Observations of bedforms on a dissipative macrotidal beach

Field measurements of wave ripples and megaripples were made with a Sand Ripple Profiler in the surf and shoaling zones of a sandy macrotidal dissipative beach at Perranporth, UK in depths 1–6 m and significant wave heights up to 2.2 m. A frequency domain partitioning approach allowed quantification of height (η), length (λ) and migration rate of ripples and megaripples. Wave ripples with heights up to 2 cm and wavelengths ～20 cm developed in low orbital velocity conditions (u _m?<?0.65 m/s) with mobility number ψ?<?25. Wave ripple heights decreased with increasing orbital velocity and were flattened when mean currents were >0.1 m/s. Wave ripples were superimposed on top of megaripples (η?=?10 cm, λ?=?1 m) and contributed up to 35 % of the total bed roughness. Large megaripples with heights up to 30 cm and lengths 1–1.8 m developed when the orbital velocity was 0.5–0.8 m/s, corresponding to mobility numbers 25–50. Megaripple heights and wavelengths increased with orbital velocity but reduced when mean current strengths were >0.15 m/s. Wave ripple and megaripple migrations were generally onshore directed in the shoaling and surf zones. Onshore ripple migration rates increased with onshore-directed (+ve) incident wave skewness. The onshore migration rate reduced as offshore-directed mean flows (undertow) increased in strength and reached zero when the offshore-directed mean flow was >0.15 m/s. The migration pattern was therefore linked to cross-shore position relative to the surf zone, controlled by competition between onshore-directed velocity skewness and offshore-directed mean flow.     

Assessment of the Kraków inhabitants’ health risk caused by the exposure to inhalation of outdoor air contaminants

Health risk associated with the exposure to the polluted atmospheric air inhalation was estimated for the residents of Kraków, Poland. The air pollution concentration data were obtained from the air-quality monitoring system of the city in 2007–2016. The carcinogenic risk of the studied subpopulations was not acceptable under the formula of C₆H₆ > BaP > As(PM10) > Cd(PM10) > Pb(PM10) > Ni(PM10). The total carcinogenic risk (Rt) amounted to 3.04E?04 for children, 2.22E?04 for infants, 1.45E?04 for women, and 1.22E?04 for men. The same risk was calculated for the top three locations of the monitoring stations in this respect, within the city of Kraków: Kurdwanów Housing Estate, Nowa Huta district, and Krasińskiego Av. Non-carcinogenic risk in the case of all six monitoring stations and in respect of all the studied subpopulations, resulting from the exposure to PM10 and for NO₂ for all stations in case of children and infants, as well as, for adults at Krasińskiego Av. and Dietla Str. stations was rated medium. For C₆H₆ in the case of adults, children, and infants the risk was rated low. The total risk (HI) of non-carcinogenic pollution was rated medium and ranged as follows: 6.53 for children, 4.70 for infants, 3.19 for women, and 2.67 for men. That type of risk was decreasing at the station locations as follows: Krasińskiego Av. > Dietla Str. > Nowa Huta district > Kurdwanów Housing Estate > Z?oty Róg Str. > Piastów Housing Estate.     

Statistical Properties of Mine Tremor Aftershocks

Mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of South Africa. The statistical properties of mine-tremor aftershocks were investigated as part of an endeavour to assess the hazard and manage the risk. Data from two gold mines in the Carletonville mining district were used in the analysis. Main shocks were aligned in space and time and the aftershock sequences stacked and analysed. The aftershocks were found to satisfy Gutenberg–Richter scaling, with a b value close to 1. Aftershock activity diminished with time in accordance with the modified Omori law, with p values close to 1. However, the relationship between the main shock and its biggest aftershock violated Båths law, with ΔM _L ≈ 1.9 for main shocks with M _L < 3 and increasing for main shocks with M _L > 3. The aftershock density was found to fall-off with distance as r ^?1.3, suggesting triggering by dynamic stress.     

