Mobile Source Air Toxics Research Articles

Second-by-Second Characterization of Cold-Start Gas-Phase and Air Toxic Emissions from a Light-Duty Vehicle

Tailpipe pollutants from motor vehicles are linked to environmental concerns and human health issues. Gasoline engine ignition produces a significant portion of trip emissions, but few studies have quantified mobile source air toxic (MSAT) species for light-duty vehicles during cold start. Real-world tailpipe emissions were measured from a 1999 Toyota Sienna minivan with the University of Vermont total onboard tailpipe emissions measurement system. A Fourier transform infrared spectrometer measured 27 gas-phase emissions for cold start, extended idle, and warm-up driving at 1-s temporal resolution. Analysis demonstrated that (a) time to optimal function of emissions control devices was not indicated by one species, but varied for different pollutants; (b) extended idling after cold start produced elevated emissions for MSAT species as compared to warm-up driving; and (c) ambient temperatures ranging from 9.5°C to 38.4°C affected species from each emission category, with the exception of carbon dioxide. Carbon monoxide produced peak emissions three orders of magnitude higher than hot-stabilized conditions for an average of 90 s, regardless of operating conditions, while nitric oxide peak emissions were over an order of magnitude higher during warm-up driving than extended idle. Peak MSAT emissions, up to two orders of magnitude higher than hot-stabilized idle, were maintained or increased during extended idle and decreased to baseline within 100 to 200 s of warm-up driving. Results indicate extended idling after cold starts prolongs elevated concentrations of MSAT emissions, suggesting that recent policy efforts to reduce vehicle idling behavior could limit potential human exposure to the toxic exhaust constituents.

Mobile Source Air Toxic Emissions

This study used a new emissions modeling tool, CT-EMFAC, to assess the sensitivity of mobile source air toxic (MSAT) emissions to changes in traffic volumes, speeds, and fleet composition. In addition, the choice of the speed calculation method, which is usually part of a postprocessing technique, was analyzed. The investigation employed a hypothetical 6.7-mi freeway segment located in southern California; activity data were derived from comparable real-world information obtained from the California Department of Transportation. Results show that emissions more than doubled in 2004 and increased by a factor of two to four in 2030 when traffic volumes increased 30% above base case conditions. The nonlinear shift in emissions was a function of decreased travel speeds and increased grams per mile emission rates that accompanied increased traffic volumes. Fleet composition (the proportion of trucks) was also shown to affect MSAT emissions, especially for diesel particulate matter and aldehydes. Under some scenarios, the choice of the speed calculation method had a greater effect on MSAT emissions than 26 years of fleet turnover. The analysis also showed that the type of speed calculation method used could result in large variations in MSAT emissions. Application of one speed calculation method resulted in calculated congested freeway speeds that did not fall below 10 mph. The speed calculation method chosen was highly influential in the 2030 case study when forecasted volumes reached levels at which speeds approached the 10 mph minimum allowed by the speed calculation method; this probably underpredicted emissions.

High time-resolved measurements of organic air toxics in different source regimes

High time-resolved (HTR) measurements can provide significant insight into sources and exposures of air pollution. In this study, an automated instrument was developed and deployed to measure hourly concentrations of 18 gas-phase organic air toxics and 6 volatile organic compounds (VOCs) at three sites in and around Pittsburgh, Pennsylvania. The sites represent different source regimes: a site with substantial mobile-source emissions; a residential site adjacent to a heavily industrialized zone; and an urban background site. Despite the close proximity of the sites (less than 13 km apart), the temporal characteristic of outdoor concentrations varied widely. Most of the compounds measured were characterized by short periods of elevated concentrations or plume events, but the duration, magnitude and composition of these events varied from site to site. The HTR data underscored the strong role of emissions from local sources on exposure to most air toxics. Plume events contributed more than 50% of the study average concentrations for all pollutants except chloroform, 1,2-dichloroethane, and carbon tetrachloride. Wind directional dependence of air toxic concentrations revealed that emissions from large industrial facilities affected concentrations at all of the sites. Diurnal patterns and weekend/weekday variations indicated the effects of the mixing layer, point source emissions patterns, and mobile source air toxics (MSATs) on concentrations. Concentrations of many air toxics were temporally correlated, especially MSATs, indicating that they are likely co-emitted. It was also shown that correlations of the HTR data were greater than lower time resolution data (24-h measurements). This difference was most pronounced for the chlorinated pollutants. The stronger correlations in HTR measurements underscore their value for source apportionment studies.

