Associations of Air Pollution and Pediatric Asthma in Cleveland, Ohio.

Air pollution has been associated with poor health outcomes and continues to be a risk factor for respiratory health in children. While higher particulate matter (PM) levels are associated with increased frequency of symptoms, lower lung function, and increase airway inflammation from asthma, the precise composition of the particles that are more highly associated with poor health outcomes or healthcare utilization are not fully elucidated. PM is measured quantifiably by current air pollution monitoring systems. To better determine sources of PM and speciation of such sources, a particulate matter (PM) source apportionment study, the Cleveland Multiple Air Pollutant Study (CMAPS), was conducted in Cleveland, Ohio, in 2009-2010, which allowed more refined assessment of associations with health outcomes. This article presents an evaluation of short-term (daily) and long-term associations between motor vehicle and industrial air pollution components and pediatric asthma emergency department (ED) visits by evaluating two sets of air quality data with healthcare utilization for pediatric asthma. Exposure estimates were developed using land use regression models for long-term exposures for nitrogen dioxide (NO2) and coarse (i.e., with aerodynamic diameters between 2.5 and 10 µm) particulate matter (PM) and the US EPA Positive Matrix Factorization receptor model for short-term exposures to fine (<2.5 µm) and coarse PM components. Exposure metrics from these two approaches were used in asthma ED visit prevalence and time series analyses to investigate seasonal-averaged short- and long-term impacts of both motor vehicles and industry emissions. Increased pediatric asthma ED visits were found for LUR coarse PM and NO2 estimates, which were primarily contributed by motor vehicles. Consistent, statistically significant associations with pediatric asthma visits were observed, with short-term exposures to components of fine and coarse iron PM associated with steel production. Our study is the first to combine spatial and time series analysis of ED visits for asthma using the same periods and shows that PM related to motor vehicle emissions and iron/steel production are associated with increased pediatric asthma visits.

Gaseous Oxidized Mercury Dry Deposition Measurements in the Four Corners Area, U.S.A., after Large Power Plant Mercury Emission Reductions.

Gaseous oxidized mercury (GOM) dry deposition measurements using surrogate surface passive samplers were collected at six sites in the Four Corners area, U.S.A., for the two-year period August, 2017-August, 2019, after the implementation of large power plant mercury emission reductions across the U.S.A. Two-year baseline GOM dry deposition measurements at the same six sites in the Four Corners area, taken before the implementation of U.S.A. power plant mercury control regulations, were conducted earlier from August, 2009-August, 2011. The GOM dry deposition rate estimate decreased at the Four Corners area high elevation remote mountain site of Molas Pass, Colorado (3249 m asl) from 0.4 ng/m2h for August, 2009-August, 2011 to 0.3 ng/m2h for August, 2017-August, 2019. In contrast, GOM dry deposition rate estimates for the remaining five sites increased for August, 2017-August, 2019, ranging from 0.8-1.3 ng/m2h, up from the August, 2009-August, 2011 range of 0.6-1.0 ng/m2h. Comparisons of median GOM dry deposition values showed a statistically significant decrease of 17 ng/m2 at the Molas Pass site between August, 2009-August, 2011 and August, 2017-August, 2019, and a statistically significant increase of 66 ng/m2 and 64 ng/m2, respectively, at the Mesa Verde National Park and Farmington Substation sites between August, 2009-August, 2011 and August, 2017-August, 2019. For the four years of GOM dry deposition data collected in the Four Corners area annual GOM dry deposition levels ranged from 2237 ng/m2yr (at the Molas Pass high elevation remote mountain site) to 11542 ng/m2yr (at the Mesa Verde National Park site), and the estimates were generally higher in magnitude in the spring and summer compared to the fall and winter. In light of the unexpected increases in GOM dry deposition rates at the non-remote sites, it is suggested that large regional wildfires and local anthropogenic mercury emission sources from cities and oil/gas production areas are possible notable contributors to the GOM dry deposition measurements collected in the Four Corners area.

Spatial analysis of volatile organic compounds using passive samplers in the Rubbertown industrial area of Louisville, Kentucky, USA.

