Wen-Whai Li

University of Texas at El Paso, El Paso, Texas, United States

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Publications (27)60.15 Total impact

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    ABSTRACT: Chronic exposure to urban traffic pollution is documented to promote atherosclerosis in adults but little is known about its potential effects in children. Our study examined the association of long-term exposure to traffic with carotid intima-media thickness (cIMT) in 287 healthy children. Residential proximity and distance-weighted traffic density (DWTD) were used as proximity markers for traffic-related air pollution exposure. The multivariable analyses revealed that children residing <100 meters from the nearest heavily trafficked road had cIMT mean and maximum measurements that were increased by 15% and 11% compared to those living ≥ 200 meters away (P = 0.0001). Similar increases in cIMT were identified for children in the highest versus lowest DWTD tertile. Children who resided 100-199 meters from traffic or in the middle DWTD tertile also exhibited increased cIMT but these differences were not statistically significant. No statistically significant differences were identified between residential distance to traffic or DWTD and systemic inflammation indicators (CRP, IL-6). The study results suggest that exposure to urban traffic promotes arterial remodeling in children. This finding is important since even small increases in cIMT over time can potentially lead to earlier progression to atherosclerosis. It is also important because traffic-related pollution is potentially modifiable.
    Journal of Environmental and Public Health 01/2015; 2015:1-11. DOI:10.1155/2015/713540
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    ABSTRACT: Children spend substantial amount of time within school microenvironments; therefore, assessing school-based exposures is essential for characterizing and preventing children's health risks to air pollutants. Indeed, the importance of characterizing children's exposures in schools is recognized by the US Environmental Protection Agency's recent initiative to promote outdoor air monitoring networks near schools. As part of a health effects study investigating the impact of traffic-related air pollution on asthmatic children along the US-Mexico border, this research examines children's exposures to, and spatio-temporal heterogeneity in concentrations of, traffic-related air pollutants at four elementary schools in El Paso, Texas. Three schools were located in an area of high traffic density and one school in an area of low traffic density. Paired indoor and outdoor concentrations of 48-h fine and coarse particulate matter (PM2.5 and PM10-2.5), 48-h black carbon (BC), 96-h nitrogen dioxide (NO2), and 96-h volatile organic compounds (VOCs) were measured for 13 weeks at each school. Outdoor concentrations of PM, NO2, BC, and BTEX (benzene, toluene, ethylbenzene, m,p-xylene, o-xylene) compounds were similar among the three schools in the high-traffic zone in contrast to the school in the low-traffic zone. Results from this study and previous studies in this region corroborate the fact that PM pollution in El Paso is dominated by coarse PM (PM10-2.5) and fine fraction (PM2.5) accounts for only 25-30% of the total PM mass in PM10. BTEX species and BC are better surrogates for traffic air pollution in this region. Correlation analyses indicate a range of association between indoor and outdoor pollutant concentrations due to uncontrollable factors like student foot traffic and varying building and ventilation configurations across the four schools. Results suggest the need of micro-scale monitoring for children's exposure assessment, which may not be adequately characterized by the measurements from a centralized monitoring site.
    Atmospheric Environment 12/2013; 80:140-151. DOI:10.1016/j.atmosenv.2013.07.056 · 3.06 Impact Factor
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    ABSTRACT: Exposure to diesel-emitted particles has been linked to increased cancer risk and cardiopulmonary diseases. Because of their size (<100 nm), exposure to ultrafine particles (UFPs) emitted from heavy-duty diesel vehicles (HDDV) might result in greater health risks than those associated with larger particles. Seasonal UFP levels at the International Bridge of the Americas, which connects the US and Mexico and has high HDDV traffic demands, were characterized. Hourly average UFP concentrations ranged between 1.7 × 10(3)/cc and 2.9 × 10(5)/cc with a mean of 3.5 × 10(4)/cc. Wind speeds <2 m s(-1) and temperatures <15 °C were associated with particle number concentrations above normal conditions. The presence of HDDV had the strongest impact on local UFP levels. Varying particle size distributions were associated with south- and northbound HDDV traffic. Peak exposure occurred on weekday afternoons. Although in winter, high exposure episodes were also observed in the morning. Particle number concentrations were estimated to reach background levels at 400 m away from traffic. The populations exposed to UFP above background levels include law enforcement officers, street vendors, private commuters, and commercial vehicle drivers as well as neighbors on both sides of the border, including a church and several schools.Journal of Exposure Science and Environmental Epidemiology advance online publication, 16 January 2013; doi:10.1038/jes.2012.119.
