Penetration of evaporative emissions into a home from an M85-fueled vehicle parked in an attached garage

The use of both oxygenated fuels in carbon monoxide (CO) nonattainment areas and reformulated gasoline in ozone nonattainment areas has been mandated by the 1990 Clean Air Act Amendments. Methanol has been proposed as an alternative fuel for CO nonattainment areas. Its use will potentially increase indoor methanol inhalation exposure resulting from the evaporation of methanol vapor from methanol-fueled vehicles parked in residential garages. Indoor air concentrations of methanol, benzene, and toluene were measured in a residential home with an attached garage. The effects of vehicle emission control devices (charcoal canister hose connection); home heating, ventilation, and air conditioning (HVAC) fans; ambient air, garage, and fuel tank temperatures; and wind speed were examined. The disconnection of the charcoal canister hose, which simulates a spent evaporative emission control device, resulted in elevated benzene, toluene, and methanol concentrations in the garage and attached home. Higher fuel tank temperatures resulted in higher benzene and toluene concentrations in the garage, but not methanol. The concentrations for all compounds in the garage and concentrations of benzene and toluene in the adjacent room were lower when the HVAC fan was on than when it was off, while the concentrations of all three compounds in the rest of the house were higher, although these differences were not statistically significant. Thus, the portion of the population that parks cars in garages attached to homes will experience increased methanol exposures if methanol is used as an automotive fuel.     

Winter indoor air pollution in Alaska: identifying a myth

The benzene and toluene levels inside three homes with attached garages were measured for 12 consecutive weeks during the winter months in Fairbanks, Alaska (Latitude 64.5 degrees N). Results for air samples collected over 12 h for the homes showed indoor benzene mixing ratios ranging from 1.6 to 20.4 parts per billion of mixing ratio volume (ppbv), and toluene air mixing ratios ranging from 7.3 to 41.6 ppbv. A correlation between benzene and toluene levels in each home and similar regression lines suggested the same major emission source, car and small equipment gasoline, present in attached garages. In one home, there was a correlation between indoor benzene mixing ratios and the urinary biomarker, trans,trans-muconic acid. Inside, air mixing ratios of benzene and toluene decreased with decreasing outside temperature in all homes studied, even though homes were relatively tight to prevent heat loss during this period of low winter outdoor temperatures. It is suggested that buildup of these pollutants indoors is prevented by the influence of an increased indoor/outdoor temperature differential and an ensuing increase in home ventilation.     

Aromatic hydrocarbons in the atmospheric environment – Part II: univariate and multivariate analysis and case studies of indoor concentrations

The concentrations of the aromatic hydrocarbons benzene, toluene, ethylbenzene and the isomeric xylenes (BTEX) have been determined in the indoor air of 115 private non-smoker homes (∼380 individual rooms) situated in areas with an extreme traffic situation, i.e. in city streets (street canyons) with high traffic density and in rural areas with hardly any traffic at all. The influence of the traffic on the indoor concentration was apparent in the high traffic area. In order to identify other factors influencing the BTEX concentrations, the data and additional questionnaires were analyzed by univariate and multivariate analysis. The analysis was supplemented by some case studies. It is shown that meteorology (the seasons), the type of room (e.g. living room versus bedroom), the ventilation and, in particular, garages in the house strongly influence the indoor concentration of BTEX. Thus, the indoor BTEX level is significantly higher in winter than in summer. Moreover, garages with a connecting door to the living quarters lead to high indoor concentrations of aromatic hydrocarbons in these rooms. In addition, the storage of solvents and hobby materials, and also the presence of smoking guests increase the BTEX level. If rooms are directly heated by coal or wood, the BTEX level is higher compared to the use of gas heating. Surprisingly, no correlation was found between the building materials used and the BTEX level. Case studies were carried out for two homes with an integrated garage (and a connecting door to the living rooms) and for seven homes where redecoration work was carried out during sampling. In both instances, a pronounced increase was observed in the BTEX concentration.     

