Hydrocarbon source apportionment for the 1996 Paso del Norte Ozone Study

The 1996 Paso del Norte (PdN) ozone study was conducted to improve current understanding of the significant meteorological and air quality processes that lead to high concentrations of ozone in El Paso, Texas (USA) and Ciudad Juárez, Chihuahua (Mexico). Two-hour canister samples were collected five times daily at 05.00-07.00 h, 07.00-09.00 h, 09.00-11.00 h, 11.00-13.00 h, and 15.00-17.00 h MST during intensive study periods at one urban and one rural site on each side of the border. An automated gas chromatograph was operated at one site in central El Paso. Source profiles (the fractional chemical composition of emissions) from motor vehicles, gasoline, liquefied petroleum gas, and commercial natural gas were combined with source profiles from other studies for input to the Chemical Mass Balance (CMB) receptor model to apportion the measured non-methane hydrocarbons (NMHC) to sources. On-road vehicle emissions accounted for one-half to two-thirds of the NMHC in Ciudad Juárez and El Paso with the highest contributions occurring during the morning and afternoon commute periods. Emissions from diesel exhaust contributed approximately 2-3% of NMHC in Ciudad Juárez and less than 2% in El Paso. The average sum of liquid gasoline and gasoline vapor increased during the day in Ciudad Juárez from 2% at 06.00 h to approximately 12% at 16.00 h. Diurnal and day-of-the-week patterns in the liquid gasoline contributions are essentially identical to the corresponding patterns for motor vehicle exhaust, which suggest that a large fraction of the liquid gasoline contribution may be associated with tailpipe emissions rather than evaporative emissions from motor vehicles or industrial sources. Including the sum of the two sources put the upper limit for tailpipe contributions at 60-70% of NMHC.     

The 1996 Paso del Norte Ozone Study: analysis of meteorological and air quality data that influence local ozone concentrations

The 1996 Paso del Norte Ozone Study and subsequent data analyses were implemented to develop an understanding of the chemical and physical processes which lead to high concentrations of ozone in the Paso del Norte study area which includes El Paso County, Texas, Sunland Park, New Mexico, and Ciudad Juárez, Mexico. Both the data and data analysis results are being used to support photochemical grid modeling. El Paso County and Sunland Park fail to meet the National Ambient Air Quality Standard (NAAQS) for ozone, and neighboring Ciudad Juárez fails to meet the Mexican ambient standard for ozone. This paper summarizes the measurement campaigns of the 1996 Paso del Norte Ozone Study and the findings and conclusions that arose from subsequent data analyses. Data analyses showed that high ozone concentrations resulted from a combination of conditions, including high surface temperatures, strong sunlight with few clouds, light surface winds and high concentrations of ozone precursors at ground level in the morning, and slow convective boundary layer (CBL) growth. Synoptic-scale meteorological conditions observed during high ozone episodes included an aloft high-pressure system and aloft warming. Aloft carryover of ozone and ozone precursors did not significantly contribute to high concentrations of ozone at the surface.     

Contributors to ozone episodes in three U.S./Mexico border twin-cities

The Process Analysis tools of the Community Multiscale Air Quality (CMAQ) modeling system together with back-trajectory analysis were used to assess potential contributors to ozone episodes that occurred during June 1-4, 2006, in three populated U.S.-Mexico border twin cities: San Diego/Tijuana, Imperial/Mexicali and El Paso/Ciudad Juárez. Validation of CMAQ output against surface ozone measurements indicates that the predictions are acceptable with regard to commonly recommended statistical standards and comparable to other reported studies. The mean normalized bias test (MNBT) and mean normalized gross error (MNGE) for hourly ozone fall well within the US EPA suggested range of ± 15% and 35%, respectively, except MNBT for El Paso. The MNBTs for maximum 8-h average ozone are larger than those for hourly ozone, but all the simulated maximum 8-h average ozone are within a factor of 2 of those measured in all three regions. The process and back-trajectory analyses indicate that the main sources of daytime ground-level ozone are the local photochemical production and regional transport. By integrating the effects of each process over the depth of the daytime planetary boundary layer (PBL), it is found that in the San Diego area (SD), chemistry and vertical advection contributed about 36%/48% and 64%/52% for June 2 and 3, respectively. This confirms the previous finding that high-altitude regional transport followed by fumigation contributes significantly to ozone in SD. The back-trajectory analysis shows that this ozone was mostly transported from the coastal area of southern California. For the episodes in Imperial Valley and El Paso, respectively, ozone was transported from the coastal areas of southern California and Mexico and from northern Texas and Oklahoma.     