    Journal of Exposure Science and Environmental Epidemiology 01/2013; DOI:10.1038/jes.2012.119 · 3.05 Impact Factor
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    ABSTRACT: Exposure to traffic-related pollutants poses a serious health threat to residents of major urban centers around the world. In El Paso, Texas, this problem is exacerbated by the region's arid weather, frequent temperature inversions, heavy border traffic, and an aged, poorly maintained vehicle fleet. The impact of exposure to traffic pollution, particularly on children with asthma, is poorly understood. Tracking the environmental health burden related to traffic pollution in El Paso is difficult, especially within school microenvironments, because of the lack of sensitive environmental health indicator data. The Asthma Control Questionnaire (ACQ) is a survey tool for the measurement of overall asthma control, yet has not previously been considered as an outcome in air pollution health effect research. We conducted a repeated measure panel study to examine weekly associations between ACQ scores and traffic- and non-traffic air pollutants among asthmatic schoolchildren in El Paso. In the main one- and two-pollutant epidemiologic models, we found non-significant, albeit suggestive, positive associations between ACQ scores and respirable particulate matter (PM(10)), coarse particulate matter (PM(10-2.5)), fine particulate matter (PM(2.5)), black carbon (BC), nitrogen dioxide (NO(2)), benzene, toluene, and ozone (O(3)). Notably, associations were stronger and significant for some subgroups, in particular among subjects taking daily inhaled corticosteroids. This pattern may indicate heightened immune system response in more severe asthmatics, those with worse asthma "control" and higher ACQ scores at baseline. If the ACQ is appropriately used in the context of air pollution studies, it could reflect clinically measurable and biologically relevant changes in lung function and asthma symptoms that result from poor air quality and may increase our understanding of how air pollution influences asthma exacerbation.
    Science of The Total Environment 01/2013; 448. DOI:10.1016/j.scitotenv.2012.11.067 · 3.16 Impact Factor
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    ABSTRACT: Exposure to fine particulate matter (PM2.5) and other urban air pollutants is linked with increased cardiovascular morbidity and mortality risk in adults. However, little is known about the effect of PM2.5 exposure on child health. To investigate the hypothesis that chronic childhood exposure to urban PM2.5 promotes oxidative stress, systemic inflammation, and vascular remodeling, we conducted an epidemiologic study in 300 schoolchildren (7-12 yrs), residing in a major urban center (Quito) with distinct PM gradient zones. Data were collected on PM and other air pollutants from central air monitors, inside air monitors, and an exposure questionnaire. Other data were collected on child and household characteristics, medical history, current health, anthropometry, diet, blood glucose and lipids, and systemic inflammation and endothelium activation biomarkers. Carotid intima-media thickness (cIMT) was measured by ultrasound. Preliminary results showed that systemic inflammation, measured by IL-6, was significantly increased (mean log-scale difference= 0.49 0.07; P< 0.001) among children residing in higher compared to lower PM2.5 exposure zones (23.5 g/m3 vs. 16.4 g/m3). Higher exposure zone children exhibited greater endothelium activation, measured by higher mean E-selectin (0.72 0.07; P< 0.001) and ICAM (0.17 0.04; P < 0.001). They also had small but significantly increased cIMT compared to children in the lower exposure zone (0.02 0.01; P=0.032). These findings suggest that early childhood exposure to high PM2.5 promotes systemic inflammation and vascular remodeling. They are important since small but progressive increases in arterial wall thickness and stiffness can lead to earlier cardiovascular morbidity and mortality.