Multi-criteria decision analysis for the selection of a near road ambient air monitoring site for the measurement of mobile source air toxics

In 2002, the Sierra Club legally challenged the US Federal Highway Administration and the Nevada Department of Transportation’s National Environmental Policy Act environmental document related to the proposed widening of US 95 in Las Vegas, Nevada, including the assessment of impacts of mobile source air toxics from the proposed project. To resolve the situation, Federal Highway Administration entered into a Settlement Agreement with Nevada DOT and the Sierra Club, wherein the Administration agreed to undertake a research effort to characterize the impact and behavior of particulate matter with aerodynamic diameter less than 2.5 μm and mobile source air toxics near highways. The US Federal Highway Administration and US Environmental Protection Agency determined that it would be in the best interest of both organizations to implement this project in a collaborative manner, allowing a more effective utilization of staffing and resources. One of the first steps of the project implementation has been the selection of a suitable ambient air monitoring site in or around Las Vegas, Nevada. This article presents the multi-criteria analytical steps taken to select the near road monitoring sites to provide air quality data needed to support environmental decision-making in this project.

Mobile Source Air Toxics (MSATs) from High Efficiency Clean Combustion: Catalytic Exhaust Treatment Effects

High Efficiency Clean Combustion (HECC) strategies such as homogenous charge compression ignition (HCCI) and pre-mixed charge compression ignition (PCCI) offer much promise for the reduction of NOx and PM from diesel engines. While delivering low PM and low NOx, these combustion modes often produce much higher levels of CO and HC than conventional diesel combustion modes. In addition, partially oxygenated species such as formaldehyde (an MSAT) and other aldehydes increase with HECC modes. The higher levels of CO and HCs have the potential to compromise the performance of the catalytic aftertreatment, specifically at low load operating points. As HECC strategies become incorporated into vehicle calibrations, manufacturers need to avoid producing MSATs in higher quantities than found in conventional combustion modes. This paper describes research on two different HECC strategies, HCCI and PCCI. Engine-out data for several MSAT species (formaldehyde, acetaldehyde, benzene, toluene, ethylbenzene, xylenes, naphthalene, PAHs, diesel PM) as well as other HC species are presented and compared when possible with conventional operation. In addition, catalyst-out values were measured to assess the destruction of individual MSATs over the catalyst. At low engine loads, MSATs were higher and catalyst performance was poorer. Particle sizing results identify large differences between PM frommore » conventional and HECC operation.« less