Mexican northern border municipalities, financial dependence and institutions

Mexican northern border municipalities have experienced economic and populational growth rates that are much higher than other Mexican regions resulting in higher demand for public services and infrastructure. The different institutional framework, both fiscal and legal, faced by municipalities in every Mexican State might impact the fiscal behavior of local governments. This article examines whether border municipalities are more financially dependent on central authorities due to the high demand for public services in their jurisdictions and their inability to obtain sufficient funding. Several econometric models are estimated for 300 Mexican municipalities in the year 2000. A strong and negative relationship between income and financial dependence is found, as expected. We also learned that institutional and regional factors should not be omitted in the model specifications. Statistical theory based on the estimations shows that the border municipalities of Ciudad Juárez and Puerto Peñasco have systematically lower financial dependence than others. However, there is no general rule regarding border municipalities and financial dependence.     

Local labor markets in U.S.–Mexican border cities and the impact of maquiladora production

Shift-share decompositions of employment positions created over 1990–2002 at U.S.–Mexico border cities show that El Paso employment change has been overwhelmingly attributed to national forces, while local and national forces roughly match employment creation at Brownsville. With such fast growing U.S.–Mexico border area as background, we implement time series labor demand models to these cities (El Paso and Brownsville) and compare movements in Mexican maquiladora production against U.S. employment and wages. Cointegration methods confirm that local shocks are more important in Brownsville than in El Paso. Specifically, 10% increases in Juárez maquiladora production lead to increases of 1.21% in El Paso’s government employment and of 0.88% in overall employment. Similar increases in Matamoros lead to gains of 1.59% in Brownsville’s trade, transportation and utilities employment and of 1.41% in overall employment. These results support shift-share findings and are generally consistent with a more diversified industry-mix promoting higher employment creation.

Regional business cycle integration along the US–Mexico border

Because of the growing internationalization of the US economy, a literature has developed on the impacts of globalization on US industries and regions. In this paper we look at four MSAs that have a long history of integration with Mexico and test how their overall business cycles are connected to those of the broader economies that surround them. As globalization increases in the US, the lessons learned from these MSAs can be useful for cities trying to understand how globalization may impact them in the future. Results suggest that the border MSAs are significantly integrated with the broader economies that surround them but that the integration varies based on the structure of the local economy. Border MSAs that have large retail sectors that sell to Mexican nationals are more integrated with the Mexican economy, while El Paso, which has a close relationship with the maquiladora sector in Juarez, is more integrated with the US and Texas economies.     

Presidential address interpenetrating processes: Human agency and the becoming of regional spatial and social structures

Three critical questions are addressed through the juxtaposition of aphorisms, propositions, and empirical fragments pertaining to early nineteenth century enclosures in Skåne and the industrial restructuring of Ciudad Juárez. What about the role of human agency in the production and day-to-day perpetuation of economic landscapes, places and regions? What about structuring processes and history in regional science? How is the unbroken flow of concrete, fine-grained human activity within the region related to more macrolevel processes?     

Compilation and evaluation of a Paso del Norte emission inventory

Emission inventories of ozone precursors are routinely used as input to comprehensive photochemical air quality models. Photochemical model performance and the development of effective control strategies rely on the accuracy and representativeness of an underlying emission inventory. This paper describes the tasks undertaken to compile and evaluate an ozone precursor emission inventory for the El Paso/Ciudad Juárez/Southern Do?a Ana region. Point, area and mobile source emission data were obtained from local government agencies and were spatially and temporally allocated to a gridded domain using region-specific demographic and land-cover information. The inventory was then processed using the US Environmental Protection Agency (EPA) recommended Emissions Preprocessor System 2.0 (UAM-EPS 2.0) which generates emissions files compatible with the Urban Airshed Model (UAM). A top down evaluation of the emission inventory was performed to examine how well the inventory represented ambient pollutant compositions. The top-down evaluation methodology employed in this study compares emission inventory ratios of non-methane hydrocarbon (NMHC)/nitrogen oxide (NOx) and carbon monoxide (CO)/NOx ratios to corresponding ambient ratios. Detailed NMHC species comparisons were made in order to investigate the relative composition of individual hydrocarbon species in the emission inventory and in the ambient data. The emission inventory compiled during this effort has since been used to model ozone in the Paso del Norte airshed (Emery et al., CAMx modeling of ozone and carbon monoxide in the Paso del Norte airshed. In: Proc of Ninety-Third Annual Meeting of Air & Waste Management Association, 18-22 June 2000, Air & Waste Management Association, Pittsburgh, PA, 2000).     

