Microbiological contamination of indoor and outdoor environments in a desert climate.

Microbiological air contamination in the desert environment is becoming an essential subject for the health of office building occupants and public health. In this study, the concentrations and compositions of airborne microorganisms (bacteria and fungi) were assessed in indoor and outdoor environments using a multistory building complex in Kuwait as a case study. Airborne microorganism samples were collected from 12 sites within the building complex containing nineteen stories over four seasons. Culturable airborne bacteria and fungi were impacted on selected media to determine their concentrations and compositions with a Biolog Omnilog GEN III system and Biolog MicroStation. The indoor mean airborne bacterial count concentrations ranged from 35 to 18,463 CFU/m3, concentrations that are higher than 2,000 CFU/m3, demonstrating high-very high contamination levels in all seasons. Fungal contamination was high in winter and summer, with detected concentrations > 2,000 CFU/m3. Indoor-to-outdoor (I/O) ratios showed that airborne microbial contamination inside building floors originated from indoor air contamination. All the building floors showed bacterial and fungal concentrations ranging from less than 2,000 to more than 2,000 CFU/m3, indicative of a high to very high air contamination level. Statistical analysis showed no correlation between bacterial and fungal concentrations, demonstrating that they originated from unrelated sources. In the indoor building air, the most prevalent bacterial isolate was Bacillus pseudomycoides/cereus, whereas the most dominant fungal isolate was Aspergillus spp. The low count for indoor air bacterial species suggested no particular health risk for the occupants. In contrast, the high count of indoor air fungal species in the winter samples and the presence of potentially allergenic genera detected may suggest possible health risks for the occupants. The results obtained are the basis for the recommendation that the maintenance activities of the HVAC system and the periodical cleaning operation program be revised and preplanned as protective measures.

Stochastic analysis of the relationship between atmospheric variables and coronavirus disease (COVID-19) in a hot, arid climate.

The rapid outbreak of the coronavirus disease (COVID-19) has affected millions of people all over the world and killed hundreds of thousands. Atmospheric conditions can play a fundamental role in the transmission of a virus. The relationship between several atmospheric variables and the transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are therefore investigated in this study, in which the State of Kuwait, which has a hot, arid climate, is considered during free movement (without restriction), partial lockdown (partial restrictions), and full lockdown (full restriction). The relationship between the infection rate, growth rate, and doubling time for SARS-CoV-2 and atmospheric variables are also investigated in this study. Daily data describing the number of COVID-19 cases and atmospheric variables, such as temperature, relative humidity, wind speed, visibility, and solar radiation, were collected for the period February 24 to May 30, 2020. Stochastic models were employed to analyze how atmospheric variables can affect the transmission of SARS-CoV-2. The normal and lognormal probability and cumulative density functions (PDF and CDF) were applied to analyze the relationship between atmospheric variables and COVID-19 cases. The Spearman's rank correlation test and multiple regression model were used to investigate the correlation of the studied variables with the transmission of SARS-CoV-2 and to confirm the findings obtained from the stochastic models. The results indicate that relative humidity had a significant negative correlation with the number of COVID-19 cases, whereas positive correlations were observed for cases of infection and temperature, wind speed, and visibility. The infection rate for SARS-CoV-2 is directly proportional to the air temperature, wind speed, and visibility, whereas inversely related to the humidity. The lowest growth rate and longest doubling time of the COVID-19 infection occurred during the full lockdown period. The results in this study may help the World Health Organization (WHO) make specific recommendations about the outbreak of COVID-19 for decision-makers around the world. Integr Environ Assess Manag 2022;18:500-516. © 2021 SETAC.

Numerical simulation of gas dispersion from rooftop stacks on buildings in urban environments under changes in atmospheric thermal stability.

