Mobile Source Air Toxics Research Articles

Methodology for Mobile Toxics Deterministic Human Health Risk Assessment and Case Study

Air toxic emissions from on-road mobile sources are significant contributors to the degradation of air quality in urban and dense population centers. Research led by the United States Environmental Protection Agency (EPA) identified more than 1162 hazardous air pollutants (HAPs) in the exhaust and evaporative emissions from on-road mobile sources. However, less than 70 hazardous air pollutants are monitored by regulatory agencies. HAPs emitted from Mobile Sources are known as Mobile Source Air Toxics (MSATs). The EPA estimates that approximately half of the cancer risk and 74% of noncancer health impacts from air toxics is attributed to mobile sources. The quantification of the risk associated with MSATs exposure remains limited to date, and only a few MSATs have ambient air quality standards to protect human health and welfare. This work presents a novel and validated methodology to quantify the myriad health risks associated with exposure to on-road mobile emissions. This methodology is introduced in the form of a pipelined analysis process, which may be employed in existing and new transportation projects. The proposed new methodology integrates results from three different types of models: on-road vehicle emissions inventory models such as MOVES and IVE, air dispersion models such as AERMOD and SCIPUFF, and risk estimate models for human and ecological receptors such as the 2005 Final U.S. EPA Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities. The result of this research work is a new methodology that provides regulators and risk analysts with a more detailed awareness of the health impacts of MSATs. A case study of Saint Paul, Minnesota, validated the air dispersion modeled results against monitored data, and the agreement was acceptable (i.e., the estimates were within a factor of two of the observations). Three high-population locations in the Saint Paul area were evaluated for human health risk, with the observation that at two of these locations, the Saint Paul—Ramsey Health Center and Anderson Office Building, the calculated cancer risk is in excess of the target risk level of 1.0E-05 for benzo(a)pyrene. The methodology presented in this paper allows regulators, risk analysts, and air quality engineers to better estimate multi-pathway cancer and noncancer risk associated with acute and chronic exposure to MSATs. Moreover, this work provides a science-based aid to policy decision makers when considering factors that most significantly affect population health and ecology.

Mobile Source Benzene Regulations and Risk of Childhood and Young Adult Hematologic Cancers in Alaska: A Quasi-experimental Study.

We aimed to evaluate the impact of the EPA's Mobile Source Air Toxics rules (MSAT), which targeted benzene emissions, on childhood and young adult leukemia and lymphoma incidence in Alaska. MSAT was implemented in 2011 and produced a dramatic decline in ambient benzene in Alaska. Due to previous benzene-related regulations enacted in the continental United States, MSAT had relatively modest impacts in other states. This created quasi-experimental conditions leveraged in this study. Using 2-year state-level incidence rates of childhood and young adult leukemia and lymphoma for each US state 2001-2018, we examined MSAT-attributable changes in incidence by applying a difference-in-differences approach. We found evidence of a substantial reduction associated with MSAT in incidence of childhood and young adult lymphoma (-1.23 [-1.84, -0.62] cases per 100,000), but not in leukemia (-0.13 [-0.77, 0.51] cases per 100,000). Our findings are consistent with the hypothesis that MSAT, which reduced benzene levels in Alaska, led to a decline in lymphoma incidence in children and young adults.

Editorial: Reducing Daily Exposure to Mobile Source Air Toxics by Improving Vehicle Cabin Air Quality

Editorial: Reducing Daily Exposure to Mobile Source Air Toxics by Improving Vehicle Cabin Air Quality

Assessment of mobile source air toxics in an Environmental Justice Denver community adjacent to a freeway

