (3-6%), it is responsible around for 21% of daily personal exposure and roughly 30% of the total inhaled dose (Dons et al. 2012). To gain information on this topic, we conducted an air quality measurement campaign (six weeks between November and December 2021) on three different routes within the metropolitan city of Lyon (France). These routes were chosen to be representative of different urban areas (e.g. city centre, periphery, vegetated areas). The measurements were taken two times for day (i.e. in the morning and the evening, in order to simulate the commuters round trip) using four different modes (walk, bike, car and public transport). Two different portable air quality sensors were used to measure the pollutants: the MONICA sensors (developed by ENEA, De Vito et al. 2021) that measure PM1, PM2.5, PM10, NO2, CO and O3 and the AirBeam 2 sensors (provided by ATMO AURA) that measure only the particular matters. The objective of this study is twofold: from one side to assess the exposure choosing different modes of commuting and, from the other side, to evaluate how the influence of the meteorological-climatic variables (e.i. temperature, relative humidity, precipitation, wind direction, wind speed, cloud cover, solar radiation and atmospheric boundary layer stability/instability) affect the air quality. Preliminary results show that private car users are generally affected by lower levels of air pollution with respect to the other modes (as expected, Okokon et al. 2017), but this is strongly influenced by the type of ventilation used (internal or external air recirculation, open and closed windows). ReferenceDe Vito, S., Esposito, E., Massera, E., Formisano, F., Fattoruso, G., Ferlito, S., ... & Di Francia, G. (2021). Crowdsensing IoT Architecture for Pervasive Air Quality and Exposome Monitoring: Design, Development, Calibration, and Long-Term Validation. Sensors, 21(15), 5219.Dons, E., Panis, L. I., Van Poppel, M., Theunis, J., & Wets, G. (2012). Personal exposure to black carbon in transport microenvironments. Atmospheric Environment, 55, 392-398.IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. (2012). Chemical agents and related occupations. IARC monographs on the evaluation of carcinogenic risks to humans, 100, 9–562.Okokon, E. O., Yli-Tuomi, T., Turunen, A. W., Taimisto, P., Pennanen, A., Vouitsis, I., ... & Lanki, T. (2017). Particulates and noise exposure during bicycle, bus and car commuting: A study in three European cities. Environmental Research, 154, 181-189.

We propose a new experimental protocol to investigate the atmospheric dispersion of a dense gas in wind-tunnel experiments. Simultaneous measurements of concentration and velocity are performed by coupling a flame ionisation detector (FID) and a hot-wire anemometer (HWA), whose probes are located sufficiently close to each other so that the respective measurements correspond to a same sampling volume. The heavy gas emission consists in a mixture of air, carbon dioxide, and ethane. Carbon dioxide is used as a buoyant agent, and ethane is used as a tracer, its concentration being detected by the FID. In this context, the main metrological issue of the setup concerns the response of the FID and the HWA to different proportions of the two gases in the mixture. Notably, the presence of carbon dioxide affects the linear response of the FID, which can attain a saturation level, as well as the response of the HWA, due to the varying density of the gas. This can be compensated by determining a non-linear calibration curve of the FID, which is used to determine the instantaneous fluid density, and to apply a time-dependent correction to the HWA response. To analyse the performances of the coupled HWA–FID system we realised wind-tunnel experiments of tracer dispersion in a turbulent boundary layer. The estimate of mass fluxes through different sections downwind the source enlightens the reliability of the experimental results, and show that the measurements within a negatively buoyant gas plume are as accurate as those within a passive scalar plume.

Greening cities is a key solution to improve the urban microclimate and mitigate the impact of climate change. However, the effect of tree planting on pollutant dispersion in streets is still a debated topic. To shed light on this issue, we present a wind-tunnel experiment aimed at investigating the effect of trees on street canyon ventilation. An idealized urban district was simulated by an array of blocks, and two rows of model trees were arranged at the sides of a street canyon oriented perpendicularly with respect to the wind direction. Reduced scale trees were chosen to mimic a realistic shape and aerodynamic behaviour. Three different spacings between the trees were considered. A passive scalar was injected from a line source placed at ground level and concentration measurements were performed in the whole canyon. Results show that the presence of trees alters the concentration pattern in the street with a progressive shift from a nearly two-dimensional to a three-dimensional field depending on tree density. Despite the significant change of the concentration field induced by trees, the average level of pollution in the street, and thus the overall ventilation efficiency, does not show a specific trend with the density of trees.