Select volatile organic compounds (VOCs) were measured in the vicinity of chemical facilities and other operations in the Rubbertown industrial area of Louisville, Kentucky (USA) using modified EPA Methods 325A/B passive sampler tubes. Two-week, time-integrated passive samplers were deployed at ten sites which were aggregated into three site groups of varying distances from the Rubbertown area facilities. In comparison to canister data from 2001 to 2005, two of the sites suggested generally lower current VOC levels. Good precision was obtained from the duplicate tubes (≤ 12%) for benzene, toluene, ethylbenzene, and xylene isomers (BTEX), styrene, 1,3-butadiene, perchloroethylene, and other trace VOCs. BTEX, styrene, and 1,3-butadiene concentrations were statistically significantly higher at two site groups near Rubbertown sources than the site group farther away. As found in a similar study in South Philadelphia, BTEX concentrations were also lower for sites farther from a source, though the decline was less pronounced on a percentage basis in Rubbertown. These results suggest that EPA Methods 325A/B can be useful to assess VOC gradients for emissions from chemical facilities besides fenceline benzene levels from refineries.

Rubbertown Next Generation Emissions Measurement Demonstration Project.

Industrial facilities and other sources can emit air pollutants from fugitive leaks, process malfunctions and area sources that can be difficult to understand and to manage. Next generation emissions measurement (NGEM) approaches executed near facilities are enabling new ways to assess these sources and their impacts to nearby populations. This paper describes complementary uses of emerging NGEM systems in a Louisville, KY industrial district (Rubbertown), focusing on an important area air toxic, 1,3-butadiene. Over a one-year deployment starting in September 2017, two-week average passive samplers (PSs) at 11 sites showed both geospatial and temporal trends. At 0.24 ppbv annual average 1,3-butadiene concentration, a group of PSs located near facility fence lines was elevated compared to a PS group located in the community and upwind from facilities (0.07 ppbv average). Two elevated PS periods capturing emission events were examined using time-resolved NGEM approaches as case studies. In one event a 1.18 ppbv PS reading was found to be relatively localized and was caused by a multiday emission from a yet to be identified, non-facility source. In the other event, the airshed was more broadly impacted with PS concentrations ranging from 0.71 ppbv for the near-facility group to 0.46 ppbv for the community group. This case was likely influenced by a known emission event at an industrial facility. For both case studies, air pollutant and wind data from prototype NGEM systems were combined with source location models to inform the emission events. This research illustrates the power of applying NGEM approaches to improve both the understanding of emissions near sources and knowledge of impacts to near-source communities.

Particulate matter, nitrogen oxides, ozone, and select volatile organic compounds during a winter sampling period in Logan, Utah, USA.

Particulate matter mass (PM), trace gaseous pollutants, and select volatile organic compounds (VOCs) with meteorological variables were measured in Logan, Utah (Cache Valley), for >4 weeks during winter 2017 as part of the Utah Winter Fine Particle Study (UWFPS). Higher PM levels for short time periods and lower ozone (O3) levels were present due to meteorological and mountain valley conditions. Nitrogenous pollutants were relatively strongly correlated with PM variables. Diurnal cycles of NOx, O3, and fine PM(PM 2.5) (aerodynamic diameter <2.5 µm [PM2.5]) suggested formation from NOx. O3 levels increased from early morning into midafternoon, and NOx and PM2.5 increased throughout the morning, followed by sharp decreases. Toluene/benzene and xylenes/benzene ratios and VOC correlations with nitrogenous and PM species were indicative of local traffic sources. Wind sector comparisons suggested that pollutant levels were lower when winds were from nearby mountains to the east versus winds from northerly or southerly origins. Implications: The Cache Valley in Idaho and Utah has been designated a PM2.5 nonattainment area that has been attributed to air pollution buildup during winter stagnation events. To inform state implementation plans for PM2.5 in Cache Valley and other PM2.5 nonattainment areas in Utah, a state and multiagency federal research effort known as the UWFPS was conducted in winter 2017. As part of the UWFPS, the U.S. Environmental Protection Agency (EPA) measured ground-based PM species and their precursors, VOCs, and meteorology in Logan, Utah. Results reported here from the EPA study in Logan provide additional understanding of wintertime air pollution conditions and possible sources of PM and gaseous pollutants as well as being useful for future PM control strategies in this area.