ABSTRACT Air pollutant concentrations are often higher near major roadways than in the surrounding environments owing to emissions from on-road mobile sources. In this study, we quantified the gradient in black carbon (BC) and air toxics concentrations from the I-70 freeway in the Elyria-Swansea environmental justice neighborhood in Denver, Colorado, during three measurement campaigns in 2017–2018. The average hourly upwind-downwind gradient of BC concentrations from the roadway was 500–800 ng/m3, equal to an increment of approximately 30-80% above local background levels within 180 m of the freeway. When integrated over all wind directions, the gradients were smaller, approximately 150–300 ng/m3 (~11-18%) over the course of nearly four months of measurements. No statistically significant gradient in air toxics (e.g., benzene, formaldehyde, etc.) was found, likely because the uncertainties in the mean concentrations were larger than the magnitude of the gradient (<25%). This finding is in contrast to some earlier studies in which small gradients of benzene and other VOCs were found. We estimate that sample sizes of at least 100 individual measurements would have been required to estimate mean concentrations with sufficient certainty to quantify gradients on the order of ±10% uncertainty. These gradient estimates are smaller than those found in previous studies over the past two decades; more stringent emissions standards, the local fleet age distribution, and/or the steady turnover of the vehicle fleet may be reducing the overall impact of roadway emissions on near-road communities. Implications: Gradients of near-road pollution may be declining in the near-road environment as tailpipe emissions from the vehicle fleet continue to decrease. Near-road concentration gradients of mobile source air toxics, including benzene, 1,3-butadiene, and ethylbenzene, will require higher sample sizes to quantify as emissions continue to decline.

Investigation of the Effect of Mid- And High-Level Ethanol Blends on the Particulate and the Mobile Source Air Toxic Emissions from a Gasoline Direct Injection Flex Fuel Vehicle

This study examined the influence of low-, mid-, and high-ethanol fueling, as well as the influence of the aromatic hydrocarbons in the fuel blend, on the regulated and greenhouse gas emissions, the mobile source air toxic pollutants, and the particulate emissions from a current model flexible fuel vehicle equipped with a gasoline direct injection engine. This study utilized a total of four fuels, including a baseline U.S. EPA Tier 3 E10 fuel, one E10 fuel with higher aromatics content than the baseline E10, an E30 fuel that was splash-blended with the Tier 3 E10, and an E78 fuel. Testing was conducted over triplicate cold-start and hot-start LA92 cycles. The findings of this study showed that the higher ethanol blends, namely, the E30 and E78, led to statistically significant reductions of 9%–13% for total hydrocarbon (THC), 13%–44% for non-methane hydrocarbon (NMHC), 20%–35% for carbon monoxide (CO), and 17%–36% for nitrogen oxides (NOx) emissions compared to the high-aromatics E10 fuel. The emissions o...

Effect of Ambient Temperature on Total Organic Gas Speciation Profiles from Light-Duty Gasoline Vehicle Exhaust.

Total organic gases (TOG) emissions from motor vehicles include air toxic compounds and contribute to formation of ground-level ozone and secondary organic aerosol (SOA). These emissions are known to be affected by temperature; however previous studies have typically focused only on the temperature dependence of total emission factors and select toxic compounds. This study builds on the previous research by performing an evaluation of a comprehensive set of gas-phase organic compounds present in gasoline motor vehicle exhaust. A fleet of five vehicles using port fuel injection engine technology and running on E10 fuel was tested. Overall, three temperatures (0, 20, and 75 °F; or -18, -7, and 24 °C), two driving conditions (urban-FTP75 and aggressive driving-US06) and 161 compounds were evaluated; the emissions distributions were used to construct speciation profiles for each driving cycle and temperature. Overall, the speciation results indicated a significant increase in alkane and methane content, and decrease in alcohol, aldehyde and ketone content with decreasing temperature. These were verified using a statistical significance test. The fraction and composition of Mobile Source Air Toxics (MSATs) were significantly affected by temperature for both driving cycles. The ozone forming potentials of these profiles were evaluated using the maximum incremental reactivity (MIR) scale. Aromatic content was predicted to be a major driver behind the ozone forming potentials. Additionally, the decreasing ozone potential could be attributed to increased methane fractions with increasing temperature.

Biofuels, vehicle emissions, and urban air quality.

Increased biofuel content in automotive fuels impacts vehicle tailpipe emissions via two mechanisms: fuel chemistry and engine calibration. Fuel chemistry effects are generally well recognized, while engine calibration effects are not. It is important that investigations of the impact of biofuels on vehicle emissions consider the impact of engine calibration effects and are conducted using vehicles designed to operate using such fuels. We report the results of emission measurements from a Ford F-350 fueled with either fossil diesel or a biodiesel surrogate (butyl nonanoate) and demonstrate the critical influence of engine calibration on NOx emissions. Using the production calibration the emissions of NOx were higher with the biodiesel fuel. Using an adjusted calibration (maintaining equivalent exhaust oxygen concentration to that of the fossil diesel at the same conditions by adjusting injected fuel quantities) the emissions of NOx were unchanged, or lower, with biodiesel fuel. For ethanol, a review of the literature data addressing the impact of ethanol blend levels (E0-E85) on emissions from gasoline light-duty vehicles in the U.S. is presented. The available data suggest that emissions of NOx, non-methane hydrocarbons, particulate matter (PM), and mobile source air toxics (compounds known, or suspected, to cause serious health impacts) from modern gasoline and diesel vehicles are not adversely affected by increased biofuel content over the range for which the vehicles are designed to operate. Future increases in biofuel content when accomplished in concert with changes in engine design and calibration for new vehicles should not result in problematic increases in emissions impacting urban air quality and may in fact facilitate future required emissions reductions. A systems perspective (fuel and vehicle) is needed to fully understand, and optimize, the benefits of biofuels when blended into gasoline and diesel.