Through a unified mathematical framework, the stochastic behavior of three celebrated low-order lumped models, previously proposed for paleoclimate simulations, is considered. Due to the coherence resonance mechanism, the feedbacks between noise and the dynamical system reproduce the hallmark of the Pleistocene climate, i.e. the 100 ky pulsation, in a range of the model parameters that is unexpectedly wide and far from the original modeling setting. In this way, the issue of arbitrary coefficient tuning of lumped approaches in paleoclimatology can be partially bypassed. A stability analysis of the considered dynamical systems allowed the parameter space to be exploited, in order to separate the deterministic-dominated region from the stochastic-dominated region. Noise intensity is varied and the closeness in the parameter space to Hopf bifurcations and/or bistable conditions is investigated in order to understand what conditions make the models prone to coherence resonance with a 100-ky pulsation, with or without the forcing induced by varying astronomical parameters.

Air pollution in cities, especially in existing urban canyons, poses a global significant long-term health risk to the urban population, and urban planners are faced with the challenge of increasing the transport of pollutants out of cities. In recent years, many research and review articles have explored passive methods of altering the urban canyon geometry using ‘obstacles’ that alter the dispersion of air flow in these canyons, thereby enhancing pollutant dispersion. These obstacles have been categorised (in previous review articles) into porous and non-porous barriers. Porous barriers include vegetated shrubs and trees, while non-porous barriers include parked cars, low boundary walls, roadside barriers, wind catchers and solar chimneys. This paper expands on previous reviews to highlight newer studies, their findings, and challenges in implementing these measures for existing urban canyons. In addition, it attempts to bring us one step closer to developing urban design guidelines that improve air quality in the urban environment.

Nitrogen dioxide (NO

Purpose Molecular and cellular studies reported a role of cadmium in risk of advanced breast cancer (BC). However epidemiological evidence is limited. Our previous study suggests that cadmium might be related to a decreased risk of ER- and ER-PR- breast tumors. In this study, we further explored the association between long-term exposure to airborne cadmium and risk of BC by stage, grade of differentiation, and histological types at diagnosis. Methods A nested case-control study of 4,401 cases and 4,401 matched controls was conducted within the French E3N cohort. A Geographic Information System (GIS) based metric was employed to evaluate outdoor airborne exposure to cadmium. Multivariable adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated using conditional logistic regression models. Results There was no statistically significant association between cadmium exposure and stage of BC in the multivariable analyses. The adjusted ORs for the fifth versus first quintile were 1.02 (95% CI: 0.83–1.25), 1.11 (95% CI: 0.84–1.49), and 0.67 (95% CI: 0.37–1.24) for stages I, II, and III-IV BC, respectively. The subgroup analyses showed no statistically significant association between cadmium exposure and grade of differentiation of BC at diagnosis. However, further analyses by histological type suggested a positive dose-response association between cadmium and risk of invasive tubular carcinoma (ITC) BC (OR for the fifth versus first quintile = 3.44 (95% CI: 1.10–10.7)). Conclusions Our results do not support the hypothesis that airborne cadmium exposure may have a role in advanced BC risk, but suggest that cadmium may be associated with an increased risk of ITC. However, these results should be considered with caution, and more epidemiological studies are needed to confirm our findings and to improve our understanding of the effects of cadmium exposure according to several clinic-pathological characteristics of BC.

Non-Gaussian statistics of large-scale fields are routinely observed in data from atmospheric and oceanic campaigns and global models. Recent direct numerical simulations (DNSs) showed that large-scale intermittency in stably stratified flows is due to the emergence of sporadic, extreme events in the form of bursts in the vertical velocity and the temperature. This phenomenon results from the interplay between waves and turbulent motions, affecting mixing. We provide evidence of the enhancement of the classical small-scale (or internal) intermittency due to the emergence of large-scale drafts, connecting large- and small-scale bursts. To this aim we analyze a large set of DNSs of the stably stratified Boussinesq equations over a wide range of values of the Froude number ($Fr\approx 0.01-1$). The variation of the buoyancy field kurtosis with $Fr$ is similar to (though with smaller values than) the kurtosis of the vertical velocity, both showing a non-monotonic trend. We present a mechanism for the generation of extreme vertical drafts and vorticity enhancements which follows from the exact equations for field gradients., Comment: 7 pages, 4 figures