Associations Between Residential Proximity to Traffic and Vascular Disease in a Cardiac Catheterization Cohort.

OBJECTIVE: Exposure to mobile source emissions is nearly ubiquitous in developed nations and is associated with multiple adverse health outcomes. There is an ongoing need to understand the specificity of traffic exposure associations with vascular outcomes, particularly in individuals with cardiovascular disease. APPROACH AND RESULTS: We performed a cross-sectional study using 2124 individuals residing in North Carolina, United States, who received a cardiac catheterization at the Duke University Medical Center. Traffic-related exposure was assessed via 2 metrics: (1) the distance between the primary residence and the nearest major roadway; and (2) location of the primary residence in regions defined based on local traffic patterns. We examined 4 cardiovascular disease outcomes: hypertension, peripheral arterial disease, the number of diseased coronary vessels, and recent myocardial infarction. Statistical models were adjusted for race, sex, smoking, type 2 diabetes mellitus, body mass index, hyperlipidemia, and home value. Results are expressed in terms of the odds ratio (OR). A 23% decrease in residential distance to major roadways was associated with higher prevalence of peripheral arterial disease (OR=1.29; 95% confidence interval, 1.08-1.55) and hypertension (OR=1.15; 95% confidence interval, 1.01-1.31). Associations with peripheral arterial disease were strongest in men (OR=1.42; 95% confidence interval, 1.17-1.74) while associations with hypertension were strongest in women (OR=1.21; 95% confidence interval, 0.99-1.49). Neither myocardial infarction nor the number of diseased coronary vessels were associated with traffic exposure. CONCLUSIONS: Traffic-related exposure is associated with peripheral arterial disease and hypertension while no associations are observed for 2 coronary-specific vascular outcomes.

Application of passive sorbent tube and canister samplers for volatile organic compounds at refinery fenceline locations in Whiting, Indiana.

Select volatile organic compounds (VOCs) in ambient air were measured at four fenceline sites at a petroleum refinery in Whiting, IN, using modified EPA Method 325 A/B with passive tubes and EPA Compendium Method TO-15 with canister samplers. One-week, time-integrated samplers were deployed for 8 weeks with tubes and canister samplers deployed in duplicate. Good precision was obtained from the duplicate tubes (<7%) and duplicate canisters (≤10%) for BTEX, perchloroethylene, and styrene. The tubes yielded statistically significantly higher concentrations than canisters for benzene, toluene, ethylbenzene, and m,p-xylene. However, all differences were estimated to be <0.1 ppbv. No concentration differences among the four Whiting sites were found for any of the VOCs. IMPLICATIONS: Recently enacted EPA Methods 325A/B use passive-diffusive tube samplers to measure benzene at refinery fenceline locations. This pilot study presents VOC data applying a modified version of EPA Method 325 A/B and its comparison to EPA Compendium Method TO-15 canister samplers at four refinery fenceline sites. The findings from this study provide additional confidence in application of the tube method at refineries to ascertain VOC source influence since tube and canister samplers were comparable and good precision was obtained from duplicate sampling for both methods. No overall difference in these reported VOC concentrations was found between Whiting sites for tubes or canisters.

Sample integrity evaluation and EPA method 325B interlaboratory comparison for select volatile organic compounds collected diffusively on Carbopack X sorbent tubes.

A sample integrity evaluation and an interlaboratory comparison were conducted in application of U.S. Environmental Protection Agency (EPA) Methods 325A and 325B for diffusively monitoring benzene and other selected volatile organic compounds (VOCs) using Carbopack X sorbent tubes. To evaluate sample integrity, VOC samples were refrigerated for up to 240 days and analyzed using thermal desorption/gas chromatography-mass spectrometry at the EPA Office of Research and Development laboratory in Research Triangle Park, NC, USA. For the interlaboratory comparison, three commercial analytical laboratories were asked to follow Method 325B when analyzing samples of VOCs that were collected in field and laboratory settings for EPA studies. Overall results indicate that the selected VOCs collected diffusively on sorbent tubes generally were stable for 6 months or longer when samples were refrigerated. This suggests the specified maximum 30-day storage time of VOCs collected diffusively on Carbopack X passive samplers and analyzed using Method 325B might be able to be relaxed. Interlaboratory comparison results were in agreement for the challenge samples collected diffusively in an exposure chamber in the laboratory, with most measurements within ±25% of the theoretical concentration. Statistically significant differences among laboratories for ambient challenge samples were small, less than 1 part per billion by volume (ppbv). Results from all laboratories exhibited good precision and generally agreed well with each other.