Volatile organic compound measurements in the California/Mexico border region during SCOS97

Measurements of volatile organic compounds (VOC) were carried out in the California/Mexico border region during the Southern California Ozone Study in the summer of 1997 (SCOS97). Integrated 3-h samples were collected in Rosarito (south of Tijuana, Mexico) and in Mexicali during intensive operational periods (IOP), twice per IOP day. VOC were collected using stainless-steel 6-1 canisters; carbonyl compounds were collected using 2,4-dinitrophenyl-hydrazine (DNPH) impregnated C18 SepPak cartridges. The canister samples were analyzed for speciated volatile hydrocarbons (C2-C12), CO, CO2, CH4, methyl t-butyl ether (MTBE), and halogenated hydrocarbons. DNPH-impregnated cartridges were analyzed for 14 C1-C7 carbonyl compounds. The concentrations of all species were higher at Mexicali than in Rosarito. A good correlation between total non-methane hydrocarbons (TNMHC), CO, and other pollutants associated with motor vehicle emissions observed for Mexicali indicates that the main source of TNMHC at this site is vehicular traffic.     

The earnings of self-employed Mexican Americans along the U.S.-Mexico border

We utilize data from the 1990 1% Public Use Microdata Sample to analyze the earnings and occupational status of self-employed Mexican Americans in the five major U.S.-Mexico border metropolitan statistical areas (Brownsville, El Paso, Laredo, and McAllen in Texas, and San Diego, California) relative to those in non-border cities. Our findings suggest that self-employed Mexican American men earned significantly less in Texas-Mexico border cities than in other areas on average, while the earnings of self-employed Mexican American women did not significantly vary between border and non-border cities. We also find evidence that these earnings differentials may be related to differences in self-employment selection and occupational choice. As such, “across the board” policies designed to foster self-employment may not have the desired effect of boosting economic prosperity unless consideration is given to the socioeconomic and demographic composition of the region as well as to the specific occupational sector. Received: June 2000/Accepted: December 2000     

Ambient volatile organic compound (VOC) concentrations around a petrochemical complex and a petroleum refinery

Air samples were collected between September 2000 and September 2001 in Izmir, Turkey at three sampling sites located around a petrochemical complex and an oil refinery to measure ambient volatile organic compound (VOC) concentrations. VOC concentrations were 4-20-fold higher than those measured at a suburban site in Izmir, Turkey. Ethylene dichloride, a leaded gasoline additive used in petroleum refining and an intermediate product of the vinyl chloride process in the petrochemical complex, was the most abundant volatile organic compound, followed by ethyl alcohol and acetone. Evaluations based on wind direction clearly indicated that ambient VOC concentrations measured were affected by the refinery and petrochemical complex emissions. VOC concentrations showed seasonal variations at all sampling sites. Concentrations were highest in summer, followed by autumn, probably due to increased evaporation of VOCs from fugitive sources as a result of higher temperatures. VOC concentrations generally increased with temperature and wind speed. Temperature and wind speed together explained 1-60% of the variability in VOC concentrations. The variability in ambient VOC concentrations that could not be explained by temperature and wind speed can be attributed to the effect of other factors (i.e. wind direction, other VOC sources).     

Metal pollution of soils and vegetation in an area with petrochemical industry

The aim of this study was to determine the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), manganese (Mn), lead (Pb), and vanadium (V) in soil and chard samples collected in various industrial sites of Tarragona County (Spain), an area with an important number of petrochemical industries. Samples were also collected in urban (Tarragona downtown) and presumably unpolluted (blank samples) sites. Human health risks derived from metal inhalation and ingestion of soils were also assessed. With the exception of an increase in the levels of Cd and V, significant differences in soil samples from the industrial and the unpolluted zone were not found. In chard samples, significant differences between collection sites were only noted for V concentrations. For non-carcinogenic risks, the current levels of metals in the industrial area were lower than those considered as safe for the general population. In relation to carcinogenic risks, only As ingestion and Cr inhalation in the industrial zone might potentially cause an increase of the cases of cancer. A Kohonen self-organized map (an Artificial Neural Network) showed differences in metal concentrations according to the zone of origin of the samples. The current results suggest that although in general terms the petrochemical complex is not a relevant metal pollution source for the area, attention should be paid to As, Cr and V.     