Innovative Technologies: Transportation Fuels on the Table

On 29–30 November 2007, just days before the United Nations Climate Change Conference began in Bali and Al Gore and Rajendra Pachauri received the 2007 Nobel Peace Prize for their work on climate change, the U.S. Institute of Medicine (IOM) held a workshop to highlight gaps in scientific understanding about the environmental and human health effects of transportation fuels. The transportation sector’s use of fuel is expected to grow more quickly than demand for energy in any other sector between 2005 and 2030, Scott Nauman, manager of economy and energy in the ExxonMobil Corporate Planning Department, told conference attendees. Therefore, new transportation fuels are key players among the innovative technologies being investigated and developed to help countries throughout the world cut greenhouse gas emissions. As worldwide transportation fuel use rises, the emissions and carbon dioxide emitted by burning these fuels will also rise, pointed out Samuel Wilson, acting director of the NIEHS. “We want to add ‘minimizing the human health impact’ . . . to the criteria for developing alternative fuels,” he said. According to Michael Wang, a vehicle and fuel systems analyst at the U.S. Department of Energy Argonne National Laboratory, biofuels are considered the most promising alternative for reducing petroleum use and decreasing greenhouse gas emissions from transportation. Electricity is also expected to grow as a source for plug-in hybrids, as is hydrogen. The idea of producing transportation fuels from coals “has generated some interest lately because they can be produced domestically,” Wang says, but their carbon emissions are “pretty high.” The main biofuel currently being developed for transportation in the United States is ethanol from corn via distillation, and its production is increasing rapidly. According to the Energy Information Administration, the percentage of the U.S. gasoline pool represented by ethanol rose from 1.27% in 2000 to 2.85% in 2005. However, John Regalbuto, director of the National Science Foundation’s Catalysis and Biocatalysis Program, predicts that hydrocarbon-based “green gasoline,” “green diesel,” and “green jet fuel” will represent a significant fraction of new biofuels by 2022. When produced via catalysis from materials such as switch-grass and waste wood products, the performance of these renewable biofuels are “essentially the same” as their conventional counterparts, he says. However, their manufacture involves intermediates such as hydroxymethylfurfural and ionic liquid solvents that require further study in terms of health effects. Additives also affect the emissions of transportation fuels, as well as these fuels’ impact on the environment, stressed Serap Erdal, an assistant professor at the University of Illinois–Chicago School of Public Health. Uncertainty over which additives will be added to new fuels and how the complex mixtures will behave in the environment makes it very hard to predict potential health effects, agreed the experts amassed at the IOM meeting. In the United States, for example, ethanol has only recently been used as an additive to make gasoline burn more efficiently. But in Brazil, where ethanol has been used as a fuel for nearly 30 years, it has become clear that, compared with gasoline, the sugarcane-derived fuel produces much higher emissions of formaldehyde, a known human carcinogen, and acetylaldehyde, a suspected human carcinogen, said Paolo Saldiva, a professor of medicine in the University of Sao Paolo’s Department of Pathology. However, he said that the health effects of exposure to these compounds via air emissions are unclear. What is indisputable is that key decisions leading to the development of new fuels will be made before the requisite health effects data are available, so “we need to get going as soon as possible . . . to collect baseline data,” said Dan Greenbaum, president of the Health Effects Institute, which published a report summarizing the health effects of exposure to 21 mobile source air toxics in November 2007. Added Erdal, “There is a critical need to institute public health surveillance so that we are already collecting data and are able to detect changes as they take place.”

Inhalation exposure and risk from mobile source air toxics in future years

Modeling of inhalation exposure and risks resulting from exposure to mobile source air toxics can be used to evaluate impacts of reductions from control programs on overall risk, as well as changes in relative contributions of different source sectors to risk, changes in contributions of different pollutants to overall risk, and changes in geographic distributions of risk. Such analysis is useful in setting regulatory priorities, and informing the decision-making process. In this paper, we have conducted national-scale air quality, exposure, and risk modeling for the US in the years 2015, 2020, and 2030, using similar tools and methods as the 1999 National-Scale Air Toxics Assessment. Our results suggest that US Environmental Protection Agency emission control programs will substantially reduce average inhalation cancer risks and potential noncancer health risks from exposure to mobile source air toxics. However, cancer risk and noncancer hazard due to inhalation of air toxics will continue to be a public health concern.