Estimation of exhaust and non-exhaust gaseous, particulate matter and air toxics emissions from on-road vehicles in Delhi

Abstract Analysis of emissions from on-road vehicles in an Indian megacity, Delhi, have been performed by comparing exhaust emissions of gaseous, particulate matter and mobile source air toxics (MSATs), together with volatile organic compound (VOCs) and PM 10 (particulate matter ≤10 μm) from non-exhaust vehicular sources, during the past (1991–2011) and future (2011–2020) scenarios. Results indicate that emissions of most of the pollutants from private vehicles (two wheelers and cars) have increased by 2- to 18-times in 2020 over the 1991 levels. Two wheelers found to be dominating the emissions of carbon monoxide (CO, 29–51%), hydrocarbons (HC, 45–73%), acetaldehyde (46–51%) and total poly aromatic hydrocarbons (PAHs, 37–42%). Conversely, private cars were found to be responsible for the majority of the carbon dioxide (CO 2, 24–42%), 1,3-butadiene (72–89%), benzene (60–82%), formaldehyde (23–44%) and total aldehyde (27–52%) between 1991 and 2011. The heavy-duty commercial vehicles (HCVs) shows their accountability for most of the nitrogen oxide (NO x , 18–41%) and PM 10 (33–43%) emissions during the years 1991–2011. In terms of PM 10 emissions, vehicular exhaust contributed by 21–55%, followed by road dust (42–73%) and brake wear (3–5%) between 1991 and 2011. After 2002, non-exhaust emissions (e.g. road dust, brake wear and tyre wear) together indicate higher accountability (66–86%) for PM 10 emission than the exhaust emissions (14–34%). The temporal trend of emissions of NO x and CO show reasonable agreement with available ambient air concentrations that were monitored at locations, significantly influenced by vehicular activity. Encouraging results were emerged, showing a good correlation coefficient for CO (0.94) and NO x (0.68).

Effects of Cold Temperature and Ethanol Content on VOC Emissions from Light-Duty Gasoline Vehicles.

Emissions of speciated volatile organic compounds (VOCs), including mobile source air toxics (MSATs), were measured in vehicle exhaust from three light-duty spark ignition vehicles operating on summer and winter grade gasoline (E0) and ethanol blended (E10 and E85) fuels. Vehicle testing was conducted using a three-phase LA92 driving cycle in a temperature-controlled chassis dynamometer at two ambient temperatures (-7 and 24 °C). The cold start driving phase and cold ambient temperature increased VOC and MSAT emissions up to several orders of magnitude compared to emissions during other vehicle operation phases and warm ambient temperature testing, respectively. As a result, calculated ozone formation potentials (OFPs) were 7 to 21 times greater for the cold starts during cold temperature tests than comparable warm temperature tests. The use of E85 fuel generally led to substantial reductions in hydrocarbons and increases in oxygenates such as ethanol and acetaldehyde compared to E0 and E10 fuels. However, at the same ambient temperature, the VOC emissions from the E0 and E10 fuels and OFPs from all fuels were not significantly different. Cold temperature effects on cold start MSAT emissions varied by individual MSAT compound, but were consistent over a range of modern spark ignition vehicles.

High-end exposure relationships of volatile air toxics and carbon monoxide to community-scale air monitoring stations in Atlanta, Chicago, and Houston.