The objective of this research project was the design and development of an integrated model for odor emission estimation in wastewater treatment plants. The SMAT's plant, the largest wastewater treatment facility in Italy, was used as a case study. This article reports the results of the characterization phase that led to the definition and design of the proposed conceptual model for odor emission estimation. In this phase, concentrations of odor chemical tracers (VOC, H2S, NH3) and odor concentrations were monitored repeatedly. VOC screening with GC-MS analysis was also performed. VOC concentrations showed significant variability in space and magnitude. NH3 and H2S were also detected at considerable concentrations. Results were elaborated to define a spatially variable linear relationship between the sum of odor activity values (SOAV) and odor concentrations. Based on the results, a conceptual operational model was presented and discussed. The proposed system is composed by a network of continuous measurement stations, a set of algorithms for data elaboration and synchronization, and emission dispersion modeling with the application of Lagrangian atmospheric models.

Dioxins, are persistent organic pollutants with endocrine disrupting properties and are classified as human carcinogens. To better characterise historical atmospheric dioxin exposure in epidemiological studies, we performed a comprehensive inventory of dioxin-emitting sources between 1990 and 2008, in France, at a fine spatial resolution, according to the methodology of the United Nations Environment Program (UNEP) Toolkit. Overall, we identified 2620 distinct dioxin-emitting sources over the French territory. The majority of the sources were geolocated either at the stack (43%) or at the building (27%). The final database contains the technical characteristics and activity rates for each source over the study period. These data served to estimate total annual dioxin emissions (g-TEQ/year). We compared our estimates with both measurements and emissions inventories (at departmental and national level). The discrepancies in the comparisons between the Toolkit estimates, the dioxin measurements available, and inventories remained within the uncertainty range of the UNEP Toolkit estimates. The differences observed were due to a general lack of data and to the large number of small incinerators with large dioxin emissions inventoried. Due to better access to relevant data and a decrease in emissions, the UNEP Toolkit estimates get closer to measurements and estimates of others inventories for more recent years. We created the first database containing the annual atmospheric dioxin emissions for a large number of emission sources at the facility scale for an entire country. This database was used to assess exposure to dioxins in epidemiological studies.

Background: Dioxins, Group 1 carcinogens, are emitted by industrial chlorinated combustion processes and suspected to increase breast cancer risk through receptor-mediated pathways. Objectives: We estimated breast cancer risk associated with airborne dioxin exposure, using geographic information system (GIS) methods and historical exposure data. Methods: We designed a case-control study (429 breast cancer cases diagnosed between 1990 and 2008, matched to 716 controls) nested within the E3N (Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale) cohort. Airborne dioxin exposure was assessed using a GIS-based metric including participants' residential history, technical characteristics of 222 dioxin sources, residential proximity to dioxin sources, exposure duration and wind direction. Odds ratios (OR) and 95% confidence intervals (CI) associated with quintiles of cumulative exposure were estimated using multivariate logistic regression models. Results: We observed no increased risk of breast cancer for higher dioxin exposure levels overall and according to hormone-receptor status. We however observed a statistically significant OR for Q2 versus Q1 overall (1.612, 95% CI: 1.042–2.493) and for estrogen-receptor (ER) positive breast cancer (1.843, 95% CI: 1.033–3.292). Conclusions: Overall, as well as according to hormone-receptor status, no increased risk was observed for higher airborne dioxin exposure. The increased risk for low exposure levels might be compatible with non-monotonic dose-response relationship. Confirmation of our findings is required. Our GIS-based metric may provide an alternative in absence of ambient dioxin monitoring and may allow assessing exposure to other pollutants. Keywords: Breast cancer, Endocrine disruptors, Dioxins, Geographic information system, Tumor receptor

We investigate the dynamics of turbulent dispersion by means of direct numerical simulations of a passive tracer released in a homogeneous isotropic turbulent flow. We focus on the link between the probability density function (PDF) of the passive scalar concentration and its mixing properties. In particular, we show how the gamma distribution can be used as a suitable model for the PDF, as has been previously verified in wind tunnel experiments in wall-bounded turbulent flows. Finally, we develop a simple mixing model to estimate the time scale that regulates the decay rate of the intensity of concentration fluctuations.