Enhanced chemiluminescence as an indicator of air pollution

Investigations were conducted to determine the pollution levels of air condensate and rain samples using the enhanced chemiluminescence (ECL) reaction. Air condensate samples were initially collected from roadside sites, non‐roadside sites, smoking‐exposed sites and non‐smoking‐exposed sites using an automatic dew collector. Rainwater was also collected throughout the sampling period. Samples were subsequently analysed using the ECL reaction, and pollution levels (Eclox Units) were calculated. Air condensate samples collected from roadside‐ and smoking‐exposed sites generally had higher pollution levels than those from non‐roadside‐ and non‐smoking‐exposed sites. Samples from both smoking‐exposed and traffic‐exposed sites generally had higher pollution levels than rainwater. Finally, in samples collected from roadside‐exposed sites and rainwater, the main polluting constituents were determined to be cationic/anionic components. In samples collected from smoking‐exposed sites, the main polluting constituents were determined to be organic components.     

Source impacts by volatile organic compounds in an industrial city of southern Taiwan

This study investigates source impacts by airborne volatile organic compounds (VOC) at two sites designated for traffic and industry, in the largest industrial area Kaohsiung, southern Taiwan. The samples were collected at the two sites simultaneously during rush and non-rush hours in summer and autumn seasons. Same pattern of VOC groups were found at both sites: most abundant aromatics (78-95%) followed by alkanes (2-16%) and alkenes (0-6%). The BTEX concentration measured at the two sites ranged from 69 to 301 ppbC. Toluene, isopentane, ethylbenzene, and benzene were found to be the most abundant species. Speciation of VOCs was characterized with several skills including principal component factor analysis and BTEX characteristic ratios. Each of the resulted principal factors at the two sites explained over 80% of the VOCs data variance, and indicated that both of the sampling sites were influenced by both traffic and industrial sources with separately different levels. The remarkable patterns of the first two factors described not only the similarity but also the discrepancy at the two sampling sites, in terms of the source impacts. The high T/B ratios (7.56-14.25) observed at the industrial site implied the important impact from mobile emissions. The indicators, m,p-xylene/benzene and o-xylene/benzene, also confirmed the potential source of motor vehicles at both of the sampling sites. Air age assessment showed that more than half of the total observations located in the domain of fresh air. Low X/E ratios implied somewhat aged air mass transported to the sampling sites. The industrial site might not only encounter emissions from the industry sources, but also under unavoidable impact from the traffic sources.     

Characterization of a spatial gradient of nitrogen dioxide across a United States-Mexico border city during winter

A gradient of ambient nitrogen dioxide (NO(2)) concentration is demonstrated across metropolitan El Paso, Texas (USA), a city located on the international border between the United States and Mexico. Integrated measurements of NO(2) were collected over 7 days at 20 elementary schools and 4 air quality monitoring stations located throughout the city during typical winter atmospheric conditions. Replicate passive monitors were co-located with chemiluminescence analyzers at the monitoring stations for two consecutive 7-day periods. The passive measurements correlated with the analyzer measurements (R(2)=0.74) with precision of 2.5+/-2.2 ppb. Nitrogen dioxide concentrations ranged from 11.0 to 37.5 ppb (mean 20.6+/-7.1 ppb). In a multivariate regression model, the site elevation and distances to a main highway and to an international port of entry from Mexico explained 81% of the variance in the passive measurements. The results of this pilot study indicate that proximity to vehicle-related sources of NO(2) and site elevation are key predictors for future, more detailed assessments of vehicle-related air pollution exposure in the El Paso region.     

Propane and butane emission sources to ambient air of Mexico City metropolitan area

Samples of volatile organic compounds (VOCs) were collected in a smog chamber in order to determine whether automotive exhausts or LP Gas emissions play a greater role in the source of propane and butane, which affect ozone formation and other pollutants in the ambient air of the Mexico City metropolitan area (MCMA). These samples were collected in April 1995 during mornings and evenings. The testing methodology used for measuring exhaust emission were FTP or EPA-74 tests, and SHED type tests were also conducted in order to evaluate evaporative emissions. The finding from analysis of the VOCs collected in the morning demonstrate that in the atmosphere, propane concentrations are higher than that of butane but the reverse in evaporative and exhaust emissions, with the concentration of propane lower than that of butane. Our conclusion is that most of C3 and C4 in the ambient air comes from LP gas and not vehicle exhaust or evaporative emission, due to the higher levels of propane than butane in its formulation. The analysis of VOCs also indicates that although the conversion (in the smog chamber) of alkanes is low during the day, due to the high initial concentration, their contribution in the reaction mechanism to produce ozone can be appreciable.     

Experiments on the effects of several factors on the 1-hydroxypyrene level in human urine as an indicator of exposure to polycyclic aromatic hydrocarbons.