Evaporative and exhaust mobile source air toxic (MSAT) emissions of total volatile organic compounds, carbon monoxide, BTEX (benzene, toluene, ethylbenzene, and xylenes), formaldehyde, acetaldehyde, butadiene, methyl tertiary butyl ether, and ethanol were measured in vehicle-related high-end microenvironments (ME) under worst-case conditions plausibly simulating the >99th percentile of inhalation exposure concentrations in Atlanta (baseline gasoline), Chicago (ethanol-oxygenated gasoline), and Houston (methyl tertiary butyl either-oxygenated gasoline) during winter and summer seasons. High-end MSAT values as ratios of the corresponding measurements at nearby air monitoring stations exceeded the microenvironmental proximity factors used in regulatory exposure models, especially for refueling operations and MEs under reduced ventilation. MSAT concentrations were apportioned between exhaust and evaporative vehicle emissions in Houston where methyl tertiary butyl ether could be used as a vehicle emission tracer. With the exception of vehicle refueling operations, the results indicate that evaporative emissions are a minor component of high-end MSAT exposure concentrations.

Impact of emissions from natural gas production facilities on ambient air quality in the Barnett Shale area: A pilot study

Rapid and extensive development of shale gas resources in the Barnett Shale region of Texas in recent years has created concerns about potential environmental impacts on water and air quality. The purpose of this study was to provide a better understanding of the potential contributions of emissions from gas production operations to population exposure to air toxics in the Barnett Shale region. This goal was approached using a combination of chemical characterization of the volatile organic compound (VOC) emissions from active wells, saturation monitoring for gaseous and particulate pollutants in a residential community located near active gas/oil extraction and processing facilities, source apportionment of VOCs measured in the community using the Chemical Mass Balance (CMB) receptor model, and direct measurements of the pollutant gradient downwind of a gas well with high VOC emissions. Overall, the study results indicate that air quality impacts due to individual gas wells and compressor stations are not likely to be discernible beyond a distance of approximately 100 m in the downwind direction. However, source apportionment results indicate a significant contribution to regional VOCs from gas production sources, particularly for lower-molecular-weight alkanes (<C6). Although measured ambient VOC concentrations were well below health-based safe exposure levels, the existence of urban-level mean concentrations of benzene and other mobile source air toxics combined with soot to total carbon ratios that were high for an area with little residential or commercial development may be indicative of the impact of increased heavy-duty vehicle traffic related to gas productionImplicationsRapid and extensive development of shale gas resources in recent years has created concerns about potential environmental impacts on water and air quality. This study focused on directly measuring the ambient air pollutant levels occurring at residential properties located near natural gas extraction and processing facilities, and estimating the relative contributions from gas production and motor vehicle emissions to ambient VOC concentrations. Although only a small-scale case study, the results may be useful for guidance in planning future ambient air quality studies and human exposure estimates in areas of intensive shale gas production.

Analysis of mobile source air toxics (MSATs)—Near-road VOC and carbonyl concentrations

Exposures to mobile source air toxics (MSATs) have been associated with numerous adverse health effects. While thousands of air toxic compounds are emitted from mobile sources, members of a subset of compounds are considered high priority due to their significant contribution to cancer and noncancer health risks and the contribution of mobile sources to total exposure as evaluated by the U.S. Environmental Protection Agency (EPA) National-Scale Air Toxics Assessments (NATA). These pollutants include benzene, 1,3-butadiene, ethylbenzene, acrolein, acetaldehyde, formaldehyde, naphthalene, polycyclic organic matter, and diesel particulate matter/organic gases. This study provided year-long trends of benzene, 1,3-butadiene, acrolein, acetaldehyde, and formaldehyde in Las Vegas, NV. Results indicated that MSAT concentrations often did not exhibit trends typical of other primary emitted pollutants in this study. Instead, other mobile sources beyond the highway of interest contributed to the measured values, including a major arterial road, a large commercial airport, and a nearby parking lot. The data were compared with relevant census-tract NATA estimates, with estimated ambient 1,3-butadiene concentrations similar to the measured values. Measured benzene values were much lower relative to the NATA total ambient benzene concentrations. Measured acrolein values were much higher relative to the NATA total acrolein concentrations. Measured acetaldehyde and formaldehyde values were also higher relative to the NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions. Some possible explanations for these differences include nearby sources influencing the measured values; meteorological influences that may not be well captured by the NATA modeling regime; chemical reactivity of measured compounds; and additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions. Implications: Comparison of air toxics concentrations measured at four long-term near-road sites in Las Vegas, NV, show generally good agreement with the EPA 2005 NATA total ambient concentrations. Measured concentrations did not compare as well with EPA 2005 NATA for the on-road mobile portion of the ambient concentrations. This highlights the complexity of air toxic emission sources and impacts in urban areas, especially around large highway facilities; NATA's inability to capture local-scale meteorology and fine-scale ambient gradients; and that additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions.