South Philadelphia passive sampler and sensor study.

UNLABELLED: From June 2013 to March 2015, in total 41 passive sampler deployments of 2 wk duration each were conducted at 17 sites in South Philadelphia, PA, with results for benzene discussed here. Complementary time-resolved measurements with lower cost prototype fenceline sensors and an open-path ultraviolet differential optical absorption spectrometer were also conducted. Minimum passive sampler benzene concentrations for each sampling period ranged from 0.08 ppbv to 0.65 ppbv, with a mean of 0.25 ppbv, and were negatively correlated with ambient temperature (-0.01 ppbv/°C, R(2) = 0.68). Co-deployed duplicate passive sampler pairs (N = 609) demonstrated good precision with an average and maximum percent difference of 1.5% and 34%, respectively. A group of passive samplers located within 50 m of a refinery fenceline had a study mean benzene concentration of 1.22 ppbv, whereas a group of samplers located in communities >1 km distant from facilities had a mean of 0.29 ppbv. The difference in the means of these groups was statistically significant at the 95% confidence level (p < 0.001). A decreasing gradient in benzene concentrations moving away from the facilities was observed, as was a significant period-to-period variation. The highest recorded 2-wk average benzene concentration for the fenceline group was 3.11 ppbv. During this period, time-resolved data from the prototype sensors and the open-path spectrometer detected a benzene signal from the west on one day in particular, with the highest 5-min path-averaged benzene concentration measured at 24 ppbv. IMPLICATIONS: Using a variation of EPA's passive sampler refinery fenceline monitoring method, coupled with time-resolved measurements, a multiyear study in South Philadelphia informed benzene concentrations near facilities and in communities. The combination of measurement strategies can assist facilities in identification and mitigation of emissions from fugitive sources and improve information on air quality complex air sheds.

Spatial analysis of volatile organic compounds in South Philadelphia using passive samplers.

UNLABELLED: Select volatile organic compounds (VOCs) were measured in the vicinity of a petroleum refinery and related operations in South Philadelphia, Pennsylvania, USA, using passive air sampling and laboratory analysis methods. Two-week, time-integrated samplers were deployed at 17 sites, which were aggregated into five site groups of varying distances from the refinery. Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) and styrene concentrations were higher near the refinery's fenceline than for groups at the refinery's south edge, mid-distance, and farther removed locations. The near fenceline group was significantly higher than the refinery's north edge group for benzene and toluene but not for ethylbenzene or xylene isomers; styrene was lower at the near fenceline group versus the north edge group. For BTEX and styrene, the magnitude of estimated differences generally increased when proceeding through groups ever farther away from the petroleum refining. Perchloroethylene results were not suggestive of an influence from refining. These results suggest that emissions from the refinery complex contribute to higher concentrations of BTEX species and styrene in the vicinity of the plant, with this influence declining as distance from the petroleum refining increases. IMPLICATIONS: Passive sampling methodology for VOCs as discussed here is employed in recently enacted U.S. Environmental Protection Agency Methods 325A/B for determination of benzene concentrations at refinery fenceline locations. Spatial gradients of VOC concentration near the refinery fenceline were discerned in an area containing traffic and other VOC-related sources. Though limited, these findings can be useful in application of the method at such facilities to ascertain source influence.

Volatile organic compounds at two oil and natural gas production well pads in Colorado and Texas using passive samplers.