Under crosswind conditions, road cyclists experience an extra drag force and a destabilising lateral force. In these conditions a group of cyclists manages to reorganise its spatial formation to minimise these forces forming an echelon, i.e a diagonal single pace line of riders staggered across the road, a configuration which is markedly different from those adopted in wind-free conditions. To study the effect of the crosswind on drag and lateral forces on the riders we performed wind-tunnel experiments using a scale model cyclist and measuring the forces by means of a load cell. Several configurations with one, two, and four cyclists have been investigated varying yaw angles. Results show that, in a basic 4 rider configuration at a 50 $$^{\circ }$$ ∘ yaw angle, a sheltered rider within the echelon experiences less than 30% of the drag of the guttered rider behind the echelon, struggling against the crosswind. Furthermore, we show that an echelon is worth being adopted under crosswind conditions only beyond a 30 $$^{\circ }$$ ∘ yaw angle. At this critical 30 $$^{\circ }$$ ∘ yaw angle the drag on the guttered rider doubles when the gap to the front group increases from 10 cm to 1 m (in real scale). These results can be of interest in defining road cycling race strategies and they allow some significant configurations to be identified and further investigated in more complex experiments.

An assessment of the impact of cruise ship emissions while hotelling in the port of Naples has been studied by means of wind tunnel and computational fluid dynamics (CFD) models. An area of about 1.2 km2 was reproduced at a scale of 1:500 for the wind tunnel experiments. The worst but most emission scenario with three cruise ships emitting at the same time was studied. Wind blows from the south-east with a speed of 3 m/s at funnel height in neutral stability conditions of the atmospheric boundary layer. Two different values of the velocity ratio UR = 1 and UR = 4 (funnel gas velocity/wind speed) were considered. In the experiments, Ethane was used as the tracer gas and the concentration was measured at 35 receptor points inside the urban structure and at different heights. Experimental data show good agreement with those estimated by numerically solving steady Reynolds-Averaged Navier-Stokes (RANS) with the k-ω shear-stress transport (SST) turbulence model. The results were used to analyse the accuracy of the predictions of the model CALifornia Puff (CALPUFF), testing two model options: the building downwash module and the parameterisation of the dispersion coefficients. The CALPUFF results are less accurate than the CFD simulations and show a general tendency to underestimate the experimental data. The optimization process improves the performance of CALPUFF. Finally, a more comprehensive analysis of the effect of a varying UR in the range 0.25–16 was undertaken using numerical models. The research provides useful insights to improve the assessment of the impact of ship emissions in port cities.

International audience; We analyse the metrological aspect related to systems devoted to the simultaneous measurements of (one point) velocity and scalar concentration statistics. We consider systems based on the coupling of an anemometer (Laser Doppler or Hot Wire) with a Flame Ionization Detector. In particular, we focus on the estimate of the cross-correlation velocity-concentration. Key aspects in the reliability of such measurements are related to the identification of an optimal distance between the two probes, the time lag with which the velocity and concentration signals are acquired, and, eventually , the influence of seeding particles (when using a Laser Doppler Anemometer) on the concentration measurements. We investigate these aspects by performing wind-tunnel experiments on the scalar dispersion down wind a ground-level source in a turbulent boundary layer. This analysis allowed us to identify a time delay and a convenient distance between the signals provided by the anemometer and the concentration detector. Results also show that the seeding used for the Laser Doppler Anemometer measurements modifies the cutoff frequency in the concentration spectra and induces a slightly larger uncertainty on the statistics of scalar field. The results show the reliability of both systems in estimating (horizontal and vertical) turbulent mass fluxes.