    140st APHA Annual Meeting and Exposition 2012; 10/2012
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    ABSTRACT: Traffic Air Pollution in major urban metropolitan areas of the United States can be a major health hazard for sensitive populations like the elderly, pregnant women, and young children. Two major cities: El Paso (Southwest) and Atlanta (Southeast) have developed considerably in terms of population growth and urban development in the last few years. This abstract characterizes the pollutant concentrations of major traffic air pollutants of interest like fine particulate matter (PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), and volatile organic compounds (VOCs) like benzene. Hourly data for five years (2005-2010) obtained from the various central ambient monitoring stations at both these cities would be analyzed. The time series characterization for each of these pollutants would be studied in detail and the results incorporated into Geographic Information Systems (GIS) models to tease out the year to year changes occurring over the time frame of five years. The results would add to the body of knowledge about subsequent land use pattern, population growth, and air pollution episodes in these two cities. The geospatial results would also help assess the exposure of local populations to traffic air pollution.
    2012 Society for Advancement of Hispanics/Chicanos and Native Americans in Science National Conference; 10/2012
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    ABSTRACT: Ultrafine particles (UFPs) contribute to health risks associated with air pollution, especially respiratory disease in children. Nonetheless, experimental data on UFP deposition in asthmatic children has been minimal. In this study, the effect of ventilation, developing respiratory physiology, and asthmatic condition on the deposition efficiency of ultrafine particles in children was explored. Deposited fractions of UFP (10-200 nm) were determined in 9 asthmatic children, 8 nonasthmatic children, and 5 nonasthmatic adults. Deposition efficiencies in adults served as reference of fully developed respiratory physiologies. A validated deposition model was employed as an auxiliary tool to assess the independent effect of varying ventilation on deposition. Asthmatic conditions were confirmed via pre-and post-bronchodilator spirometry. Subjects were exposed to a hygroscopic aerosol with number geometric mean diameter of 27-31 nm, geometric standard deviation of 1.8-2.0, and concentration of 1.2 × 10(6) particles cm(-3). Exposure was through a silicone mouthpiece. Total deposited fraction (TDF) and normalized deposition rate were 50% and 32% higher in children than in adults. Accounting for tidal volume and age variation, TDF was 21% higher in asthmatic than in non-asthmatic children. The higher health risks of air pollution exposure observed in children and asthmatics might be augmented by their susceptibility to higher dosages of UFP.
    07/2012; 2012:736290. DOI:10.1155/2012/736290
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    ABSTRACT: Developing suitable exposure estimates for air pollution health studies is problematic due to spatial and temporal variation in concentrations and often limited monitoring data. Though land use regression models (LURs) are often used for this purpose, their applicability to later periods of time, larger geographic areas, and seasonal variation is largely untested. We evaluate a series of mixed model LURs to describe the spatial-temporal gradients of NO(2) across El Paso County, Texas based on measurements collected during cool and warm seasons in 2006-2007 (2006-7). We also evaluated performance of a general additive model (GAM) developed for central El Paso in 1999 to assess spatial gradients across the County in 2006-7. Five LURs were developed iteratively from the study data and their predictions were averaged to provide robust nitrogen dioxide (NO(2)) concentration gradients across the county. Despite differences in sampling time frame, model covariates and model estimation methods, predicted NO(2) concentration gradients were similar in the current study as compared to the 1999 study. Through a comprehensive LUR modeling campaign, it was shown that the nature of the most influential predictive variables remained the same for El Paso between 1999 and 2006-7. The similar LUR results obtained here demonstrate that, at least for El Paso, LURs developed from prior years may still be applicable to assess exposure conditions in subsequent years and in different seasons when seasonal variation is taken into consideration.
