Wen-Whai Li

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

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Publications (18)40.72 Total impact

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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; · 3.19 Impact Factor
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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. · 3.26 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. · 3.26 Impact Factor
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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.
    Pulmonary medicine. 01/2012; 2012:736290.
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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. · 1.20 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. · 3.98 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 01/2009; 2123:17-25. · 0.44 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. 01/2008;
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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. · 3.14 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. · 1.20 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. · 1.20 Impact Factor
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    ABSTRACT: A series of analyses were performed to provide chemical signatures for surface soils and to evaluate potential sources of fugitive dust in the Paso del Norte (PdN) region. Eighteen sites were selected for soil sampling based on an assessment of the soil types in the region and the main upwind source areas with a potential for wind erosion. Analyses of the soil samples provided chemical ‘fingerprints’ of the surface soil that are presumed responsible for much of the fugitive dust loading in the region. Analysis of chemical data through multivariate statistical techniques combined with information on lithologic units, soil types, and enrichment factors identified several groups of elements associated with either natural or anthropogenic origins. Cluster analysis and principal components analysis defined four groups of elements while a redundancy analysis implied a strong association between certain elements (Ag, As, Cd, Mo, Mn, Pb, Sb) and an anthropogenic point source in the region. The conclusions from the statistical analyses are further supported by the enrichment factor (EF) analysis, using aluminum as the reference element. That is, a group of presumed anthropogenic trace elements had their highest EFs in the fine size fraction at a site close to the anthropogenic point source. Thus, the statistical analyses of surface soil data provide a useful means for quantifying the extent of anthropogenic perturbations and for highlighting some implications of contaminated fugitive dust sources.
    Science of The Total Environment 07/2004; 325:95-112. · 3.26 Impact Factor
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    ABSTRACT: Dramatic visibility reduction in the Paso del Norte Airshed (PdNA) region occurs frequently in winter, particularly during inversions and severe sandstorms. A novel methodology to determine and quantify visual deterioration of a scenic vista has been developed and presented in this paper. Using this technique, we have found that the image quality is reproducible and useful for quantitative analysis of visibility conditions in the PdNA. Regions of Interest (ROI) were selected in images along viewing paths of interest and values for a contrast variable of interest, typically the Coefficient of Variation (CV) or Contrast Ratio (CR) for discrete targets, were computed. Both these indices are bounded at zero and one and are scaled to the "clean day" maxima for a given date, time, and selected viewing path. This produces a relative visibility index for various view paths. With the siting of a Belfort (6230A) visibility monitor at a central location in the PdNA, 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 PM2.5 observations and visual inspection, we have been able to use the extinction coefficient (Bext) derived from the 6230A to put the scaled, 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 a 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 in the PdNA with other air quality indices. Multiple linear regression technique was used to derive a relationship between CR based Bext/C and air quality parameters. Visibility attenuation due to sulfate particles was found to have the highest correlation with Bext/C. In addition, solar radiation was observed to be a good predictor of visibility in the urban region.
    01/2004;
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    ABSTRACT: In this study, we determined the biologic activity of dichloromethane-extracted particulate matter < 10 micro m in aerodynamic diameter (PM10) obtained from filters at three sites in the Paso del Norte airshed, which includes El Paso, Texas, USA; Juarez, Chihuahua, Mexico, and Sunland Park, New Mexico, USA. The extracts were rich in polycyclic aromatic hydrocarbons (PAHs) and had significant biologic activity, measured using two in vitro assay systems: ethoxyresorufin-(O-deethylase (EROD) induction and the aryl hydrocarbon-receptor luciferase reporter system. In most cases, both EROD (5.25 pmol/min/mg protein) and luciferase activities (994 relative light units/mg) were highest in extracts from the Advance site located in an industrial neighborhood in Juarez. These values represented 58% and 55%, respectively, of induction associated with 1 micro M ss-naphthoflavone exposures. In contrast, little activity was observed at the Northeast Clinic site in El Paso, the reference site. In most cases, luciferase and EROD activity from extracts collected from the Tillman Health Center site, situated in downtown El Paso, fell between those observed at the other two sites. Overall, a statistically significant correlation existed between PM10 and EROD and luciferase activities. Chemical analysis of extracts collected from the Advance site demonstrated that concentrations of most PAHs were higher than those reported in most other metropolitan areas in the United States. Calculations made with these data suggest a cancer risk of 5-12 cases per 100,000 people. This risk estimate, as well as comparisons with the work of other investigators, raises concern regarding the potential for adverse health effects to the residents of this airshed. Further work is needed to understand the sources, exposure, and effects of PM10 and particulate organic material in the Paso del Norte airshed.