Background Although the genetic and hormonal risk factors of breast cancer are well identified, they cannot fully explain the occurrence of all cases. Epidemiological and experimental studies have suggested that exposure to environmental pollutants, especially those with potential estrogenic properties, as polychlorinated biphenyls (PCBs) may have a role in breast cancer development. Being the most abundantly detected in human tissues and in the environment, congener 153 (PCB153) is widely used in epidemiological studies as indicator for total PCBs exposure. Objectives We aimed to estimate the association between cumulative atmospheric exposure to PCB153 and breast cancer risk. Methods We conducted a case-control study of 5222 cases and 5222 matched controls nested within the French E3N cohort from 1990 to 2011. Annual atmospheric PCB153 concentrations were simulated with the deterministic chemistry-transport model (CHIMERE) and were assigned to women using their geocoded residential history. Their cumulative PCB153 exposure was calculated for each woman from their cohort inclusion to their index date. Breast cancer odds ratios (ORs) associated with cumulative PCB153 exposure and their 95% confidence intervals (95% CIs) were estimated using multivariate conditional logistic regression models. Results Overall, our results showed a statistically significant linear increase in breast cancer risk related to cumulative atmospheric exposure to PCB153 as a continuous variable (adjusted OR = 1.19; 95% CI: 1.08–1.31, for an increment of one standard deviation among controls (55 pg/m3)). Among women who became postmenopausal during follow-up, the association remained statistically significant (adjusted OR = 1.23; 95% CI: 1.09–1.39). In analyses by hormone receptors status, the positive association remained significant only for ER-positive breast cancer (adjusted OR = 1.18; 95% CI: 1.05–1.33). Discussion This study is the first to have estimated the impact of atmospheric exposure to PCB153 on breast cancer risk. Our results showed a statistically significant increase in breast cancer risk, which may be limited to ER-positive breast cancer. These results warrant confirmation in further independent studies but raise the possibility that exposure to PCB153 increase breast cancer risk.

The dispersion of airborne pollutants in the urban atmosphere is a complex, canopy-driven process. The intricate structure of the city, the high number of potential sources, and the large spatial domain make it difficult to predict dispersion patterns, to simulate a great number of scenarios, and to identify the high-impact emission areas. Here we show that these complex transport dynamics can be efficiently characterized by adopting a complex network approach. The urban canopy layer is represented as a complex network. Street canyons and their intersections shape the spatial structure of the network. The direction and the transport capacity of the flow in the streets define the direction and the weight of the links. Within this perspective, pollutant contamination from a source is modeled as a spreading process on a network, and the most dangerous areas in a city are identified as the best spreading nodes. To this aim, we derive a centrality metric tailored to mass transport in flow networks. By means of the proposed approach, vulnerability maps of cities are rapidly depicted, revealing the nontrivial relation between urban topology, transport capacity of the street canyons, and forcing of the external wind. The network formalism provides promising insight in the comprehensive analysis of the fragility of cities to air pollution.

The dispersion dynamics of a contaminant released in the atmosphere is crucial for risk assessments and environmental analyses. Yet, because of the unsolved problem of turbulence, analytical solutions physically-derived are currently limited to the Gaussian models for the mean concentration field. In this work, we have obtained simple solutions for the concentration statistics of a passive scalar released from a punctual source. The main result is a novel analytical solution for the passive scalar variance, which is obtained from the contaminant transport equation. We have verified this solution against wind-tunnel data, and further adopted it in a simple stochastic model to provide closed relationships for the temporal statistics of concentration (e.g., the mean duration and occurrence of the peak events). These results may serve as a rapid and practical way to estimate the intensity and duration of the concentration fluctuations of a pollutant released in the atmosphere.

Understanding the dynamics of mass and heat exchange between a street canyon and the overlying atmosphere is crucial to predict air quality and microclimatic conditions within dense urban areas. Previous studies have demonstrated that the bulk transfer between the street and the overlying flow is entirely governed by the intensity of turbulent fluctuations within the street. The aim of this experimental study is to evaluate how the geometry of the street canyon and the solar radiation on building façades influence the turbulent velocity field within a two-dimensional street canyon and thus the global street canyon ventilation. The study was carried in a wind tunnel. The boundary conditions inside the canyon were modified by heating its windward and leeward walls and by changing the cavity aspect-ratio. The flow field in a cross-section of the street canyon was measured with particle image velocimetry. Temperatures were measured by means of thermocouples. The velocity and vorticity fields are analysed and discussed.