Reductions in human benzene exposure in the California South Coast Air Basin

Benzene typically contributes a significant fraction of the human cancer risk associated with exposure to urban air pollutants. In recent years, concentrations of benzene in ambient air have declined in many urban areas due to the use of reformulated gasolines, lower vehicle emissions, and other control measures. In the California South Coast Air Basin (SoCAB) ambient benzene concentrations have been reduced by more than 70% since 1989. To estimate the resulting effect on human exposures, the Regional Human Exposure (REHEX) model was used to calculate benzene exposures in the SoCAB for the years 1989 and 1997. Benzene concentration distributions in 14 microenvironments (e.g. outdoor, home, vehicle, work) were combined with California time-activity patterns and census data to calculate exposure distributions for 11 demographic groups in the SoCAB. For 1997, the calculated average benzene exposure for nonsmoking adults in the SoCAB was 2 ppb, compared to 6 ppb for 1989. For nonsmokers, about half of the 1997 exposure was due to ambient air concentrations (including their contributions to other microenvironments), but only 4% for smokers. Passive tobacco smoke contributed about one-fourth of all exposure for adult nonsmokers. In-transit microenvironments and attached garages contributed approximately 15 and 10%, respectively. From 1989 to 1997, decreases in passive smoke exposure accounted for about one-sixth of the decrease in exposure for nonsmoking adults, with the remainder due to decreases in ambient concentrations. The reductions in exposure during this time period indicate the effectiveness of reformulated fuels, more stringent emission standards, and smoking restrictions in significantly reducing exposure to benzene.     

A comparison of PAMS and air toxics measurements

One of the requirements of the 1990 Clean Air Act Amendments (CAA) is that 1-h ozone nonattainment areas that are classified severe or higher category are required to operate a network of photochemical assessment monitors (PAMS) to provide hourly measurements of volatile organic compounds (VOCs) comprising of Carbon number <12 (C2–C12), along with carbonyl measurements at 3-h intervals during the summer ozone season. Often collocated with PAMS are 24-h-integrated canister and cartridge-based measurements of selected air toxic compounds, thereby providing an opportunity for inter-comparison and validation of both sets of data. In this study, we report such a comparison and estimates of trend for benzene, m-, p- and o-xylene, toluene, ethylbenzene, 1,2,4-trimethylbenzene, formaldehyde and acetaldehyde at Bronx, NY. The analysis shows that hourly PAMS and 24-h-integrated air toxics are in good agreement with each other exhibiting similar trends and that the PAMS with the higher temporal resolution offers information on excursions of the toxic compounds that would be quite useful in assessment of acute health effects. These findings were also found to be applicable to other locations such as South De Kalb, GA; Gary, IN and Lynn, MA.     

Measured carbon monoxide concentrations from stock and reduced-emission prototype portable generators operated in an attached garage

There is concern about the hazard of acute residential CO exposures from portable gasoline-powered generators, which can result in death or serious adverse health effects in exposed individuals. To address this hazard, the U.S. Consumer Product Safety Commission has developed low CO emission prototype generators by adapting off-the-shelf emission control technologies onto commercially available generators. A series of tests was conducted to characterize the indoor CO concentrations resulting from portable generators operating in the attached garage of a research house under seven different test house/garage configurations. The tested generators include both unmodified and modified low CO emission prototypes. It was found that CO concentrations varied widely, with peak house CO concentrations ranging from under 10 ppm to over 10,000 ppm. The highest concentrations in the house resulted from operation of the unmodified generator in the garage with the garage bay door closed and the house access door open. The lowest concentrations resulted from operation of a modified low CO emission prototype in the garage with the garage bay door open and the house access door closed. These tests documented reductions of up to 98% in CO concentrations due to emissions from two low CO emission portable generators compared to a stock generator.

Implications: Improper portable generator use has caused 800 U.S. deaths in the past 14 years. Generators operated in attached garages can cause CO to quickly reach deadly levels. Two low-emission prototypes generators were tested and had CO emissions reduced by up to 98%. Low-emission generators can reduce the risk of consumer poisonings and deaths.     

Effect of Methanol on Exhaust Composition of a Fuel Containing Toluene,n-Heptane,and Isooctane

This study describes the variations in the chemical composition of the exhaust from a single cylinder engine when up to 25% methanol is added to a fuel blend of toluene, isooctane, and n-heptane. Under fuel-rich conditions, and with increasing methanol concentration, it is observed that unburned fuel and benzene emissions increase, exhaust acetylene remains constant, and propylene, isobutylene, methane, ethylbenzene, and styrene concentrations decrease. As oxygen becomes more available, the effects of methanol are reduced, and at an equivalence ratio of 1.25—excess oxygen now is present—methanol no longer affects the concentration of exhaust hydrocarbons. These observations are explained by the reactions of formaldehyde—an incomplete combustion product of methanol— with alkyl radicals derived from the fuel. The photochemical reactivity of the exhaust is unchanged when up to 15% of methanol is present in the fuel at an equivalence ratio of 0.85, but increases at higher methanol contents because of the increase in unburned toluene in the exhaust.     