UNLABELLED: A pilot study was conducted in application of the U.S. Environmental Protection Agency (EPA) Methods 325A/B variant for monitoring volatile organic compounds (VOCs) near two oil and natural gas (ONG) production well pads in the Texas Barnett Shale formation and Colorado Denver-Julesburg Basin (DJB), along with a traffic-dominated site in downtown Denver, CO. As indicated in the EPA method, VOC concentrations were measured for 14-day sampling periods using passive-diffusive tube samplers with Carbopack X sorbent at fenceline perimeter and other locations. VOCs were significantly higher at the DJB well pad versus the Barnett well pad and were likely due to higher production levels at the DJB well pad during the study. Benzene and toluene were significantly higher at the DJB well pad versus downtown Denver. Except for perchloroethylene, VOCs measured at passive sampler locations (PSs) along the perimeter of the Barnett well pad were significantly higher than PSs farther away. At the DJB well pad, most VOC concentrations, except perchloroethylene, were significantly higher prior to operational changes than after these changes were made. Though limited, the results suggest passive samplers are precise (duplicate precision usually ≤10%) and that they can be useful to assess spatial gradients and operational conditions at well pad locations over time-integrated periods. IMPLICATIONS: Recently enacted EPA Methods 325A/B use passive-diffusive tube samplers to measure benzene at multiple fenceline locations at petrochemical refineries. This pilot study presents initial data demonstrating the utility of Methods 325A/B for monitoring at ONG facilities. Measurements revealed elevated concentrations reflective of production levels and spatial gradients of VOCs relative to source proximity at the Barnett well pad, as well as operational changes at the DJB well pad. Though limited, these findings indicate that Methods 325A/B can be useful in application to characterize VOCs at well pad boundaries.

South Philadelphia passive sampler and sensor study.

From June 2013 to March 2015, in total 41 passive sampler deployments of 2 wk duration each were conducted at 17 sites in South Philadelphia, PA, with results for benzene discussed here. Complementary time-resolved measurements with lower cost prototype fenceline sensors and an open-path ultraviolet differential optical absorption spectrometer were also conducted. Minimum passive sampler benzene concentrations for each sampling period ranged from 0.08 ppbv to 0.65 ppbv, with a mean of 0.25 ppbv, and were negatively correlated with ambient temperature (-0.01 ppbv/°C, R2 = 0.68). Co-deployed duplicate passive sampler pairs (N = 609) demonstrated good precision with an average and maximum percent difference of 1.5% and 34%, respectively. A group of passive samplers located within 50 m of a refinery fenceline had a study mean benzene concentration of 1.22 ppbv, whereas a group of samplers located in communities >1 km distant from facilities had a mean of 0.29 ppbv. The difference in the means of these groups was statistically significant at the 95% confidence level (p < 0.001). A decreasing gradient in benzene concentrations moving away from the facilities was observed, as was a significant period-to-period variation. The highest recorded 2-wk average benzene concentration for the fenceline group was 3.11 ppbv. During this period, time-resolved data from the prototype sensors and the open-path spectrometer detected a benzene signal from the west on one day in particular, with the highest 5-min path-averaged benzene concentration measured at 24 ppbv. IMPLICATIONS: Using a variation of EPA's passive sampler refinery fenceline monitoring method, coupled with time-resolved measurements, a multiyear study in South Philadelphia informed benzene concentrations near facilities and in communities. The combination of measurement strategies can assist facilities in identification and mitigation of emissions from fugitive sources and improve information on air quality complex air sheds.

Association of Roadway Proximity with Fasting Plasma Glucose and Metabolic Risk Factors for Cardiovascular Disease in a Cross-Sectional Study of Cardiac Catheterization Patients.