Retrospective Study on the Predictability of Pattern Informatics to the Wenchuan M8.0 and Yutian M7.3 Earthquakes

Two large earthquakes occurred in the western part of China in 2008, one of them being the Yutian (35.6°N, 81.6°E) M7.3 earthquake that occurred on March 21 (BJT) and the other the Wenchuan (31.0°N, 103.4°E) M8.0 earthquake that occurred on May 12 (BJT). In this paper, the West Continental China (included in 20.0°–50.0°N, 70.0°–110.0°E region) was the study region for verifyong the predictability of the pattern informatics (PI) method using the receiver-operating characteristic curve (ROC) test and R score test. Different forecasting maps with different calculating parameters were obtained. The calculating parameters were the grid size Δx, base time t _b, reference interval t _b to t ₁, change interval t ₁ to t ₂, and forecasting interval t ₂ to t ₃. In this paper, the base time t _b fixed to June 1, 1971, the ending forecast time t ₃ fixed to June 1, 2008, and the forecasting interval t ₂ to t ₃ changed from 1 to 10 years, and the grid sizes were chosen as 1° × 1° and 2° × 2°, respectively. The results show that the PI method could forecast the Yutian M7.3 and Wenchuan M8.0 earthquakes only using suitable parameters. Comparing the forecast results of grid sizes 1° × 1° and 2° × 2°, the models with 2° × 2° grids were better. Comparing the forecast results with different forecasting windows from 1 to 10 years, the models with forecasting windows of 4–8 years were better using the ROC test, and the models with forecasting windows of 7–10 years were better using the R score test. The forecast efficiency of the model with a grid size of 2° × 2° and forecast window of 8 years was the best one using either the ROC test or the R score test.     

Time series analysis and forecasting for air pollution in small urban area: an SARIMA and factor analysis approach

Despite the existing public and government measures for monitoring and control of air quality in Bulgaria, in many regions, including typical and most numerous small towns, air quality is not satisfactory. In this paper, factor analysis and Box–Jenkins methodology are applied to examine concentrations of primary air pollutants such as NO, NO₂, NO_x, PM10, SO₂ and ground level O₃ in the town of Blagoevgrad, Bulgaria within a 1 year period from 1st September 2011 to 31st August 2012, based on hourly measurements. By using factor analysis with PCA and Promax rotation, a high multicollinearity between the six pollutants has been detected. The pollutants were grouped in three factors and the degree of contribution of the factors to the overall pollution was determined. This was interpreted as the presence of common sources of pollution. The main part of the study involves the performance of time series analysis and the development of univariate stochastic seasonal autoregressive integrated moving average (ARIMA) models with recording on a hourly basis as seasonality. The study also incorporates the Yeo–Johnson power transformation for variance stabilizing of the data and model selection by using Bayersian information criterion. The obtained SARIMA models demonstrated very good fitting performance with regard to the observed air pollutants and short-term predictions for 72 h ahead, in particular in the case of ozone and particulate matter PM10. The presented statistical approaches allow the building of non-complex models, effective for short-term air pollution forecasting and useful for advance warning purposes in urban areas.     

Evolution of earthquake losses in Portuguese residential building stock

The evolution of the expected earthquake losses in different Portuguese regions was studied in order to determine whether the natural regeneration of buildings could contribute to the mitigation of seismic risk, although the building exposure has increased over time in most analysed regions. To achieve this goal, five inter-related risk indicators were estimated, based on the Portuguese censuses’ surveys of residential buildings and inhabitants obtained in two different moments in time: 2001 and 2011. The FEMA (2008) approach was used to estimate the risk indicators, i.e., the Annualized Economic and Human earthquake Losses, either in absolute terms or normalised by building and population exposure. This study offers a perspective of the seismic risk in the Portuguese mainland, provides a comparison of risk levels between different epochs, and analyses the obtained results in order to compare the risk among Portuguese regions. It is important to mention that the comparison of economic losses based on the building stocks surveyed in 2001 and in 2011 took into account the Portuguese inflation rate in that time interval. The main findings of the study show that the natural regeneration of the residential housing stock contributes to the reduction of the expected seismic economic losses in Portugal, at an average rate of 14 % per 10 years, and to the reduction of the expected annualized human losses to almost one half after 10 years. The results support the conclusion that the natural regeneration of the residential housing stock contributed to the mitigation of the seismic risk in mainland Portugal, in the 10 year period under analysis, even though there was an increase of the building exposure in the region.     