Contribution of vehicle emissions from an attached garage to residential indoor air pollution levels

The infiltration of vehicle emissions into a house from the attached garage was studied for 16 homes of differing designs using the same extensively characterized vehicle at each home. Before the in-home measurement program, the cold-start and hot-start tailpipe emissions and hot-soak evaporative emissions from a 1993 Buick Regal were measured using standard vehicle emissions measurement methods. The emissions were chemically characterized for methane, nonmethane hydrocarbons (NMHC), and carbonyl compounds. The in-home measurements occurred over two winter seasons (1997-1998 and 1998-1999) in Ottawa, Ontario, Canada. Samples of indoor air and garage atmosphere were characterized for carbon monoxide, carbon dioxide, methane, NMHC, and carbonyl compounds. During the second year, real-time measurements of carbon, carbon dioxide, and total hydrocarbons were made to determine when and for how long the emissions plume infiltrates the house. Chemical mass balance modeling results using 31 NMHC species suggest that between 9 and 71% of the concentrations measured in the house during the hot-soak test and between 13 and 85% of the concentrations measured in the house during the cold-start test could be attributed to vehicle emissions infiltrating from the garage. In contrast, increases in carbonyl compound concentrations caused by the vehicle were difficult to detect above the already significant levels found in the houses.     

Influence of Oxygenated Fuels on the Emissions from Three Pre-1985 Light-Duty Passenger Vehicles

Tailpipe and evaporative emissions from three pre-1985 passenger motor vehicles operating on an oxygenated blend fuel and on a nonoxygenated base fuel were characterized. Emission data were collected for vehicles operating over the Federal Test Procedure at 40,75, and 90°F to simulate ambient driving conditions. The two fuels tested were a commercial summer grade regular gasoline (the nonoxygenated base fuel) and an oxygenated fuel containing 9.5 percent methyl tert-butyl ether (MTBE), more olefins, and fewer aromatics than the base fuel. The emissions measured were total hydrocarbons (THCs), speciated hydrocarbons, speciated aldehydes, carbon monoxide (CO), oxides of nitrogen (NO_x), benzene, and 1,3-butadiene.

This study showed no pattern of tailpipe regulated emission reduction when oxygenated fuel was used. Tailpipe emissions from the 1984 Buick Century without a catalyst and the 1977 Mustang with catalyst decreased with the MTBE fuel. However, emissions from the 1984 Buick Century and the 1980 Chevrolet Citation, both fitted with catalysts increased. The vehicles emitted more 1,3- butadiene and, in general, more NO_x when operated with the base fuel.

THC, CO, benzene, and 1,3-butadiene emissions from both fuels and all vehicles, in general, decreased with increasing test temperature, whereas NO_x emissions, in general, increased with increasing test temperature. Formaldehyde, acetaldehyde, and total aldehydes also showed a decrease in emissions as test temperature increased. More formaldehyde was emitted when the MTBE fuel was used.

Evaporative, diurnal, and hot soak emissions from the base fuel were greater than those from the MTBE fuel. The evaporated emissions from both fuels increased with increasing test temperatures. Diurnal data indicate that canister conditioning (bringing the evaporative charcoal canister to equilibrium) is required before testing.     

Speciated Hydrocarbon Emissions from the Combustion of Single Component Fuels. II. Catalyst Effects

Six single-component fuels (isooctane, n-heptane, 1-hexene, cyclohexane, methyl-t-butyl ether (MTBE), and toluene) and a multicomponent tracer fuel were burned in a pulse flame combustor (PFC) and reacted over a three-way automotive catalyst. The composition of the raw, uncatalyzed PFC exhaust was characterized in Part I of this study. In Part II, we focus on the conversions of the individual exhaust HC species over the catalyst. In accord with previous studies, the order of reactivity observed for the various classes of HC species was: methane (least reactive) < saturated HC < aromatics < unsaturated HC (most reactive). These differences in catalytic reactivity led to increases in the relative concentrations of methane and some saturated hydrocarbons in the post catalyst exhaust, and corresponding decreases in the relative concentrations of aromatic and unsaturated hydrocarbons. Oxygenated organic compounds showed wide variability in catalytic reactivity depending on the specific compounds involved. Catalytic conversion of the air toxic, 1,3-butadiene, was essentially complete to within detection limits. Benzene and toluene appeared to have similar intrinsic catalytic reactivities. However, net conversion of benzene in most instances was significantly less than that of toluene owing to demethylation of toluene (to form benzene) occurring in parallel with benzene oxidation. Rich combustion of both isooctane and tracer fuel led to the production of methane by the catalyst, primarily from reactions of acetylene and small olefins.     