    Science of The Total Environment 06/2012; 432:135-42. DOI:10.1016/j.scitotenv.2012.05.062 · 3.16 Impact Factor
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    ABSTRACT: Exposure to traffic-related air pollution may pose an elevated risk of respiratory harm to asthmatic children. The goal of this study was to investigate the association between exposure to specific classes of air pollutants and respiratory response in a panel of asthmatic children in El Paso, Texas. Air pollution and health response was measured at two elementary schools in El Paso with different levels of air pollution exposure. A high-exposure school was adjacent to the U.S.–Mexico border in close proximity to a major border crossing for diesel truck traffic, while the low-exposure school was in a suburban area distant from major roadways. The indoor and outdoor concentration of particle- and gas-phase pollutants was measured at each school for 13 weeks. Speciation of pollutants was performed to help identify sources. Each week, a panel of 38 asthmatic students performed pulmonary function and exhaled nitric oxide tests and completed asthma symptom questionnaires. Changes in both lung function and airway inflammation were significantly associated with pollutants with known traffic-related sources. FEV1 declined by up to 5 % in association with an interquartile range increase in the concentration of volatile organic compounds with traffic sources. Exhaled nitric oxide increased 1–5 % in association with these same compounds as well as with particulate black carbon (which also has a traffic-related source). No associations were observed between health response and pollutants with non-roadway sources. Exposure to traffic-related air pollution may lead to increased airway inflammation and decreased lung function in asthmatic children.
    Air Quality Atmosphere & Health 06/2012; 6(2). DOI:10.1007/s11869-012-0186-3 · 1.46 Impact Factor
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    ABSTRACT: The use of land-use regression (LUR) techniques for modeling small-scale variations of intraurban air pollution has been increasing in the last decade. The most appealing feature of LUR techniques is the economical monitoring requirements. In this study, principal component analysis (PCA) was employed to optimize an LUR model for PM2.5. The PM2.5 monitoring network consisted of 13 sites, which constrained the regression model to a maximum of one independent variable. An optimized surrogate of vehicle emissions was produced by PCA and employed as the predictor variable in the model. The vehicle emissions surrogate consisted of a linear combination of several traffic variables (e.g., vehicle miles traveled, speed, traffic demand, road length, and time) obtained from a road network used for traffic modeling. The vehicle-emissions surrogate produced by the PCA had a predictive capacity greater (R2=.458) than the traffic variable, Traffic Demand summarized for a 1 km buffer, with best predictive capacity (R2=.341). The PCA-based method employed in this study was effective at increasing the fit of an ordinary LUR model by optimizing the utilization of a PM2.5 dataset from small-n monitoring network. In general, the method used can contribute to LUR techniques in two major ways: 1) by improving the predictive power of the input variable, by substituting a principal component for a single variable and 2) by creating an orthogonal set of predictor variables, and thus fulfilling the no colinearity assumption of the linear regression methods. The proposed PCA method, should be universally applicable to LUR methods and will expand their economical attractiveness.
    Science of The Total Environment 03/2012; 425:27-34. DOI:10.1016/j.scitotenv.2012.02.068 · 3.16 Impact Factor
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    ABSTRACT: Traffic air pollution is a major public health concern in any urban area. This problem is compounded in the El Paso- Ciudad Juarez international region that has experienced rapid economic growth, and a substantial number of people living in close vicinity of major roadways. A growing body of air quality and epidemiologic research has discerned the linkage between traffic emissions and respiratory disorders. As part of a binational health effects study investigating the impact of traffic air pollution on asthmatic children, paired indoor and outdoor concentrations of fine and coarse PM (PM2.5 and PM10-2.5), black carbon, and NO2 were determined for 16 weeks in 2008 at four elementary schools in the international community of El Paso - Ciudad Juárez on the U.S.-Mexico border. Fifty-eight asthmatic subjects from these four schools were recruited. Health outcomes (weekly exhaled nitric oxide [eNO] measurements and daily respiratory symptoms) were recorded for the study period. Two schools (one in each city) were located in high traffic density zones and the other two in zones of low traffic density. Strong spatial heterogeneity in pollutant concentrations was observed with all outdoor pollutant concentrations higher in Ciudad Juarez than in El Paso by two-fold or more. Significant associations between the weekly (96-hr) pollutant averages and eNO with effects estimates ranging from 1 to 3% increases in eNO per interquartile range increases in pollutant concentrations were observed. Effect estimates from models using indoor pollutant school concentrations were generally more robust than corresponding models using outdoor school or ambient concentrations.