BACKGROUND: The relationship between traffic-related air pollution (TRAP) and risk factors for cardiovascular disease needs to be better understood in order to address the adverse impact of air pollution on human health. OBJECTIVE: We examined associations between roadway proximity and traffic exposure zones, as markers of TRAP exposure, and metabolic biomarkers for cardiovascular disease risk in a cohort of patients undergoing cardiac catheterization. METHODS: We performed a cross-sectional study of 2,124 individuals residing in North Carolina (USA). Roadway proximity was assessed via distance to primary and secondary roadways, and we used residence in traffic exposure zones (TEZs) as a proxy for TRAP. Two categories of metabolic outcomes were studied: measures associated with glucose control, and measures associated with lipid metabolism. Statistical models were adjusted for race, sex, smoking, body mass index, and socioeconomic status (SES). RESULTS: An interquartile-range (990 m) decrease in distance to roadways was associated with higher fasting plasma glucose (ß = 2.17 mg/dL; 95% CI: -0.24, 4.59), and the association appeared to be limited to women (ß = 5.16 mg/dL; 95% CI: 1.48, 8.84 compared with ß = 0.14 mg/dL; 95% CI: -3.04, 3.33 in men). Residence in TEZ 5 (high-speed traffic) and TEZ 6 (stop-and-go traffic), the two traffic zones assumed to have the highest levels of TRAP, was positively associated with high-density lipoprotein cholesterol (HDL-C; ß = 8.36; 95% CI: -0.15, 16.9 and ß = 5.98; 95% CI: -3.96, 15.9, for TEZ 5 and 6, respectively). CONCLUSION: Proxy measures of TRAP exposure were associated with intermediate metabolic traits associated with cardiovascular disease, including fasting plasma glucose and possibly HDL-C.

Gaseous oxidized mercury dry deposition measurements in the southwestern USA: a comparison between Texas, eastern Oklahoma, and the Four Corners area.

Gaseous oxidized mercury (GOM) dry deposition measurements using aerodynamic surrogate surface passive samplers were collected in central and eastern Texas and eastern Oklahoma, from September 2011 to September 2012. The purpose of this study was to provide an initial characterization of the magnitude and spatial extent of ambient GOM dry deposition in central and eastern Texas for a 12-month period which contained statistically average annual results for precipitation totals, temperature, and wind speed. The research objective was to investigate GOM dry deposition in areas of Texas impacted by emissions from coal-fired utility boilers and compare it with GOM dry deposition measurements previously observed in eastern Oklahoma and the Four Corners area. Annual GOM dry deposition rate estimates were relatively low in Texas, ranging from 0.1 to 0.3 ng/m(2)h at the four Texas monitoring sites, similar to the 0.2 ng/m(2)h annual GOM dry deposition rate estimate recorded at the eastern Oklahoma monitoring site. The Texas and eastern Oklahoma annual GOM dry deposition rate estimates were at least four times lower than the highest annual GOM dry deposition rate estimate previously measured in the more arid bordering western states of New Mexico and Colorado in the Four Corners area.

Evaluation of land use regression models for nitrogen dioxide and benzene in Four US cities.

Spatial analysis studies have included the application of land use regression models (LURs) for health and air quality assessments. Recent LUR studies have collected nitrogen dioxide (NO(2)) and volatile organic compounds (VOCs) using passive samplers at urban air monitoring networks in El Paso and Dallas, TX, Detroit, MI, and Cleveland, OH to assess spatial variability and source influences. LURs were successfully developed to estimate pollutant concentrations throughout the study areas. Comparisons of development and predictive capabilities of LURs from these four cities are presented to address this issue of uniform application of LURs across study areas. Traffic and other urban variables were important predictors in the LURs although city-specific influences (such as border crossings) were also important. In addition, transferability of variables or LURs from one city to another may be problematic due to intercity differences and data availability or comparability. Thus, developing common predictors in future LURs may be difficult.

GIS-modeled indicators of traffic-related air pollutants and adverse pulmonary health among children in El Paso, Texas.

Investigators examined 5,654 children enrolled in the El Paso, Texas, public school district by questionnaire in 2001. Exposure measurements were first collected in the late fall of 1999. School-level and residence-level exposures to traffic-related air pollutants were estimated using a land use regression model. For 1,529 children with spirometry, overall geographic information system (GIS)-modeled residential levels of traffic-related ambient air pollution (calibrated to a 10-ppb increment in nitrogen dioxide levels) were associated with a 2.4% decrement in forced vital capacity (95% confidence interval (CI): -4.0, -0.7) after adjustment for demographic, anthropomorphic, and socioeconomic factors and spirometer/technician effects. After adjustment for these potential covariates, overall GIS-modeled residential levels of traffic-related ambient air pollution (calibrated to a 10-ppb increment in nitrogen dioxide levels) were associated with pulmonary function levels below 85% of those predicted for both forced vital capacity (odds ratio (OR) = 3.10, 95% CI: 1.65, 5.78) and forced expiratory volume in 1 second (OR = 2.35, 95% CI: 1.38, 4.01). For children attending schools at elevations above 1,170 m, a 10-ppb increment in modeled nitrogen dioxide levels was associated with current asthma (OR = 1.56, 95% CI: 1.08, 2.50) after adjustment for demographic, socioeconomic, and parental factors and random school effects. These results are consistent with previous studies in Europe and California that found adverse health outcomes in children associated with modeled traffic-related air pollutants.