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.     

Concentrations of benzene and toluene in the atmosphere of the southwestern area at the Mexico City Metropolitan Zone

The Mexico City Metropolitan Zone (MCMZ) presents important emissions of hazardous air pollutants. It is well documented that the MCMZ suffers a critical air pollution problem due to high ozone and particulate matter concentrations. However, toxic air pollutants such as benzene and toluene have not been considered. Benzene has accumulated sufficient evidence as a human carcinogen, and the ratio benzene/toluene is an excellent indicator to evaluate control strategies efficiency.In order to evaluate the levels of these two air toxic pollutants in the MCMZ, ambient air samples were collected in canisters and analyzed with a gas chromatograph with a flame ionization detector, according to procedures described in the United States Environmental Protection Agency (USEPA) method TO-15. Quality assurance was performed collecting duplicate samples which were analyzed in replicate to quantify the precision of air-quality measurements.Three different sites located in the Southwestern area in the MCMZ were selected for the sampling: the University campus, a gas station, and a vertical condominium area, in the same neighborhood, which presents different activities. At these sites, grab air samples were collected during the morning hours (7–8 a.m.), while for the University area, 24 h integrated air samples were collected simultaneously, with grab samples.Benzene concentrations (24 h sampling) in the atmosphere around the University campus have similar present levels as in other cities of North America. Mean values in this site were about 1.7 ppb.A significant variation exists between the benzene and toluene concentrations in the studied sites, being the more critical values than those registered at the gas station (an average of 25.8 ppb and a maximum of 141 ppb of benzene). There is a fuel regulation for gasoline in Mexico, which allows a maximum of 1 percent of benzene. However, since more than 60 percent of vehicles do not have catalytic converters (models before 1991) it is expected that most of this benzene be emitted through exhaust pipe. Another strategy being implemented is the use of vapor recovery systems at the gas stations. Vehicles emission control technology must be matched with adequate fuel characteristics in the problem area where it will be implemented, to achieve maximum emission reductions.     

Speciated non-methane organic compounds emissions from food cooking in Mexico

Non-methane organic compound (NMOC) emissions from different sorts of food preparation sites, were quantified for the first time in Mexico, in order to develop emission profiles for further application in the chemical mass balance receptor model (CMB). Restaurants using charcoal grills and LP gas stoves, “tortillerı́as”, food frying places and rotisseries were sampled using SUMMA^® stainless-steel canisters to analyse NMOC by high-resolution gas chromatography. The results obtained show that profiles determined from food cooking processes have similarities to those found in LP gas combustion, which is the most common fuel in Mexico used for this purpose, although there were differences in the relative composition of propane and butane in both cases. This suggests that, the rates of combustion of propane and butane are different. It has also been detected that propene, a reactive olefin is produced during the combustion process. The obtained profiles of restaurants, rotisseries and fried food show an important contribution of two carbon compounds (ethane, ethylene and acetylene) that can be attributed to the complex process of grease and meat cooking. The presence of these compounds cannot be attributed to vehicular sources since the concentrations are higher than in ambient air. These were also determined from aromatic compounds such as benzene, toluene and xylene in the combustion of vegetal charcoal. The measured concentrations indicate that NMOC emissions from cooking may become an important indoor source of NMOC under crowded conditions in closed places.     

汽车内微环境空气污染的初步探究

为了研究车内的污染水平,在2004-04-10至2004-06-20对车内空气进行了采样和分析.对车龄在2年内的91种型号轿车的车内微环境进行了静态检测,有效检测车辆共计802辆,同时对比检测20辆2002年以前出厂的旧车.检测项目包括甲醛、苯、甲苯、二甲苯和CO等.参照国家室内空气质量标准,新车中甲苯浓度超标率达82%,苯和甲醛浓度的超标率分别为75%和24%.在被检测车辆中,甲醛、苯、甲苯和二甲苯浓度均是新车比旧车高,只有CO浓度是旧车比新车高.初步分析判断苯系物主要来源于车内的胶粘剂,甲醛来自于车椅座套和座垫等,CO来源于发动机排放残留.     