Bather density as a predominant factor for health effects related to recreational bathing: results from the Greek bathers cohort study

Our aim was to examine the health effects on bathers from exposure to recreational seawater on three beaches with different microbiology quality and bather density through a cohort study. An initial questionnaire and a 10 day follow up were used. Univariate and backward logistic regression analyses were used to asses the risk of developing symptoms or diseases among the bathers. In total, 3805 bathers were included in the study and 149 samples were collected from the three beaches. Despite all the beaches being characterized of high quality the levels of bacterial indicators differed among them. Health effects among bathers were not associated with bacterial indicators. A statistically significant increased risk for symptoms related to respiratory illness, gastroenteritis, medical consultation and use of medication was observed among bathers at the higher bather density beaches. Beach bather numbers should always be taken into account when considering a risk assessment approach.     

Indoor activity size distribution of the short-lived radon progeny

Activity size distribution of the short-lived radon progeny in indoor air was measured continuously over several weeks. Two different measurement techniques were used: a direct measurement with a low-pressure Berner cascade impactor for attached fraction of ²¹⁴Pb and ²¹⁴Bi (≥100 nm) and an indirect determination based on measurement with a wire screen diffusion battery (unattached fraction 0.5–5 nm, ²¹⁸Po, ²¹⁴Pb). In parallel, the meteorological parameters like temperature, humidity were registered. Measured activity size distribution of radon progeny can be approximated by a sum of three log-normal distributions modes (nucleation, accumulation and coarse). The greatest activity fraction was adsorbed on aerosol particles in the accumulation size range (100–1000 nm) with activity median aerodynamic diameters (AMAD_a) and geometric standard deviations (GSD _a ) values of 250–500 nm, and 1.5–3.5, respectively. The influence of the weather conditions on the activity of the accumulation particles was not significant. In contrast to the results of measurements a small but significant fraction of the radon progeny (average value 5 %) was attached to coarse particles (>1000 nm). This fraction varied between 0 and 10 %. On the other hand, although the amount of unattached activities not more 10 % of the total activity, but is considered to yield about 50 % of the total radiation dose. The mean thermodynamic equivalent diameters of ²¹⁸Po and ²¹⁴Pb were determined to be 1.28 and 1.30 nm with relative mean geometric standard deviations of 1.30 and 1.24, respectively. Based on the obtained results of radon progeny size distributions (attached and unattached), the total deposition fractions of the human lung were evaluated by using a lung deposition model.     

Application of an optical disdrometer to characterize simulated rainfall and measure drop-size distribution

ABSTRACT

Knowledge of rainfall characteristics such as drop-size distribution is essential for the development of erosion-mitigation strategies and models. This research used an optical disdrometer to elucidate the relationships between raindrop-size distribution, median volume drop diameter (D₅₀), kinetic energy and radar reflectivity (dBz) of simulated rainfall of different intensities. The D₅₀ values were higher for the simulated rain than for natural rain at almost all rainfall intensities, perhaps due to variations in rainfall types and the turbulence in natural rain that breaks up large drops. The kinetic energy ranged from 26.67 to 5955.51 J m^?2 h ^?1, while the median volume drop diameter (D₅₀) was in the range 1.94–7.25 mm, for intensities between 1.5 and 202.6 mm h^?1. The relationship between radar reflectivity (Z) and the intensity (R) of the simulated rain was best described by a power law function (Z = aR^b), with a and b coefficients in the ranges 162–706 and 0.94–2.46, respectively, throughout the range of rainfall intensities (1.5–202.6 mm h^?1).     