The prediction of dispersion of gases emitted from rooftop stacks in a built environment is important for preventing or minimizing their harmful effects on human health. In this study, the wind flow and dispersion of exhaust gas emitted from rooftop stacks on buildings in an urban environment under different atmospheric thermal stabilities were investigated using numerical simulations. The wind flow field and dispersion contaminants were simulated using a computational fluid dynamics model with the k-ε turbulent schemes being resolved by the Reynolds-averaged Navier-Stokes approach. An isolated building was modeled under conditions of varying thermal stratification of the boundary layers (neutral, unstable, and stable conditions). The diffusion flow field within the building wake zone was investigated for various stack sites (center, right side, and left side). Experiments were conducted in a wind tunnel to validate the numerical simulation results, by using the data qualitatively and quantitatively. The numerical simulation results were consistent with the experimental observations. The results indicated that the pollutant concentration of the plume spread was high near the stack and decreased with increasing distance from the stack. Under stable conditions, the flow motion and separation increased in the wake zone, and the pollutant concentration of the lateral spread at the average human height decreased. Under unstable conditions, the flow of the vortex circulation was fast and strong, and the pollutant concentration of the vertical spread was high.

Modeling gaseous emissions and dispersion of two major greenhouse gases from landfill sites in arid hot environment.

As waste production exponentially increases, landfill continues to be the common method of waste disposal. Landfills represent significant anthropogenic sources of methane (CH4) and carbon dioxide (CO2); the main constituents of greenhouse gases (GHGs) resultant from microbial decomposition of organic waste. In the present study, ISC-AERMOD dispersion model was employed to estimate the release and dispersion rates of CH4 and CO2 from major landfill sites across Kuwait under different seasonal conditions. Results revealed that dispersions of CH4 and CO2 were influenced by the dominant northwestern and southeastern wind directions and thus, the dispersion of CH4 and CO2 extended predominantly toward northeastern direction. In terms of seasonal variation, the maximum concentrations of CH4 and CO2 were detected in winter and spring seasons, close to the landfill zone, and the dispersion of CH4 and CO2 fluxes during winter and spring seasons was longer than that during summer and fall seasons. Consequently, residential areas close to the disposal sites were exposed to higher concentrations of CH4 and CO2 gases during winter and spring. The findings of this study can serve as the basis for selecting suitable landfill locations under desert climatic conditions as determined by the distances over which gaseous emissions can diffuse.

Acute effects of air pollution on mortality: A 17-year analysis in Kuwait.

BACKGROUND: The health burden from exposure to air pollution has been studied in many parts of the world. However, there is limited research on the health effects of air quality in arid areas where sand dust is the primary particulate pollution source. OBJECTIVE: Study the risk of mortality from exposure to poor air quality days in Kuwait. METHODS: We conducted a time-series analysis using daily visibility as a measure of particulate pollution and non-accidental total mortality from January 2000 through December 2016. A generalized additive Poisson model was used adjusting for time trends, day of week, and temperature. Low visibility (yes/no), defined as visibility lower than the 25th percentile, was used as an indicator of poor air quality days. Dust storm events were also examined. Finally, we examined these associations after stratifying by gender, age group, and nationality (Kuwaitis/non-Kuwaitis). RESULTS: There were 73,748 deaths from natural causes in Kuwait during the study period. The rate ratio comparing the mortality rate on low visibility days to high visibility days was 1.01 (95% CI: 0.99-1.03). Similar estimates were observed for dust storms (1.02, 95% CI: 1.00-1.04). Higher and statistically significant estimates were observed among non-Kuwaiti men and non-Kuwaiti adolescents and adults. CONCLUSION: We observed a higher risk of mortality during days with poor air quality in Kuwait from 2000 through 2016.

Assessment of the atmospheric mixing layer height and its effects on pollutant dispersion.

The atmospheric mixing layer height (MLH) is an important parameter of the planetary boundary layer (PBL) because it affects the transportation and dispersion processes of pollutants emitted from different sources. This study investigated the relationship between the surface temperature inversion, elevated temperature inversion, and MLH within the PBL of the Kuwait by collecting and analyzing measurements of the temperature and the air quality of upper air during 2013. The upper air temperature and the MLH were derived using a microwave temperature profiler. Hourly concentrations of SO2, O3, particulate matter (PM10), NO2, CO, NO x , and non-methane hydrocarbons (NMHCs) in ambient air were measured by air quality monitoring stations. The collected data were used to estimate the hourly MLH for the transportation and dispersion of critical pollutants. The results showed that concentrations of SO2 and PM10 have direct correlation with MLH during the day, whereas they have the reverse relationship at night. Conversely, concentrations of CO, NMHCs, and NO x showed negative correlation with MLH during both day and night, whereas concentrations of O3 showed direct correlation with MLH during both day and night. In addition, the relationship between the PBL and concentrations of critical pollutants in residential areas was clarified. These findings indicate the influence of the MLH on SO2 and PM10 is much greater during the day than at night. The findings of the present study could help improve our understanding of the effects of MLH on air quality.