Speciated Hydrocarbon Emissions from the Combustion of Single Component Fuels. I. Effect of Fuel Structure

Speciated hydrocarbon emissions data have been collected for six single-component fuels run in a laboratory pulse flame combustor (PFC). The six fuels include n-heptane, isooctane (2, 2, 4-trimethylpentane), cyclohexane, 1-hexene, toluene, and methyl-t-butyl ether (MTBE: an oxygenated fuel extender). Combustion of non-aromatic fuels in the PFC (at a fuel/air equivalence ratio of Φ = 1.02) produced low levels of unburned fuel and high yields of methane and olefins (> 75 percent combined) irrespective of the molecular structure of the fuel. In contrast, hydrocarbon emissions from toluene combustion in the PFC were comprised predominantly of unburned fuel (72 percent). With the PFC, low levels of 1, 3-butadiene (0.3-1.8 percent) were observed from all the fuels except MTBE, for which no measurable level (<0.2 percent) was detected; low levels of benzene were observed from isooctane, heptane, and 1-hexene, but significant levels (9 percent) from cyclohexane and toluene. No measurable amount of benzene (< 0.2 percent) was observed in the MTBE exhaust.

For isooctane and toluene the speciated hydrocarbon emissions from a spark-ignited (SI) single-cylinder engine were also determined. HC emissions from the SI engine contained the same species as observed from the PFC, although the relative composition was different. For the non-aromatic fuel isooctane, unburned fuel represented a larger fraction (50 percent) of the HC emissions when run in the engine. HC emissions from toluene combustion in the engine were similar to those from the PFC.     

Characterizing relationships between personal exposures to VOCs and socioeconomic,demographic, behavioral variables

Socioeconomic and demographic factors have been found to significantly affect time-activity patterns in population cohorts that can subsequently influence personal exposures to air pollutants. This study investigates relationships between personal exposures to eight VOCs (benzene, toluene, ethylbenzene, o-xylene, m-,p-xylene, chloroform, 1,4-dichlorobenzene, and tetrachloroethene) and socioeconomic, demographic, time-activity pattern factors using data collected from the 1999–2000 National Health and Nutrition Examination Survey (NHANES) VOC study. Socio-demographic factors (such as race/ethnicity and family income) were generally found to significantly influence personal exposures to the three chlorinated compounds. This was mainly due to the associations paired by race/ethnicity and urban residence, race/ethnicity and use of air freshener in car, family income and use of dry-cleaner, which can in turn affect exposures to chloroform, 1,4-dichlorobenzene, and tetrachloroethene, respectively. For BTEX, the traffic-related compounds, housing characteristics (leaving home windows open and having an attached garage) and personal activities related to the uses of fuels or solvent-related products played more significant roles in influencing exposures. Significant differences in BTEX exposures were also commonly found in relation to gender, due to associated significant differences in time spent at work/school and outdoors. The coupling of Classification and Regression Tree (CART) and Bootstrap Aggregating (Bagging) techniques were used as effective tools for characterizing robust sets of significant VOC exposure factors presented above, which conventional statistical approaches could not accomplish. Identification of these significant VOC exposure factors can be used to generate hypotheses for future investigations about possible significant VOC exposure sources and pathways in the general U.S. population.     

Multi-zonal air flow rates in residences in Boston,Massachusetts

In spite of the importance of interzonal air flow for indoor air quality assessment, few studies have characterized these flows. As part of the Boston Exposure Assessment in Microenvironments (BEAM) Study, air flow rates were estimated within 45 residences in the Boston area, most over two seasons. Thirty-five residences had basements, 11 of which also had attached garages, and 10 other residences had common apartment hallways. Air flow rates between zones were calculated using tracer gases (PFTs and SF6) and mass-balance models. Mean air flow rates from the basement to the occupied zone were significantly higher in the winter (174 m³ h⁻¹) than in the summer (67 m³ h⁻¹). The mean percent of the total air flow within the occupied zone of the residence from the basement was 26% (SD=34%) in the summer and 47% (SD=26%) in the winter while the mean percent from apartment hallways was 22% (SD=33%). Residences with garages attached to the basement had higher air flow rates to the adjacent zone (means from 50 to 887 m³ h⁻¹) than those with garages attached directly to the occupied zone (means from 1 to 65 m³ h⁻¹). These data provide a basis for modeling the contribution of indoor sources to concentrations in occupied zones.     