    2011 Society for Advancement of Hispanics/Chicanos and Native Americans in Science National Conference; 10/2011
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    ABSTRACT: Concerns regarding the health impact of urban air pollution on asthmatic children are pronounced along the U.S.-Mexico border because of rapid population growth near busy border highways and roads. We conducted the first binational study of the impacts of air pollution on asthmatic children in Ciudad Juarez, Mexico, and El Paso, Texas, USA, and compared different exposure metrics to assess acute respiratory response. We recruited 58 asthmatic children from two schools in Ciudad Juarez and two schools in El Paso. A marker of airway inflammation [exhaled nitric oxide (eNO)], respiratory symptom surveys, and pollutant measurements (indoor and outdoor 48-hr size-fractionated particulate matter, 48-hr black carbon, and 96-hr nitrogen dioxide) were collected at each school for 16 weeks. We examined associations between the pollutants and respiratory response using generalized linear mixed models. We observed small but consistent associations between eNO and numerous pollutant metrics, with estimated increases in eNO ranging from 1% to 3% per interquartile range increase in pollutant concentrations. Effect estimates from models using school-based concentrations were generally stronger than corresponding estimates based on concentrations from ambient air monitors. Both traffic-related and non-traffic-related particles were typically more robust predictors of eNO than was nitrogen dioxide, for which associations were highly sensitive to model specification. Associations differed significantly across the four school-based cohorts, consistent with heterogeneity in pollutant concentrations and cohort characteristics. Models examining respiratory symptoms were consistent with the null. The results indicate adverse effects of air pollution on the subclinical respiratory health of asthmatic children in this region and provide preliminary support for the use of air pollution monitors close to schools to track exposure and potential health risk in this population.
    Environmental Health Perspectives 09/2011; 120(3):437-44. DOI:10.1289/ehp.1003169 · 7.03 Impact Factor
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    ABSTRACT: Paired indoor and outdoor concentrations of fine and coarse particulate matter (PM), PM2.5 reflectance [black carbon(BC)], and nitrogen dioxide (NO(2)) were determined for sixteen weeks in 2008 at four elementary schools (two in high and two in low traffic density zones) in a U.S.-Mexico border community to aid a binational health effects study. Strong spatial heterogeneity was observed for all outdoor pollutant concentrations. Concentrations of all pollutants, except coarse PM, were higher in high traffic zones than in the respective low traffic zones. Black carbon and NO(2) appear to be better traffic indicators than fine PM. Indoor air pollution was found to be well associated with outdoor air pollution, although differences existed due to uncontrollable factors involving student activities and building/ventilation configurations. Results of this study indicate substantial spatial variability of pollutants in the region, suggesting that children's exposures to these pollutants vary based on the location of their school.
    Environmental Pollution 07/2011; 159(10):2476-86. DOI:10.1016/j.envpol.2011.06.024 · 3.90 Impact Factor
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    ABSTRACT: At night, long-haul truck drivers rest inside the cabins of their vehicles. Therefore, the in-cab air quality while air conditioning (A/C) is being provided can be a great concern to the drivers health. The effect of using different A/C methods [truck's A/C, auxiliary power unit (APU), and truck stop electrification (TSE) unit] on in-cab air quality of a heavy-duty diesel vehicle was investigated at an electrified truck stop in the El Paso, Texas, area. The research team measured the in-cabin and the ambient air quality adjacent to the parked diesel truck as well as emissions from the truck and an APU while it was providing A/C. The measured results were compared and analyzed. On the basis of these results, it was concluded that the TSE unit provided better in-cab air quality while supplying A/C. Furthermore, the truck and APU exhaust emissions were measured, and fuel consumption of the truck (while idling) and the APU (during operation) were compared. The results led to the finding that emissions from the APU were less than those from the truck's engine idling, but the APU consumed more fuel than the engine while providing A/C under given conditions.