The concentration of 1-hydroxypyrene in human urine was determined in six volunteers who lived under the same conditions. Samples were collected four times per day for three consecutive days; the maximum concentration of 1-hydroxypyrene was found in the samples collected late in the evening (21:00-23:00 h) which is the time recommended as suitable for determination of urinary 1-hydroxypyrene for the purpose of evaluating human exposure to polycyclic aromatic hydrocarbons (PAHs). Statistical tests show that the influence of sex, age, and smoking on urinary 1-hydroxypyrene is statistically insignificant.     

Variations in amounts and potential sources of volatile organic chemicals in new cars

This study examines inter-brand, intra-brand and intra-model variations in volatile organic chemical (VOC) levels inside new cars. The effect of temperature on interior VOC levels was examined using model automobiles with and without the air-conditioning running. Potential sources of VOC were assessed by comparing VOC levels with two interior trims (leather and fabric) and by analyzing VOC emissions from various interior components. Five brands of new car, both domestic and imported, were tested. Twelve targeted VOCs were collected on solid sorbents and analyzed using thermal desorption and GC/FID. VOCs from interior parts and adhesives were identified using solid phase micro-extraction (SPME) coupled with GC/MS. The VOC concentrations varied markedly among brands and within models, and individual VOC levels ranged from below the detection limit (a few mug per cubic meter) to thousands of mug per cubic meter. The intra-model variability (mean, 47%) in the VOC levels was approximately 50% that within each brand (mean, 95%). Although interior trim levels affected VOC levels, the effects differed among brands. Reduction of the cabin temperature reduced most VOC levels, but the impact was not statistically significant. Screening tests for VOCs from interior parts revealed that butylated hydroxytoluene (BHT), a common anti-oxidant, was the most common chemical. Long-chain aliphatic hydrocarbons, particularly C14-C17, were identified in most grease (lubricant) samples, and toluene and xylenes were ubiquitously present in adhesive samples. Process-related compounds, such as plasticizer, were also identified in interior parts. In-cabin VOC levels varied significantly among makes/models and interior trims. Concerned consumers should purchase older new cars from manufacturers since VOC levels inside car cabins normally declines over time. Improved processes or materials with lower VOC emission potential should be used to minimize in-cabin VOC sources for new cars.     

Short-run maquiladora employment dynamics in Tijuana

The Tijuana maquiladora sector has grown enormously over the past two decades. Short-term time series characteristics of this segment of the regional economy are analyzed in an attempt to clarify labor market behavior associated with this remarkable performance. Parameter estimation is accomplished using linear transfer function analysis. Data are drawn from the January 1980–December 2000 sample period. Empirical results indicate that real wage rates, maquiladora plants, United States industrial activity, and the real exchange rate of the peso play significant roles in determining month-to-month fluctuations in maquiladora employment. Sub-sample simulation exercises are conducted using a random walk benchmark in order to examine forecast accuracy. Empirical results indicate that the linear transfer function technique provides relatively accurate forecasts all step-lengths.Helpful comments were provided by Tschangho John Kim, Tim Roth, Richard Posthuma, Henry Herzog, Mohammed Mohsin, and two anonymous referees. Partial financial support was provided by El Paso Electric Company, City of El Paso Office of Economic Development, and Wells Fargo Bank of El Paso.Views expressed in this study are strictly those of the authors and do not necessarily reflect the positions of the Federal Reserve Bank of Dallas or of the Federal Reserve System.Received: October 2002/Accepted: October 2003     

Polycyclic Aromatic Hydrocarbons (PAHs) in urban topsoils: Concentration and source analysis in Xuzhou,China

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments and are considered as the priority pollutants by the US Environmental Protection Agency (EPA). In this study, surface soils (0–10 cm) samples from 41 sampling sites in Xuzhou (China) were collected and analysed for 16 EPA priority polycyclic aromatic hydrocarbons via gas chromatograph/mass spectrometry (GC-MS). Total PAHs concentrations were in the range of 526 to 8612 ng/g with a mean of 2468 ng/g. Total PAHs concentrations were compared to guideline and results showed that nearly all urban soils in our study can be classified as heavily contaminated (>1000 ng/g). Carcinogenic PAHs were detected in relatively high concentrations and contributed 40.2% of the total PAHs in the urban soils. Multivariate statistical analysis including cluster analysis and factor analysis were performed and grouped the 16 PAHs under 2 clusters, which could indicate that the PAHs had different origins. The values of PAHs isomer indicated that vehicular emission might contribute to the soil PAHs in urban topsoils. The carcinogenic potency of PAH compounds was calculated and was found to be insignificant at the present level of emissions in Xuzhou.