Modeling of Personal Exposures to Ambient Air Toxics in Camden,New Jersey: An Evaluation Study

Abstract

This study presents the Individual Based Exposure Modeling (IBEM) application of MENTOR (Modeling ENvironment for TOtal Risk studies) in a hot spot area, where there are concentrated local sources on the scale of tens to hundreds of meters, and an urban reference area in Camden, NJ, to characterize the ambient concentrations and personal exposures to benzene and toluene from local ambient sources. The emission-based ambient concentrations in the two neighborhoods were first estimated through atmospheric dispersion modeling. Subsequently, the calculated and measured ambient concentrations of benzene and toluene were separately combined with the time-activity diaries completed by the subjects as inputs to MENTOR/IBEM for estimating personal exposures resulting from ambient sources. The modeling results were then compared with the actual personal measurements collected from over 100 individuals in the field study to identify the gaps in modeling personal exposures in a hot spot. The modeled ambient concentrations of benzene and toluene were generally in agreement with the neighborhood measurements within a factor of 2, but were underestimated at the high-end percentiles. The major local contributors to the benzene ambient levels are from mobile sources, whereas mobile and stationary (point and area) sources contribute to the toluene ambient levels in the study area. This finding can be used as guidance for developing better air toxic emission inventories for characterizing, through modeling, the ambient concentrations of air toxics in the study area. The estimated percentage contributions of personal exposures from ambient sources were generally higher in the hot spot area than the urban reference area in Camden, NJ, for benzene and toluene. This finding demonstrates the hot spot characteristics of stronger local ambient source impacts on personal exposures. Non-ambient sources were also found as significant contributors to personal exposures to benzene and toluene for the population studied.     

Volatile organic compounds (VOCs) in urban atmosphere of Hong Kong

The assessment of volatile organic compounds (VOCs) has become a major issue of air quality network monitoring in Hong Kong. This study is aimed to identify, quantify and characterize volatile organic compounds (VOCs) in different urban areas in Hong Kong. The spatial distribution, temporal variation as well as correlations of VOCs at five roadside sampling sites were discussed. Twelve VOCs were routinely detected in urban areas (Mong Kok, Kwai Chung, Yuen Long and Causeway Bay). The concentrations of VOCs ranged from undetectable to 1396 microg/m3. Among all of the VOC species, toluene has the highest concentration. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the major constituents (more than 60% in composition of total VOC detected), mainly contributed from mobile sources. Similar to other Asian cities, the VOC levels measured in urban areas in Hong Kong were affected both by automobile exhaust and industrial emissions. High toluene to benzene ratios (average T/B ratio = 5) was also found in Hong Kong as in other Asian cities. In general, VOC concentrations in the winter were higher than those measured in the summer (winter to summer ratio > 1). As toluene and benzene were the major pollutants from vehicle exhausts, there is a necessity to tighten automobile emission standards in Hong Kong.     

Roadside and in-vehicle concentrations of monoaromatic hydrocarbons

Airborne concentrations of benzene, toluene and the xylenes have been measured inside passenger cars whilst driven along major roads in the city of Birmingham, UK, as well as immediately outside the car, and at the roadside. A comparison of concentrations measured in the car with those determined from immediately outside showed little difference, with a mean ratio for benzene of 1.17±0.34 and for toluene 1.11±0.16 (n=53). The ratio of in-car to roadside concentration was rather higher at 1.55±0.68 for benzene and 1.54±0.72 for toluene (n=53). The roadside concentrations were typically several-fold higher than those measured at a background suburban monitoring station within Birmingham, although much variation was seen between congested and uncongested roads, with concentrations adjacent to uncongested roads similar to those measured at the background monitoring station. Measurements of benzene and toluene in a car driven on a rural road outside the city showed very comparable in-car and out-of-car concentrations strengthening the conclusion that pollution inside the car is derived from pollutants outside entering with ventilation air. The exceptions were an older car where in-car concentrations appreciably exceeded those outside (in-to out-vehicle ratio=2.3 for benzene and 2.2 for toluene where n=5) indicating probable self-contamination, and a very new car which built up increased VOC concentrations when stationary without ventilation (in-to out-vehicle ratio=2.4 for benzene and 3.3 for toluene where n=5). A further set of measurements inside London taxi cabs showed concentrations to be influenced by the area within which the taxi was driven, the traffic density and the presence of passengers smoking cigarettes.