    Transportation Research Record Journal of the Transportation Research Board 12/2009; 2123(2123):17-25. DOI:10.3141/2123-03 · 0.44 Impact Factor
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    ABSTRACT: The authors are interested in understanding the possible association between exposure to short-term fine particulate matter (PM2.5) peaks that have changing physical characteristics throughout the day and observable health outcomes (daily mortality). To this end, modern statistical methods are used here that allow for a continuous time lag between hourly PM2.5 mass concentration and daily mortality. The functional linear regression model was used to study how hourly PM2.5 mass of past days continuously influences the daily mortality count of the current day. Using a Poisson likelihood with the canonical link, the authors found that a 10-microg/m3 increase in the hourly PM2.5 above the hourly average is associated with 1.7% (0.1, 3.4), 2.4% (1.2, 3.7), 1.6% (0.6, 2.7), and 0.8% (-0.2, 1.8) higher risk of mortality on the same day, next day, 2 days, and 3 days later, respectively. The increase in relative risk is statistically significant for lags of 0-2 days, but not at lag 3. The highest association between PM2.5 mass concentration and daily mortality was found to occur in the morning when both mass and PM number concentrations peak at approximately 8:00 a.m. (lag of 15, 39, and 63 hr). This morning time interval corresponds to automobile traffic rush hour that coincides with a morning atmospheric inversion that traps high concentrations of nanoparticles.
    Journal of the Air & Waste Management Association (1995) 10/2009; 59(10):1173-85. DOI:10.3155/1047-3289.59.10.1173 · 1.17 Impact Factor
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    ABSTRACT: Particulate matter less than 10 microm (PM10) has been shown to be associated with aggravation of asthma and respiratory and cardiopulmonary morbidity. There is also great interest in the potential health effects of PM2.5. Particulate matter (PM) varies in composition both spatially and temporally depending on the source, location and seasonal condition. El Paso County which lies in the Paso del Norte airshed is a unique location to study ambient air pollution due to three major points: the geological land formation, the relatively large population and the various sources of PM. In this study, dichotomous filters were collected from various sites in El Paso County every 7 days for a period of 1 year. The sampling sites were both distant and near border crossings, which are near heavily populated areas with high traffic volume. Fine (PM2.5) and Coarse (PM10-2.5) PM filter samples were extracted using dichloromethane and were assessed for biologic activity and polycyclic aromatic (PAH) content. Three sets of marker genes human BEAS2B bronchial epithelial cells were utilized to assess the effects of airborne PAHs on biologic activities associated with specific biological pathways associated with airway diseases. These pathways included in inflammatory cytokine production (IL-6, IL-8), oxidative stress (HMOX-1, NQO-1, ALDH3A1, AKR1C1), and aryl hydrocarbon receptor (AhR)-dependent signaling (CYP1A1). Results demonstrated interesting temporal and spatial patterns of gene induction for all pathways, particularly those associated with oxidative stress, and significant differences in the PAHs detected in the PM10-2.5 and PM2.5 fractions. Temporally, the greatest effects on gene induction were observed in winter months, which appeared to correlate with inversions that are common in the air basin. Spatially, the greatest gene expression increases were seen in extracts collected from the central most areas of El Paso which are also closest to highways and border crossings.
    Toxicology and Applied Pharmacology 06/2009; 238(1):1-10. DOI:10.1016/j.taap.2009.04.021 · 3.63 Impact Factor
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    ABSTRACT: Dispersion simulations of buoyant and neutral plume releases within the recirculation cavity behind a cubical building were performed using a commercially available CFD code and the RNG k–ε turbulence model. Plume buoyancy was observed to affect the size and shape of the cavity region and the flow structure and concentration profiles within. Source momentum of a neutral plume release had similar effects on the flow structure and the cavity region to that caused by plume buoyancy. However, the effects of momentum on the concentration profiles were noticeably different from that caused by plume buoyancy. Plumes released immediately downwind of a cubical building appear to alter the flow field and dispersion characteristics of the cavity recirculation region due to their inherent momentum and buoyancy. A greater fraction of a plume was captured inside the wake as the plume became increasingly buoyant. Contrarily, greater plume momentum resulted in smaller plume fractions captured inside the wake. Inclusion of these effects in the downwash algorithms would improve the accuracy of modeling results for far-field concentration distributions and would be mandatory in accident assessments where accurate predictions of short-term, near-field concentration fluctuations near source releases are required.