Evaluation of land use regression models for NO2 in El Paso, Texas, USA.

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.

Spatial analysis and land use regression of VOCs and NO2 in Dallas, Texas during two seasons.

Passive air sampling for nitrogen dioxide (NO(2)) and select volatile organic compounds (VOCs) was conducted at 24 fire stations and a compliance monitoring site in Dallas, Texas, USA during summer 2006 and winter 2008. This ambient air monitoring network was established to assess intra-urban gradients of air pollutants to evaluate the impact of traffic and urban emissions on air quality. Ambient air monitoring and GIS data from spatially representative fire station sites were collected to assess spatial variability. Pairwise comparisons were conducted on the ambient data from the selected sites based on city section. These weeklong samples yielded NO(2) and benzene levels that were generally higher during the winter than the summer. With respect to the location within the city, the central section of Dallas was generally higher for NO(2) and benzene than north and south. Land use regression (LUR) results revealed spatial gradients in NO(2) and selected VOCs in the central and some northern areas. The process used to select spatially representative sites for air sampling and the results of analyses of coarse- and fine-scale spatial variability of air pollutants on a seasonal basis provide insights to guide future ambient air exposure studies in assessing intra-urban gradients and traffic impacts.

Spatial analysis and land use regression of VOCs and NO(2) from school-based urban air monitoring in Detroit/Dearborn, USA.

Passive ambient air sampling for nitrogen dioxide (NO(2)) and volatile organic compounds (VOCs) was conducted at 25 school and two compliance sites in Detroit and Dearborn, Michigan, USA during the summer of 2005. Geographic Information System (GIS) data were calculated at each of 116 schools. The 25 selected schools were monitored to assess and model intra-urban gradients of air pollutants to evaluate impact of traffic and urban emissions on pollutant levels. Schools were chosen to be statistically representative of urban land use variables such as distance to major roadways, traffic intensity around the schools, distance to nearest point sources, population density, and distance to nearest border crossing. Two approaches were used to investigate spatial variability. First, Kruskal-Wallis analyses and pairwise comparisons on data from the schools examined coarse spatial differences based on city section and distance from heavily trafficked roads. Secondly, spatial variation on a finer scale and as a response to multiple factors was evaluated through land use regression (LUR) models via multiple linear regression. For weeklong exposures, VOCs did not exhibit spatial variability by city section or distance from major roads; NO(2) was significantly elevated in a section dominated by traffic and industrial influence versus a residential section. Somewhat in contrast to coarse spatial analyses, LUR results revealed spatial gradients in NO(2) and selected VOCs across the area. The process used to select spatially representative sites for air sampling and the results of coarse and fine spatial variability of air pollutants provide insights that may guide future air quality studies in assessing intra-urban gradients.

Field comparison of passive air samplers with reference monitors for ambient volatile organic compounds and nitrogen dioxide under week-long integrals.

This study evaluates performance of nitrogen dioxide (NO2) and volatile organic compound (VOC) passive samplers with corresponding reference monitors at two sites in the Detroit, Michigan area during the summer of 2005. Ogawa passive NO2 samplers and custom-made, re-useable Perkin-Elmer (PE) tubes with Carbopack X sorbent for VOCs were deployed under week-long sampling periods for six weeks. Precise results (5% relative standard deviation, RSD) were found for NO2 measurements from collocated Ogawa samplers. Reproducibility was also good for duplicate PE tubes for benzene, toluene, ethylbenzene, and xylene isomers (BTEX species, all < or = 6% RSD). As seen in previous studies, comparison of Ogawa NO2 samplers with reference chemiluminescence measurements suggested good agreement. Generally good agreement was also found between the PE tubes and reference methods for BTEX species.