Numerical modeling on air quality in an urban environment with changes of the aspect ratio and wind direction.

Due to heavy traffic emissions within an urban environment, air quality during the last decade becomes worse year by year and hazard to public health. In the present work, numerical modeling of flow and dispersion of gaseous emissions from vehicle exhaust in a street canyon were investigated under changes of the aspect ratio and wind direction. The three-dimensional flow and dispersion of gaseous pollutants were modeled using a computational fluid dynamics (CFD) model which was numerically solved using Reynolds-averaged Navier-Stokes (RANS) equations. The diffusion flow field in the atmospheric boundary layer within the street canyon was studied for different aspect ratios (W/H=1/2, 3/4, and 1) and wind directions (θ=90°, 112.5°, 135°, and 157.5°). The numerical models were validated against wind tunnel results to optimize the turbulence model. The numerical results agreed well with the wind tunnel results. The simulation demonstrated that the minimum concentration at the human respiration height within the street canyon was on the windward side for aspect ratios W/H=1/2 and 1 and wind directions θ=112.5°, 135°, and 157.5°. The pollutant concentration level decreases as the wind direction and aspect ratio increase. The wind velocity and turbulence intensity increase as the aspect ratio and wind direction increase.

Experimental simulation of air quality in street canyon under changes of building orientation and aspect ratio.

To assist validation of numerical simulations of urban pollution, air quality in a street canyon was investigated using a wind tunnel as a research tool under neutral atmospheric conditions. We used tracer gas techniques from a line source without buoyancy. Ethylene (C(2)H(4)) was used as the tracer gas. The street canyon model was formed of six parallel building rows of the same length. The flow and dispersion field was analyzed and measured using a hot-wire anemometer with split fiber probe and fast flame ionization detector. The diffusion flow field in the boundary layer within the street canyon was examined at different locations, with varying building orientations (θ=90°, 112.5°, 135° and 157.5°) and street canyon aspect ratios (W/H=1/2, 3/4 and 1) downwind of the leeward side of the street canyon model. Results show that velocity increases with aspect ratio, and with θ>90°. Pollutant concentration increases as aspect ratio decreases. This concentration decreases exponentially in the vertical direction, and decreases as θ increases from 90°. Measured pollutant concentration distributions indicate that variability of building orientation and aspect ratio in the street canyon are important for estimating air quality in the canyon. The data presented here can be used as a comprehensive database for validation of numerical models.

Filtering effect of wind flow turbulence on atmospheric pollutant dispersion.

This paper presents a model for coupling the statistics of wind velocity distribution and atmospheric pollutant dispersion. The effect of wind velocity distribution is modeled as a three-dimensional finite-impulse response (3D-FIR) filter. A phase space representation of the 3D-FIR filter window is discussed. The resulting pollutant dispersion is the multiplication in the phase space of the 3-D Fourier transform of the pollutant concentration and the volume described by the filter window coefficients. The shape of the filter window in the phase space enables representing such effects as vortex shedding thermal currents, etc. The impact of spatial distribution of the sensors on the resulting pollutant spatial distribution and the 3-D FIR filter model employed also discuss. The case of a neutrally buoyant plume emitted from an elevated point source in a turbulent boundary layer considers. The results show that wind turbulence is an important factor in the pollutant dispersion and introduces expected random fluctuations in pollutant distribution and leads to spreading the distribution due to wind mixing.

Stochastic analysis of concentration field in a wake region.