Concentrations of mobile source air pollutants in urban microenvironments

Human exposures to criteria and hazardous air pollutants (HAPs) in urban areas vary greatly due to temporal-spatial variations in emissions, changing meteorology, varying proximity to sources, as well as due to building, vehicle, and other environmental characteristics that influence the amounts of ambient pollutants that penetrate or infiltrate into these microenvironments. Consequently, the exposure estimates derived from central-site ambient measurements are uncertain and tend to underestimate actual exposures. The Exposure Classification Project (ECP) was conducted to measure pollutant concentrations for common urban microenvironments (MEs) for use in evaluating the results of regulatory human exposure models. Nearly 500 sets of measurements were made in three Los Angeles County communities during fall 2008, winter 2009, and summer 2009. MEs included in-vehicle, near-road, outdoor, and indoor locations accessible to the general public. Contemporaneous 1- to 15-min average personal breathing zone concentrations of carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs), nitric oxide (NO), nitrogen oxides (NOx), particulate matter (<2.5 μm diameter; PM2.5) mass, ultrafine particle (UFP; <100 nm diameter) number, black carbon (BC), speciated HAPs (e.g., benzene, toluene, ethylbenzene, xylenes [BTEX], 1,3-butadiene), and ozone (O3) were measured continuously. In-vehicle and inside/outside measurements were made in various passenger vehicle types and in public buildings to estimate penetration or infiltration factors. A large fraction of the observed pollutant concentrations for on-road MEs, especially near diesel trucks, was unrelated to ambient measurements at nearby monitors. Comparisons of ME concentrations estimated using the median ME/ambient ratio versus regression slopes and intercepts indicate that the regression approach may be more accurate for on-road MEs. Ranges in the ME/ambient ratios among ME categories were generally greater than differences among the three communities for the same ME category, suggesting that the ME proximity factors may be more broadly applicable to urban MEs.Implications:Estimates of population exposure to air pollutants extrapolated from ambient measurements at ambient fixed site monitors or exposure surrogates are prone to uncertainty. This study measured concentrations of mobile source air toxics (MSAT) and related criteria pollutants within in-vehicle, outdoor near-road, and indoor urban MEs to provide multipollutant ME measurements that can be used to calibrate regulatory exposure models.

Modeling Concentrations of Air Toxics near Intersections and Freeways in Florida

AbstractThis paper reports on the results of dispersion modeling of mobile source air toxics (MSATs) near seven intersections and seven freeway segments in the state of Florida. Different modeling approaches were used, all with the focus on a hot-spot analysis to obtain the worst-case (highest) 1-h concentration. To accomplish the worst-case modeling, the CAL3QHC model was modified to handle inputs of several individual MSATs and to predict the concentrations of these MSATs around roadways. Real-world data (traffic volumes and site geometry) were gathered, meteorological input data were selected, and mobile source emission factors (EFs) were obtained from the U.S. EPA’s mobile-source emissions model, MOVES2010a. Based on a literature search of short-term effects, maximum acceptable concentrations (MACs) for a 1-h averaging time were proposed for comparison with the modeled results. Results from this study indicate that for all of the intersections and freeway segments, the worst-case 1-h modeled concentra...

Mobile source air toxic emissions from direct injection spark ignition gasoline and LPG passenger car under various in-use vehicle driving modes in Korea

Mobile source air toxic (MSAT) emissions from a direct injection spark ignition (DISI) passenger vehicle fueled with gasoline and liquid phase liquefied petroleum gas (LPG) were compared using a chassis dynamometer under several in-use vehicle driving conditions. For operation of a dedicated LPG-DI engine, low-pressure fuel systems were specially installed and various engine control parameters were recalibrated considering different chemical properties of LPG. A series of the National Institute of Environmental Research (NIER) modes for determining the emission factors of in-use vehicles in Korea were chosen to quantify not only the regulated emissions with particles but also the unregulated emissions of carbonyls, BTEX, and PAHs from a DISI light-duty vehicle (LDV) with gasoline and LPG. The regulated and particle emissions of LPG-DI vehicles showed strong reduction, and the proportions of sub-23nm particles were 32–35% in gasoline and 50–65% in LPG. The results revealed that the levels of the MSAT emissions from a DISI engine were closely related to the driving patterns and the fuel properties. A substantial reduction of regulated emissions, particulates, BTEX, and particle-bound PAH emissions was achieved from a LPG-DI vehicle in real driving conditions. Carbonyl compounds acetaldehyde and acrolein showed significant increment from a LPG-DI vehicle.