Identifying the long-term effects of airborne pollutants requires the computation of the spatial and temporal variability of their concentration in air to estimate the exposure of the population. To estimate exposure levels of individuals in a breast cancer case control study nested in a national prospective cohort, we determine here the differential impact of a variety of cadmium and dioxin sources on urban air over a large urban area and over a period of almost 20years. To that end, we couple an emission model, to estimate dioxin and cadmium atmospheric annual releases, with an urban dispersion model in order to compute pollutant concentration fields at a fine temporal (1h) and spatial (25m) resolution. The reliability of the modelling chain is compared to two types of measurement: i) localized industrial emissions and ii) dioxin and cadmium air monitoring data (from 2007 to 2008), collected at a fixed station, placed in the city centre, as well as at three mobile short-term dioxin monitoring stations, located in the suburbs (the latter providing dioxin data, only). Comparisons between measured and estimated emissions show non-negligible difference, with a correlations for dioxin (rs=0.42) and cadmium (rs=0.41). Despite this, mean values between estimated emissions and emission measurements are close to each other, in particular for cadmium. Weekly average modelled concentrations show an overall good agreement with weekly average measured concentrations in spring and summer but are generally lower than monitored data in winter due to peak concentrations from diffuse sources representing an important proportion of emissions in 2007/2008. The model provides better results for cadmium than for dioxin. Despite the relevant errors in the model predictions, the model meets the validation criteria, defined by Chang and Hanna for an urban dispersion model. Simulation scenarios of air pollutant concentrations, reconstructed over the last 20years, show the effects of the variability of the pollutant sources over time with decreasing levels of dioxin and cadmium concentrations in air. This is primarily due to the reduction in localized industrial releases, which results in a general trend of homogenization of the exposure of the population. The model further allows us to dissociate the contribution of different types of pollutant sources on the population exposure. The impact on local concentrations due to industrial emissions, which were originally responsible for the major impact on air quality, is shown to drop over the years by 99% and 92% for dioxin and cadmium, respectively. Today, the major contributions are due to diffuse miscellaneous sources in the case of dioxin and to traffic-related emissions for cadmium. Average modelled concentrations at the study subjects' residential locations range from 10.2 to 82.1fg-TEQ/m3 for dioxin and 0.10 to 1.6ng/m3 for cadmium and are comparable with data from the literature. The study results will be essential to increase the accuracy of the assessment of long-term airborne dioxin and cadmium exposure and improve the results of epidemiological studies.

We review the efforts made by the scientific community in more than seventy years to elucidate the behaviour of concentration fluctuations arising from localized atmospheric releases of dynamically passive and non-reactive scalars. Concentration fluctuations are relevant in many fields including the evaluation of toxicity, flammability, and odour nuisance. Characterizing concentration fluctuations requires not just the mean concentration but also at least the variance of the concentration in the location of interest. However, for most purposes the characterization of the concentration fluctuations requires knowledge of the concentration probability density function (PDF) in the point of interest and even the time evolution of the concentration. We firstly review the experimental works made both in the field and in the laboratory, and cover both point sources and line sources. Regarding modelling approaches, we cover analytical, semi-analytical, and numerical methods. For clarity of presentation we subdivide the models in two groups, models linked to a transport equation, which usually require a numerical resolution, and models mainly based on phenomenological aspects of dispersion, often providing analytical or semi-analytical relations. The former group includes: large-eddy simulations, Reynolds-averaged Navier–Stokes methods, two-particle Lagrangian stochastic models, PDF transport equation methods, and heuristic Lagrangian single-particle methods. The latter group includes: fluctuating plume models, semi-empirical models for the concentration moments, analytical models for the concentration PDF, and concentration time-series models. We close the review with a brief discussion highlighting possible useful additions to experiments and improvements to models.

Several European urban areas are characterised by low air quality due to high local emission per unit surface. A further key feature can be related to the pollutant load due to adverse local meteo-climatic conditions. This study aims to compare the two urban agglomerations of Torino and Lyon – located on opposite sides of the Alps and characterised by similar size and population – to enlighten the role of meteorology on local pollutant dispersion. The assessment of air quality has been developed by monitoring network data, emissions analysis and the SIRANE urban dispersion model. Although the two agglomerations have similar NOX and PM10 emissions, the simulation results show higher ground level concentrations in Torino. To quantify the effect of meteorology on this excess of concentrations, we run simulations in Torino imposing the meteorological conditions of Lyon and vice versa. This implies an overall reduction of ground level concentrations in the city centre of Torino between 20% and 40% (analogously, Lyon concentrations increase by a similar amount). These results show the peculiar difficulties faced by Po valley's cities in maintaining pollution levels below regulatory thresholds and highlight the need of systemic policies and site-specific mitigation to reduce air pollution health risks.