    Journal of Wind Engineering and Industrial Aerodynamics 02/2008; 96(2-96):209-228. DOI:10.1016/j.jweia.2007.04.004 · 1.70 Impact Factor
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    ABSTRACT: Multivariate statistical techniques are applied to particulate matter (PM) and meteorological data to identify the sources responsible for evening PM spikes at Sunland Park, NM (USA). The statistical techniques applied are principal components analysis (PCA), redundancy analysis (RDA), and absolute principal components scores analysis (APCSA), and the data evaluated are 3-h average (6-9 p.m.) PM(2.5) mass and chemical composition and 1-h average PM(2.5) and PM(10) mass and environmental data collected in the winter of 2002. Although the interpretation of the data was complicated by the presence of sources which are likely changing in time (e.g. brick kilns), the multivariate analyses indicate that the evening high PM(2.5) is associated with burning-activities occurring to the south of Sunland Park, and these emissions are characterized by elevated Sb, Cl(-), and elemental carbon; approximately 68% of the PM(2.5) mass can be attributed to this source. The PM(10) evening peaks, on the other hand, are mainly caused by resuspended dust generated by vehicular movements south of the site and transported by the local terrain-induced drainage flow.
    Chemosphere 01/2007; 65(11):2018-27. DOI:10.1016/j.chemosphere.2006.06.071 · 3.50 Impact Factor
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    ABSTRACT: A novel methodology combining digital imaging, conventional fixed visibility monitors, and solar radiation monitors has been developed to characterize the visual air quality of the El Paso and Ciudad Juarez urban vista. The authors have found that the digital image quality is reproducible and useful for quantitative analysis of visibility conditions. Regions of interest were selected in images along view paths of interest and values for a contrast variable of interest, typically the coefficient of variation or contrast ratio (CR) for discrete targets, were computed. Both of these indices are bounded at 0 and 1 and are scaled to the "clean day" maxima for a given date, time, and selected view paths. This produces a relative visibility index for various view paths. With the siting of a Belfort (6230A) visibility monitor at a central location, it has been possible to initiate contrast analysis of various targets in current and archived camera images obtained near this monitor. For uniformly "clean" days, as indicated by fine particulate matter observations and visual inspection, the authors have been able to use the extinction coefficient (Bext) derived from the 6230A to put the relative visibility index, based on CR, on an absolute basis in terms of an ideal target located at a given distance. This permits the generation of contrast extinction, Bext/C, for each view path that is independent of the actual target intrinsic contrast (within limits) and allows the comparison of Bext/C along different view paths with other air quality indices. Multiple linear regression was used to derive a relationship between the CR-based Bext/C value and air quality parameters. Visibility attenuation because of sulfate particles was found to have the highest correlation with Bext/C. In addition, solar radiation was observed to be a significant predictor of visibility in the urban region.
    Journal of the Air & Waste Management Association (1995) 12/2005; 55(11):1733-42. DOI:10.1080/10473289.2005.10464767 · 1.17 Impact Factor
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    ABSTRACT: The causes for evening low-wind PM10 and PM2.5 peaks at Sunland Park, NM, were investigated by using wind sector analysis and by assessing relationships between PM loadings and meteorological parameters through canonical ordination analysis. Both PM10 and PM2.5 concentrations during the evening hours accounted for approximately 50% of their respective 24-hr averages, and the PM10 was mainly composed of coarse material (PM10-2.5 amounted to 77% of PM10). A wind sector analysis based on data from three surface meteorological monitoring stations in the region narrowed the potential source region for PM10 and PM2.5 to an area within a few kilometers south of Sunland Park. Canonical ordination analysis confirmed that the peak frequently occurred under stable conditions with weak southerly winds. Chemical analyses of PM showed that elemental and organic carbon (EC and OC, respectively) dominate PM2.5 and inorganic elements dominate PM10-2.5. The combined data for EC/OC, geologic elements, and various trace elements indicate that under low wind and stable conditions, traffic-related PM emissions (motor vehicle exhausts and re-suspended road dust) from the south of the site are the most likely sources for the evening PM10 and PM2.5 peaks.
    Journal of the Air & Waste Management Association (1995) 04/2005; 55(3):352-64. DOI:10.1080/10473289.2005.10464623 · 1.17 Impact Factor