Nonlinear dynamics and recurrence analysis of extreme precipitation for observed and general circulation model generated climates

A statistical framework based on nonlinear dynamics theory and recurrence quantification analysis of dynamical systems is proposed to quantitatively identify the temporal characteristics of extreme (maximum) daily precipitation series. The methodology focuses on both observed and general circulation model (GCM) generated climates for present (1961–2000) and future (2061–2100) periods which correspond to 1xCO₂ and 2xCO₂ simulations. The daily precipitation has been modelled as a stochastic process coupled with atmospheric circulation. An automated and objective classification of daily circulation patterns (CPs) based on optimized fuzzy rules was used to classify both observed CPs and ECHAM4 GCM‐generated CPs for 1xCO₂ and 2xCO₂ climate simulations (scenarios). The coupled model ‘CP‐precipitation’ was suitable for precipitation downscaling. The overall methodology was applied to the medium‐sized mountainous Mesochora catchment in Central‐Western Greece. Results reveal substantial differences between the observed maximum daily precipitation statistical patterns and those produced by the two climate scenarios. A variable nonlinear deterministic behaviour characterizes all climate scenarios examined. Transitions’ patterns differ in terms of duration and intensity. The 2xCO₂ scenario contains the strongest transitions highlighting an unusual shift between floods and droughts. The implications of the results to the predictability of the phenomenon are also discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Discrimination test between the Halphen (A and B) and the gamma distributions

Hydrological frequency analysis is the most widely used method to estimate risk for extreme values. The most used statistical distributions to fit extreme value data in hydrology can be regrouped in three classes: class C of regularly varying distributions, class D of sub exponential and class E, Exponential depending on their tail behavior. The Halphen distributions (Halphen type A (HA), Halphen type B (HB)) are separated by the Gamma distribution; these three distributions belong to class D and can be displayed in the (δ₁, δ₂) moment-ratio diagram. In this study, a statistical test for discriminating between HA, HB and the Gamma distribution is developed. The methodology is based on: (1) the generation of N samples of different sizes n around the Gamma curve; (2) the determination of the confidence zones around the Gamma curve for each fixed couple (δ₁, δ₂) moment-ratios and finally; (3) the study of the power of the test developed and the calculation of the type 2 error β and the power of the test which is 1-β for a fixed significance level α. Results showed that the test is powerful especially for high coefficients of skewness. This test will be included in Decision Support System of the HYFRAN-PLUS software.     

The 21 May 2003 Tsunami in the Western Mediterranean Sea: Statistical and Wavelet Analyses

We report the statistical and wavelet analyses of the 21 May 2003 tsunami produced by an M _w 6.8–6.9 thrust earthquake in the western Mediterranean Sea using 19 tide gauge records. The largest trough-to-crest wave height was 196 cm recorded at the Sant Antoni station in the lee of the incoming tsunami wave. Except at one station, the first wave was not the largest wave at all the analyzed stations, and the largest wave arrived several hours after the first arrival. In addition, the tsunami waves persisted for more than 1 day at most stations. As the spectra of coastal tide gauge stations are strongly influenced by topographic features, special care was taken here while interpreting the results of spectral and wavelet analysis. Our wavelet analysis shows that only a peak at around 23 min is persistent for long duration, and other peaks at 14, 30, 45, and 60 min appeared at short durations. The 23-min signal is possibly associated with the width of the source fault whereas the fault length contributed to the 45-min signal. Based on these dominant periods, the tsunami source dimensions are estimated as 95 km × 45 km. The statistical and wavelet analyses performed here provide some new insights into the characteristics of the tsunami that was generated and propagated in the western Mediterranean basin.     