Methodology for Evaluating Mobile Source Air Toxic Emissions

With the final update to its on-road mobile source emission factor model, MOBILE6.2, the U.S. Environmental Protection Agency (EPA) added capabilities for predicting emissions factors for a select group of mobile source air toxics (MSATs), commonly referred to as the six priority MSATs. These are acetaldehyde, acrolein, benzene, 1,3-butadiene, diesel particulate matter, and formaldehyde. This paper describes a methodology for computing and evaluating emissions of MSATs among a group of transportation project alternatives. When the future options for upgrading a transportation corridor are evaluated, the major mitigating factor in reducing MSAT emissions is the implementation of EPA's new motor vehicle emission control standards. Substantial decreases in MSAT emissions will be realized from a current base year through an estimated time of completion for a planned upgrading project and its design year some 25 years in the future. Even when anticipated increases in vehicle miles of travel and varying degrees of efficiency of vehicle operation are accounted for, total MSAT emissions are predicted to decline more than 61% from 2005 to 2030. Although benzene emissions are predicted to decline more than 35%, emissions of diesel particulate matter are predicted to decline considerably more (i.e., >92%). The ability to discern remarkable differences in MSAT emissions among transportation alternatives is difficult, given the uncertainties associated with the forecasting of travel activity and air emissions 25 years or more into the future. In this hypothetical congestion mitigation project, differences in MSAT emissions between the build and no-action alternatives range from more than 6% to less than 16%.

Methodology for Evaluating Mobile Source Air Toxic Emissions: Transportation Project Alternatives

With the final update to its on-road mobile source emission factor model, MOBILE6.2, the U.S. Environmental Protection Agency (EPA) added capabilities for predicting emissions factors for a select group of mobile source air toxics (MSATs), commonly referred to as the six priority MSATs. These are acetaldehyde, acrolein, benzene, 1, 3-butadiene, diesel particulate matter, and formaldehyde. This paper describes a methodology for computing and evaluating emissions of MSATs among a group of transportation project alternatives. When the future options for upgrading a transportation corridor are evaluated, the major mitigating factor in reducing MSAT emissions is the implementation of EPA's new motor vehicle emission control standards. Substantial decreases in MSAT emissions will be realized from a current base year through an estimated time of completion for a planned upgrading project and its design year some 25 years in the future. Even when anticipated increases in vehicle miles of travel and varying degree...

Variability of Mobile Source Air Toxic Emissions Factors with MOBILE6.2

This paper documents the ranges of mobile source air toxic (MSAT) emissions factors produced by the U.S. Environmental Protection Agency's MOBILE6.2 model because of changes in a variety of input parameters. These include calendar year, ambient temperature, fuel (gasoline) Reid vapor pressure (RVP), and vehicle speed. The variability of MSAT emissions factors is more than an order of magnitude. They are the most sensitive to changes in calendar year. For hydrocarbon-based MSATs (i.e., acetaldehyde, acrolein, benzene, butadiene, and formaldehyde), significant decreases in emissions factors can be realized by mitigating congested vehicle speeds. The variability is less for changes in temperature and changes in fuel RVP with moderate temperature. The emissions factors for diesel particulate matter change only as a function of calendar year and are not sensitive to changes in vehicle speed, temperature, or fuel RVP.

Variability of Mobile Source Air Toxic Emissions Factors with MOBILE6.2

This paper documents the ranges of mobile source air toxic (MSAT) emissions factors produced by the U.S. Environmental Protection Agency's MOBILE6.2 model because of changes in a variety of input parameters. These include calendar year, ambient temperature, fuel (gasoline) Reid vapor pressure (RVP), and vehicle speed. The variability of MSAT emissions factors is more than an order of magnitude. They are the most sensitive to changes in calendar year. For hydrocarbon-based MSATs (i.e., acetaldehyde, acrolein, benzene, butadiene, and formaldehyde), significant decreases in emissions factors can be realized by mitigating congested vehicle speeds. The variability is less for changes in temperature and changes in fuel RVP with moderate temperature. The emissions factors for diesel particulate matter change only as a function of calendar year and are not sensitive to changes in vehicle speed, temperature, or fuel RVP.

The mobile source air toxics rule : How does the greatest reduction become no reduction?

The mobile source air toxics rule : How does the greatest reduction become no reduction?