INTRODUCTION: Identifying geographic locations in urban areas from which air pollutants enter the atmosphere is one of the most important information needed to develop effective mitigation strategies for pollution control. MATERIALS AND METHODS: Stochastic analysis is a powerful tool that can be used for estimating concentration fluctuation in plume dispersion in a wake region around buildings. Only few studies have been devoted to evaluate applications of stochastic analysis to pollutant dispersion in an urban area. This study was designed to investigate the concentration fields in the wake region using obstacle model such as an isolated building model. We measured concentration fluctuations at centerline of various downwind distances from the source, and different heights with the frequency of 1 KHz. Concentration fields were analyzed stochastically, using the probability density functions (pdf). Stochastic analysis was performed on the concentration fluctuation and the pdf of mean concentration, fluctuation intensity, and crosswind mean-plume dispersion. RESULTS: The pdf of the concentration fluctuation data have shown a significant non-Gaussian behavior. The lognormal distribution appeared to be the best fit to the shape of concentration measured in the boundary layer. We observed that the plume dispersion pdf near the source was shorter than the plume dispersion far from the source. CONCLUSION: Our findings suggest that the use of stochastic technique in complex building environment can be a powerful tool to help understand the distribution and location of air pollutants.

Numerical simulation on pollutant dispersion from vehicle exhaust in street configurations.

The impact of the street configurations on pollutants dispersion from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard kappa - epsilon turbulence model, which was numerically solved based on Reynolds-averaged Navier-Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three cases of street configurations: (1) a regular-shaped intersection, (2) a T-shaped intersection and (3) a Skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably well with wind tunnel results. The results obtained indicate that the mean horizontal velocity was very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and Skew-shaped street intersections. Moreover, the results reveal that the street intersections are important factors to predict the flow patterns and pollutant dispersion in street canyon.

Study on gas diffusion emitted from different height of point source.

The flow and dispersion of stack-gas emitted from different elevated point source around flow obstacles in an urban environment have been investigated, using computational fluid dynamics models (CFD). The results were compared with the experimental results obtained from the diffusion wind tunnel under different conditions of thermal stability (stable, neutral or unstable). The flow and dispersion fields in the boundary layer in an urban environment were examined with different flow obstacles. Gaseous pollutant was discharged in the simulated boundary layer over the flat area. The CFD models used for the simulation were based on the steady-state Reynolds-Average Navier-Stoke equations (RANS) with kappa-epsilon turbulence models; standard kappa-epsilon and RNG kappa-epsilon models. The flow and dispersion data measured in the wind tunnel experiments were compared with the results of the CFD models in order to evaluate the prediction accuracy of the pollutant dispersion. The results of the CFD models showed good agreement with the results of the wind tunnel experiments. The results indicate that the turbulent velocity is reduced by the obstacles models. The maximum dispersion appears around the wake region of the obstacles.

Experimental study on flow and gaseous diffusion behind an isolated building.

To assist validation of numerical models of urban pollution dispersion, the effect of obstacles building on the gaseous diffusion in the wake region have been investigated experimentally in the boundary layer wind tunnel under neutral atmospheric conditions using a tracer gas technique from a point source without buoyancy. The flow and diffusion fields in the boundary layer in an urban environment were investigated in the downwind distance of the obstacle building using an isolated high-rise building model. The scale of the model experiment was assumed to be at 1:500. In the experiment, gaseous pollutant was discharged in the simulated boundary layer over the flat terrain. The effluent velocity of the pollutant was set to be negligible. The velocity field and the turbulence characteristics were analyzed and measured using a hot wire anemometer with a split-fibre probe. The experimental technique was involved the continuous release of tracer gas from a ground level source which was located in the downwind distance of the obstacle model and measured using a fast flame ionization detector (FID). Diffusion characteristics were studied and included both the vertical and lateral mean concentrations and concentration fluctuation intensity at various downwind distances. The results of study were demonstrated that the vertical profiles of the longitudinal mean velocity are very thick around the obstacle wake region due to the turbulence mixing and the smoothing of concentration differences was increased with downwind distance from the obstacle model. Furthermore, the experimental results can help to improve the understanding of mechanisms of pollutant dispersion in an urban environment and also use to validate the corresponding computational fluid dynamics (CFD) prediction.