HCl emissions at Soufrière Hills Volcano,Montserrat, West Indies,during a second phase of dome building: November 1999 to October 2000

HCl:SO₂ mass ratios measured by open path Fourier transform spectroscopy (OP-FTIR) in the volcanic plume at Soufrière Hills Volcano, Montserrat, are presented for the second phase of dome building between November 1999 and November 2000. HCl:SO₂ mass ratios of greater than 1 and HCl emission rates of greater than 400 t day^–1 characterise periods of dome building for this volcano. The data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent. This is substantiated by a correlation between chlorine and water content in the melt (derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase I and II of dome growth). The matrix glass from the November 1999 and March 2000 domes indicate an open system degassing regime with a fluid-melt partition coefficient for chlorine of the order of 250–300. September 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in September and October 1997. The OP-FTIR HCl time series suggests that HCl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13.5 kt day^–1 HCl during a period of high extrusion rate in September 2000. A calculation of the HCl emission rate expected for varying extrusion rates from the open-system degassing model suggests a HCl emission rate of the order of 1–4 kt day^–1 is indicative of an extrusion rate of between 2 and 8 m³ s^–1. Monitoring of HCl at Soufrière Hills Volcano provide a proxy for extrusion rate, with changes in ratio between HCl and SO₂ occurring rapidly in the plume. Order of magnitude changes occur in HCl emission rates over the time-scale of hours to days, making these changes easy to detect during the day-to-day monitoring of the volcano. Mean water emission rates are calculated to range from 9–24 kt day^–1 during dome building activity, calculated from the predicted mass ratio of H₂O:HCl in the fluid at the surface and FTIR-derived HCl emission rates.     

Ozone concentration at meteor heights determined from forward-scatter radar echoes

The ozone concentration has been measured in the meteor zone using a method of radar echo duration distribution suggested by Jones and Šimek (1995). Data obtained by the forward-scatter system during the Lyrid meteor shower period in five consecutive years 1992–1996 agree with the Solar Mesosphere Explorer results for the same heights of 95 km. The mean value of the ozone concentration [O₃]=(1.56±0.05)×10¹⁴ m⁻³ has been derived from a total of 6596 radar meteor echoes with duration ≥1 s. The results for individual years indicating a possible decrease in [O₃] are discussed.     

Comparison of ground motions from the 2010 Mw 7.2 El Mayor–Cucapah earthquake with the next generation attenuation ground motion prediction equations

A total of 144 free-field ground motions with closest site-to-rupture distances (R_rup) less than 200 km recorded during the 2010 M_w 7.2 El Mayor–Cucapah earthquake are used to investigate predictive capabilities of the next generation attenuation (NGA) ground-motion prediction equations (GMPE). The NGA GMPEs underpredict observed spectral accelerations at sites with shear wave velocity in the upper 30 m of the site (V_s30) between 180 and 366 m/s with R_rup from about 10 to 50 km and overpredict at sites with R_rup from about 50 to 200 km. Intra-event residuals of the NGA GMPEs exhibit a noticeable negative trend for peak ground acceleration and 0.3, 1.0, and 2.0 s periods. Comparison of the inter-event residual between the 2010 M_w 7.2 El Mayor–Cucapah earthquake and the NGA dataset reveals that short-period inter-event residuals from the 2010 M_w 7.2 El Mayor–Cucapah earthquake is within the scatter of inter-event residuals from the NGA dataset but long-period inter-event residuals do not appear within of the scatter of inter-event residuals from the NGA dataset. Spectral accelerations predicted by the NGA GMPEs are generally unbiased against V_s30 and periods of less than 4.0 s. Observed spectral accelerations show a stronger V_s30 dependence for both short and long periods compared with the NGA GMPEs. The Boore and Atkinson (Earthq Spectra 24(1):99–138, 2008) and Chiou and Youngs (Earthq Spectra 24(1):173–215, 2008) GMPEs perform better in predicting observed short-period spectral accelerations at the sites with V_s30 between 180 and 250 m/s than the Abrahamson and Silva (Earthq Spectra 24(1):67–97, 2008) and Campbell and Bozorgnia (Earthq Spectra 24(1):139–171, 2008) GMPEs.     