    Environmental Health Perspectives 08/2003; 111(10):1299-305. · 7.26 Impact Factor
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    ABSTRACT: Ten residences in El Paso, TX were monitored in the summer of 2001 for concurrent indoor and outdoor PM2.5 and PM10 10-min mass concentrations in an attempt to establish the indoor–outdoor PM correlation for typical west Texas residences equipped with evaporative coolers. Simultaneously, the modified tapered element oscillating microbalance instruments were used to collect 48-h PM2.5 and PM10 samples, both indoor and outdoor, for elemental analysis. Water samples were also taken at each home for chemical and PM correlation analysis.The air and water samples were analyzed by inductively coupled plasma–mass spectrometry, with 30 elements identifiable above detection limits in the outdoor PM10 samples and fewer elements in the PM2.5 and indoor PM10. Indoor elemental concentrations in PM10 were found to be approximately 50–70% lower than outdoor concentrations in nine of ten homes, consistent with the PM10 indoor/outdoor (I/O) mass concentrations previously reported. PM2.5 I/O ratio correlations were not as strong as for PM10; however, reduced correlations could be attributed to a pattern of recurring outlier data pairs, consisting of the same three or four elements in all ten homes.Comparison of the elemental concentrations of the evaporative cooler supply water and indoor PM demonstrated little or no correlation, yielding a conclusion that the evaporative cooler was not introducing dissolved solids from the supply water into indoor air. Overall, evaporative cooling appears to provide a cleansing of indoor air.
    Atmospheric Environment 01/2003; · 3.11 Impact Factor
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    ABSTRACT: Evaporative cooling is used extensively in low humidity areas of the Southwest United States desert region and throughout other dry climate areas worldwide for residential thermal comfort. A literature review suggested the possibility of evaporative cooling increasing personal exposures to particulate matter along with increased incidences of respiratory illnesses.Indoor and outdoor particulate matter concentrations have been measured to determine the effects of evaporative cooling on ambient air in an evaporative cooler test chamber. The test chamber experiment was conducted to better evaluate the impact of evaporative cooling without interference by household activities such as cooking, cleaning, smoking, etc. Measurement of particulate matter was performed with tapered element oscillating microbalance (TEOM) instruments to provide a larger number of data points for comparison. Based on the experiments performed on two popular models of evaporative coolers, it was found that the evaporative cooler reduces indoor PM10 by approximately 50%, and has a varying reduction effect of between 10 and 40% on PM2.5. These findings are consistent with the predicted outcomes suggested by particulate matter deposition models.
    Atmospheric Environment 01/2003; · 3.11 Impact Factor
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    ABSTRACT: Airborne particulate matter (PM) was monitored at 10 residences in the El Paso, Texas region in the summer of 2001. Concurrent indoor and outdoor 10-min averaged PM2.5 and PM10 concentrations were recorded for 2 days each to establish the indoor–outdoor PM correlation for typical west Texas residences equipped with evaporative coolers.Indoor PM concentrations stabilize in approximately 10min in a typical house equipped with evaporative coolers. If the ambient PM concentration remains steady, a 10-min average indoor air sample after the first 10-min period would contain 99% outdoor air and a 1-h average indoor air sample would actually be represented by 95% of the outdoor air. A strong diurnal pattern of PM10 indoor and outdoor was observed in 9 out of the 10 tested houses independent of the possible human activities and other indoor sources at each residence. Consistent with prior regional studies, indoor and outdoor PM10 concentrations at these houses frequently peaked with strong association with each other in the evening hours between 6 and 9pm. In addition, it is observed that both indoor and outdoor PM10 peaked after the wind speed and wind gust peaked. Indoor PM concentration peaks clearly correlated with documentation of human activities, however, these peaks tended to be of shorter duration due to the high ventilation rates of the evaporative coolers.Evaporative coolers were found to act as PM filters that effectively replace indoor air rapidly creating indoor concentrations approximately 40% of outdoor PM10 and 35% of outdoor PM2.5. Both cooler types, rigid media and aspen pad, appeared to produce similar reduction rates for both PM2.5 and PM10.
    Atmospheric Environment 01/2003; · 3.11 Impact Factor
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