Emission Scenarios and the Health Risks Posed by Priority Mobile Air Toxics in an Urban to Regional Area: An Application in Nashville, Tennessee

Toxic air pollutants, also known as hazardous air pollutants, are those that are known or suspected to cause cancer or other serious health effects, such as birth defects or adverse environmental outcomes. The aim of this research was to predict air toxics related health risks due to different emission scenarios by linking Models-3/CMAQ and cancer risk assessments. To demonstrate the effectiveness of this approach, this study was performed on the priority mobile source air toxics (PMSAT) of benzene, 1,3-butadiene, formaldehyde, acetaldehyde, and diesel particulate matter (DPM), based on data from 2003. The analysis was carried out in the eastern US, and mainly in Nashville, TN. Ten emissions scenarios were examined, including a 2020 scenario with the effects of on-road mobile source regulations. The results show that DPM poses a cancer risk that is 4.2 times higher than the combined total cancer risk from all of four other PMSAT. These high cancer risk levels are mainly due to non-road sources (57.9%). The main cancer risk from acetaldehyde, benzene, formaldehyde, and 1,3-butadiene (4HAPs) is due to biogenic sources, which account for 32.2% of this risk, although these cannot be controlled. Excluding DPM, the main on-road cancer risk contribution was due to the air toxics generated by gasoline light duty vehicles (LDVs), principally benzene and 1,3-butadiene. The scenario for 2020 showed reductions in the adverse health effects related to DPM and 4HAPs of 32.8 and 19.4%, respectively. This research provides strong evidence that reducing ambient DPM concentrations will lead to greater improvements in human health than other air toxics, indicating that better technologies and regulations must be applied to mobile diesel engines, as these have more significant adverse health effects than non-road diesel sources.

Real-Time Measurement of Trace Air Toxic Vehicular Emissions by REMPI-TOFMS during Dynamometer Driving Cycles

Real time measurements of air toxic emissions were made from vehicles undergoing transient cycles on a dynamometer. Resonance-enhanced multi-photon ionization (REMPI) with time of flight mass spectrometry (TOFMS) was used to characterize rapid responses in trace aromatic emissions, including mobile source air toxics, to changes in driving cycles. Concurrent sampling of PM, CO, and CO2, with vehicle parameters of horsepower, velocity, and total particle density allowed the air toxic emissions to be related to operating performance. Two models of the U.S. Army High Mobility Multi-purpose Wheeled Vehicle (HMMWV), a diesel (M1097) and a turbocharged diesel version (M1114), were tested. Emissions were measured while running on a dynamometer-based roadway simulator under the West Virginia and EPA Federal Highway Economy Test cycles and under steady state, constant velocity conditions. Emission factors were determined for criteria pollutants such as CO and CO2, as well as for aromatic air toxics including benzene, toluene, ethylbenzene, and xylenes, as well as small polycyclic aromatic hydrocarbons such as naphthalene and methylnaphthalene. The combined dynamometer cycle and REMPI-TOFMS system relative accuracy (triplicate) varied from 15% to 79% for benzene, 31% to 109% for naphthalene, and 47% to 214% for 2-methylnaphthalene. CO and CO2 emissions were found to poorly correlate with benzene, naphthalene, and 2-methylnaphthalene. The fast time response of REMPI-TOFMS documented the compound-specific trace concentrations during cold startups of the M1097, showing benzene at ~230 ppb but then rapidly (within 60 s) tailing off to a steady state level around 50 ppb. This work highlights the ability of REMPI-TOFMS to measure trace air toxics in real time, following rapid changes in emissions during roadway cycles that cannot be identified using typical long term (minutes) integrated sampling methods.