The concentration of a passive scalar dispersed in a turbulent flow exhibits a complex stochastic dynamics. In this paper, we present a minimalist stochastic model that resembles the concentration statistics of a passive scalar emitted from a localized source in a neutral boundary layer. The model provides closed forms for the crossing rates and times — the mean frequency of exceeding a certain concentration level and the mean time above it. Three concentration statistics are needed as model inputs: the mean, the standard deviation, and the integral scale. By giving analytical relationships also for these statistics, we provide a completely closed methodology that may serve as a rapid and practical tool to estimate the dynamics of a pollutant dispersed in the atmosphere. Results are validated against wind-tunnel measurements.

Due to the overall growth of the world population and to the progressive shift from rural to urban centres, 70% of the world population is expected to live in urban areas in 2050. This trend is alarming when related to the constant decline of urban air quality at the global level. To cope with this rapid urbanization, solutions for sustainable cities are extensively sought. In this framework, the mitigation of air pollution in street canyons plays a crucial role. The street canyon (a street flanked by high buildings on both sides) is the fundamental unit of the urban tissue, as well as a vital public and residential space. Street canyons are particularly vulnerable to air pollution due to traffic emissions, low ventilation conditions, and the number of citizens exposed. Tree planting in street canyons is often used as a pollution mitigation strategy, due to the filtering effect of vegetation on airborne pollutants. However, from the aerodynamic point of view, trees can obstruct the wind flow thus reducing canyon ventilation and leading to higher pollutant concentrations. In this framework, we present the results of an experimental study aimed at evaluating how tree planting influences the flow and concentration fields within a street canyon. The study was carried out in a recirculating wind tunnel. An idealised urban district was simulated by an array of square blocks, whose orientation with respect to the incident wind was varied. Within this urban geometry, two rows of model trees were arranged at the sides of a street canyon. Three configurations with different spacing between the trees were considered. A passive scalar was injected from a line source placed at ground level to simulate traffic emissions. Concentration and flow field measurements were performed in several cross-sections of the street canyon. Results showed the effect of trees on the spatial distribution of pollutants. Moreover, a characteristic exchange velocity between the street canyon and the overlying atmosphere was estimated to quantify the overall canyon ventilation under several wind directions and different planting densities. These preliminary results provide city planners with first recommendations for the sustainable design of urban environments. Moreover, the experimental dataset is valuable in validating numerical simulations of air pollution in cities accounting for urban vegetation.

International audience; The dynamics of a passive scalar plume in a turbulent boundary layer is experimentally investigated via vertical turbulent transport time series. Experimental data are acquired in a rough-wall turbulent boundary layer that develops in a recirculating wind tunnel setup. Two source sizes in an elevated position are considered in order to investigate the influence of the emission conditions on the plume dynamics. The analysis is focused on the effects of the meandering motion and the relative dispersion of the plume with respect to its center of mass. First, classical statistics are investigated. We found that (in accordance with previous studies) the meandering motion is the main factor responsible for differences in the variance and intermittency, as well as the kurtosis and power spectral density, between the two source sizes. On the contrary, the mean and the skewness are slightly affected by the emission conditions. With the aim to characterize the temporal structure of the turbulent transport series, the visibility algorithm is exploited to carry out a complex network-based analysis. In particular, two network metrics-the average peak occurrence and the assortativity coefficient-are analyzed, as they are able to capture the temporal occurrence of extreme events and their relative intensity in the series. The effects of the meandering motion and the relative dispersion of the plume are discussed in view of the network metrics, revealing that a stronger meandering motion is associated with higher values of both the average peak occurrence and the assortativity coefficient. The network-based analysis advances the level of information of classical statistics by characterizing the impact of the emission conditions on the temporal structure of the signals in terms of extreme events (namely, peaks and pits) and their relative intensity. In this way, complex networks provide-through the evaluation of network metrics-an effective tool for time-series analysis of experimental data.