Effectiveness of subsurface pressure monitoring for brine leakage detection in an uncertain CO2 sequestration system

This work evaluates the detection sensitivity of deep subsurface pressure monitoring within an uncertain carbon dioxide sequestration system by linking the output of an analytical reduced-order model and first-order uncertainty analysis. A baseline (non-leaky) modeling run was compared against 10 different leakage scenarios, where the cap rock permeability was increased by factors of 2–100 (cap rock permeability from 10^?3 to 10^?1 millidarcy). The uncertainty variance outputs were used to develop percentile estimates and detection sensitivity for pressure throughout the deep subsurface as a function of space (lateral distance from the injection wells and vertical orientation within the reservoir) and time (years since injection), or P(x, z, t). Conditional probabilities were computed for combinations of x, z, and t, which were then used to generate power curves for detecting leakage scenarios. The results suggest that measurements of the absolute change in pressure within the target injection aquifer would not be able to distinguish small leakage rates (i.e., less than 50 × baseline) from baseline conditions, and that only large leakage rates (i.e., >100 × baseline) would be discriminated with sufficient statistical power (>99 %). Combining measurements, for example by taking the ratio of formation pressure in Aquifer 2/Aquifer 1, provides better statistical power for distinguishing smaller leakage rates at earlier times in the injection program. Detection sensitivity for pressure is a function of space and time. Therefore, design of an adequate monitoring network for subsurface pressure should account for this space–time variability to ensure that the monitoring system performs to the necessary design criteria, e.g., specific false-negative and false-positive rates.     

Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa–Shizuoka Tectonic Line,Japan

The M_w 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa–Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2–E8) prior to the 2014 M_w 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2–E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300–400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800–1400 and is associated with the 1791 M_w 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000–700, likely corresponding to the AD 841 M_w 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600–6000 years. The throw rate during the early Holocene is estimated to be 1.2–3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7–1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.     

IR band of O<Subscript>2</Subscript> at 1.27 μm as the tracer of O<Subscript>3</Subscript> in the mesosphere and lower thermosphere: Correction of the method

The problem of systematic overestimation (20–50%) of the retrieved ozone concentrations in the altitude range of 60–80 km in the TIMED–SABER satellite experiment in the daytime has been solved. The reason for overestimation is the neglect of the electronic vibrational kinetics of photolysis products of ozone and molecular oxygen O₂(b¹Σ_g ⁺, ν) and O₂(a¹Δ_g, ν). The IR emission band of O₂(a¹Δ_g, ν = 0) at 1.27 μm can be correctly used in remote sensing in order to obtain the ozone altitude profile in the altitude range of 50–88 km only with the use of a complete model of electronic vibrational kinetics of O₂ and O₃ photolysis products (YM2011) in the Earth’s mesosphere and lower thermosphere. Alternative ozone tracers have been considered, and an optimum tracer in the altitude range of 50–100 km such as O₂(b¹Σ_g ⁺, ν = 1) molecule emissions has been proposed.     

A geostatistical approach for assessing population exposure to NO2 in a complex urban area (Beirut,Lebanon)

Few studies in the Middle East region estimated the spatial distribution of air pollutants for exposure studies. This paper presents a geostatistical approach to assess background NO₂ spatial distribution and the associated exposed population in a Mediterranean city with a complex topography, Beirut. Such modeling gave an accurate mapping of the 2010 yearly background average value of NO₂: it varies between 35 and 67 μg m^?3 with a mean of 53 μg m^?3. The mean SD of the estimated error was about 3 μg m^?3. The results showed that the spatial distribution of NO₂ follows a nested structuring, with a major structure related to topoclimatic characteristics (interaction topography/atmospheric flow at large scale) and a minor one linked to micro-environment and micro-climatic characteristics (interactions urban morphology/atmospheric flows at fine scale). The probability for the city’s inhabitants to be exposed to NO₂ levels exceeding 40 μg m^?3 threshold limit set by the World Health Organization (WHO) showed that Beirut city has a real sanitary risk to the NO₂ pollution. 93 % of the population (around 358,459 people) is 100 % sure to be exposed to a yearly average exceeding 40 μg m^?3. This knowledge will be certainly useful for developing a tool for decision support in order to implement policies of reducing air pollution in Beirut, which is, given the results, very urgent.