Real-Time Measurement of Trace Air Toxic Vehicular Emissions by REMPI-TOFMS during Dynamometer Driving Cycles

Real time measurements of air toxic emissions were made from vehicles undergoing transient cycles on a dynamometer. Resonance-enhanced multi-photon ionization (REMPI) with time of flight mass spectrometry (TOFMS) was used to characterize rapid responses in trace aromatic emissions, including mobile source air toxics, to changes in driving cycles. Concurrent sampling of PM, CO, and CO2, with vehicle parameters of horsepower, velocity, and total particle density allowed the air toxic emissions to be related to operating performance. Two models of the U.S. Army High Mobility Multi-purpose Wheeled Vehicle (HMMWV), a diesel (M1097) and a turbocharged diesel version (M1114), were tested. Emissions were measured while running on a dynamometer-based roadway simulator under the West Virginia and EPA Federal Highway Economy Test cycles and under steady state, constant velocity conditions. Emission factors were determined for criteria pollutants such as CO and CO2, as well as for aromatic air toxics including benzene, toluene, ethylbenzene, and xylenes, as well as small polycyclic aromatic hydrocarbons such as naphthalene and methylnaphthalene. The combined dynamometer cycle and REMPI-TOFMS system relative accuracy (triplicate) varied from 15% to 79% for benzene, 31% to 109% for naphthalene, and 47% to 214% for 2-methylnaphthalene. CO and CO2 emissions were found to poorly correlate with benzene, naphthalene, and 2-methylnaphthalene. The fast time response of REMPI-TOFMS documented the compound-specific trace concentrations during cold startups of the M1097, showing benzene at ~230 ppb but then rapidly (within 60 s) tailing off to a steady state level around 50 ppb. This work highlights the ability of REMPI-TOFMS to measure trace air toxics in real time, following rapid changes in emissions during roadway cycles that cannot be identified using typical long term (minutes) integrated sampling methods.

Quantification of personal exposure concentrations to gasoline vehicle emissions in high-end exposure microenvironments: Effects of fuel and season

Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) with numerous emission sources of vehicle exhaust or evaporative emissions or during high-load and cold-start conditions. Reformulated fuels are expected to reduce MSAT and ozone precursor emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using reformulated (methyl tertiary-butyl ether [MTBE] or ethanol [EtOH]) fuels and conventional gasoline blends. The study investigates 13 high-end MEs, sampling under enhanced exposure conditions expected to result in maximal fuel and exhaust component exposures to carbon monoxide (CO), carbon dioxide (CO2), BTEX (benzene, toluene, ethylbenzene, xylenes), MTBE, 1,3-butadiene (1,3-BD), EtOH, formaldehyde (HCHO), and acetaldehyde (CH3CHO). The authors found that day-to-day ME variations in high-end benzene, 1,3-BD, HCHO, and CO concentrations are substantial, but independent of gasoline composition and season, and related to the activity and emission rates of ME sources, which differ from day to day. Implications: Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) in the presence of vehicular exhaust or evaporative emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using oxygenated (methyl tertiary-butyl ether or ethanol) and conventional gasoline blends. Personal exposure concentrations were quantified in selected MEs representing the upper end of the frequency distribution of potential population exposures. This work presents the first systematic look at high-end/maximal exposures to multiple contaminants, in multiple microenvironments, in multiple cities, over two seasons, for multiple fuels, making it a very complete evaluation of reformulated fuel impacts on MSAT concentrations in confined microenvironments. The study found that day-to-day ME variations of high-end pollutant concentrations are substantial, but independent of gasoline composition and season, and related to the variable daily activity and emission rates of ME sources. The data collected in this study may be used in bounding exposure modeling estimates that account for time spent in similar confining MEs. Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for information on average, maximum and minimum ME concentrations and summary of reconstructed 1-minute data.

Relationships of attached garage and home exposures to fuel type and emission levels of garage sources

Mobile source air toxics (MSAT) may pose an adverse health risk, especially in microenvironments with high exposures to vehicle exhaust or evaporative emissions. Although programs such as reformulated gasoline are intended to reduce the emissions of MSAT and ozone precursors, uncertainties remain regarding population exposures associated with both oxygenate-gasoline blends and conventional gasoline. Measurements were carried out in San Antonio, Texas under controlled conditions to establish relationships between vehicle tailpipe and evaporative emissions and concentration levels in a residence with an attached garage. This paper concentrates on the influence of vehicle type (sedan versus pickup truck), its operational mode (normal versus malfunction), and fuel type (conventional versus oxygenated) on the pollutant levels in the attached garage and adjacent room (kitchen).