BACKGROUND Breast cancer is the most frequent cancer in women in industrialized countries. Lifestyle and environmental factors, particularly endocrine-disrupting pollutants, have been suggested to play a role in breast cancer risk. Current epidemiological studies, although not fully consistent, suggest a positive association of breast cancer risk with exposure to several International Agency for Research on Cancer Group 1 air-pollutant carcinogens, such as particulate matter, polychlorinated biphenyls (PCB), dioxins, Benzo[a]pyrene (BaP), and cadmium. However, epidemiological studies remain scarce and inconsistent. It has been proposed that the menopausal status could modify the relationship between pollutants and breast cancer and that the association varies with hormone receptor status. OBJECTIVE The XENAIR project will investigate the association of breast cancer risk (overall and by hormone receptor status) with chronic exposure to selected air pollutants, including particulate matter, nitrogen dioxide (NO2), ozone (O3), BaP, dioxins, PCB-153, and cadmium. METHODS Our research is based on a case-control study nested within the French national E3N cohort of 5222 invasive breast cancer cases identified during follow-up from 1990 to 2011, and 5222 matched controls. A questionnaire was sent to all participants to collect their lifetime residential addresses and information on indoor pollution. We will assess these exposures using complementary models of land-use regression, atmospheric dispersion, and regional chemistry-transport (CHIMERE) models, via a Geographic Information System. Associations with breast cancer risk will be modeled using conditional logistic regression models. We will also study the impact of exposure on DNA methylation and interactions with genetic polymorphisms. Appropriate statistical methods, including Bayesian modeling, principal component analysis, and cluster analysis, will be used to assess the impact of multipollutant exposure. The fraction of breast cancer cases attributable to air pollution will be estimated. RESULTS The XENAIR project will contribute to current knowledge on the health effects of air pollution and identify and understand environmental modifiable risk factors related to breast cancer risk. CONCLUSIONS The results will provide relevant evidence to governments and policy-makers to improve effective public health prevention strategies on air pollution. The XENAIR dataset can be used in future efforts to study the effects of exposure to air pollution associated with other chronic conditions. INTERNATIONAL REGISTERED REPORT DERR1-10.2196/15167

The large-eddy simulation (LES) model uDALES is used to evaluate the predictive skill of the operational air quality model SIRANE. The use of LES in this study presents a novel approach to air quality model evaluation, avoiding sources of uncertainty and providing numerical control that permits systematic analysis of targeted parametrisations and assumptions.A case study is conducted over South Kensington, London with the morphology, emissions, meteorological conditions and boundary conditions carefully matched in both models. The dispersion of both inert (NOx) and reactive (NO, NO2 and O3) pollutants under neutral, steady-state conditions is simulated for a south-westerly and westerly wind direction. A quantitative comparison between the two models is performed using statistical indices (the fractional bias, FB, the normalised mean squared error, NMSE, and the fraction in a factor of 2, FAC2).SIRANE is shown to successfully capture the dominant trends with respect to canyon-averaged concentrations of inert NOx (FB = −0.08, NMSE = 0.08 and FAC2 = 1.0). The prediction of along-canyon velocities is shown to exhibit sources of systematic error dependant on the angle of incidence of the mean wind (FB = −0.18). The assumption of photostationarity within SIRANE (deviations from equilibrium of up to 170% exist close to busy roads) is also identified as a significant source of systematic bias resulting in over- and underpredictions of NO2 (FB = −0.18) and O3 (FB = 0.14) respectively. The validity of the assumed uniform in-canyon concentration is assessed by analysing the pedestrian, leeward and windward concentrations resolved in uDALES. The use of canyon-averaged concentrations to predict pedestrian level exposure is shown to result in significant underestimations. Linear regression is used to effectively capture the relationship between pedestrian- and canyon-averaged concentrations in uDALES. Correction factors are derived (m≈1.62 and R2=0.92 for inert NOx) that are capable of significantly improving SIRANE's ability to assess pedestrian level exposure for the conditions investigated in this study. The prevalence of intersections and advective nature of the shear layer are highlighted as important differences between modelling real heterogeneous urban morphology and idealised infinite canyons. Keywords: Urban air quality, Model evaluation, Large-eddy simulation, Street canyon modelling, Traffic emissions, Pollutant dispersion