Automobile emission limits

An example of a set of emission limits based on the rollback approach is the limits adopted by the United States for carbon monoxide, hydrocarbons, and oxides of nitrogen emissions from new automobiles (Table 25-2). 

Emission Limits Adopted by the United States for New Light-Duty Automobiles... 

The importance of lowering automobile emissions has already resulted in changes in car manufacturing. Electric cars, which were popular 100 years ago but fell by the wayside because they could not keep up with gasoline-powered cars, are making a comeback. Although battery-powered vehicles are useful for short, slow trips aroimd a crowded campus, for instance, they continue to be plagued by limited speeds and durations. Automobile manufacturers have alleviated these problems by com-... 

The Maximum Achievable Control Technology (MACT) emission limitations required by the 1990 Clean Air Act Amendments (CAAA) show the ultimate effect of the ratcheting process. After a little more than two decades of ratcheting, MWCs have become a comparatively minor source of combustion-related air pollution. Other artificial and natural sources such as automobiles, trucks, power plants, fireplaces, wood stoves, metal production furnaces, industrial manufacturing processes, volcanoes, forest fires, and backyard trash burning are now the major known sources of combustion-related pollutants. 

Rhodium compounds are somewhat toxic and have been used in oncological chemotherapy, but they are less effective than platinum complexes. The expense and rarity of rhodium means that it is rarely a significant pollution hazard, particularly as it is of low inherent toxicity. The occupational exposure limit to dust is lmgm and the LD50 for oral ingestion is 200mgkg for several species. At these levels, rhodium and its compounds exhibit weak carcinogenicity and adverse reproductive effects have been observed. Nevertheless, rhodium dust and water-soluble rhodium compounds are now found at roadsides as a result of erosion of automobile emission control catalysts. 

Tables 1 and 2 sununarize the development of the legislation in the United States from the time when serious attention was paid to reducing emissions from automobiles. From 1977 in California, where there were some particularly pressing air-quality problems [3], they were allowed to legislate lower levels of emissions than in the rest of the United States. The emission numbers are generated by driving the vehicle on a chassis dynamometer (rolling road) to a well-defined test drive cycle (see Fig. 1). This cycle represents conditions typical on a U.S. freeway and has a maximum speed of 55 mph. The emissions are collected from the tailpipe as soon as the ignition is switched on, analyzed, and the pollutant concentrations calculated. It can be seen from the table that emission limits are decreasing steadily, especially from 1993 onward, and that over the period there has been a major reduction in the emission levels. With the introduction of each successive emissions band, a small percentage of vehicles are required to meet the next band. This culminates in a requirement for a small number of vehicles to emit zero emissions in the year 2000, which can be achieved currently only by electric vehicles.

Initially, fuel sulfur was regulated to reduce emissions of the oxides of sulfur, which contribute to acid rain, ozone, and smog. The recent and stricter round of sulfur specifications, however, are an effort to reduce automobile emissions of the oxides of nitrogen (NO c) and particulate matter (PM). For example, the 15 ppmw diesel sulfur limit follows from the USEPA s parallel program of rule making that seeks to reduce automobile NO and PM emissions by 95% and 90%, respectively, by 2007. Automobile manufacturers are demanding ultra-low-sulfur fuels because only then would their advanced, sulfur-sensitive after-treatment technologies achieve such drastic reductions in NO and PM emissions. 

The other thrust of the air pollution regulations applies to the sources of the pollutants. These regulations are emission standards called the New Source Performance Standards (NSPSs). These sources include stationary sources such as power plants and industrial manufacturing operations as well as mobile somces such as automobiles, trucks, and aircraft. These regulations are mass flow rate-based, that is, grams-poUutant/hr or lb-poUutant/10 Btu. Pollutant-specific emission limits were... 

Workplace exposure limits for benzene have been regulated to levels as low as 0.5 ppm (43). Industrial emissions affecting the pubHc ate now low enough that the EPA considers that a greater hazard exists from mosdy indoor sources such as smoking, automobile exhausts, and consumer products (44). 

We have included in this volume two chapters specifically related to society s kinetic system. We have asked James Wei of the University of Delaware, recent Chairman of the consultant panel on Catalyst Systems for the National Academy of Sciences Committee on Motor Vehicle Emissions, to illustrate key problems and bridges between the catalytic science and the practical objectives of minimizing automobile exhaust emissions. We have also asked for a portrayal of the hard economic facts that constrain and guide what properties in a catalyst are useful to the catalytic practitioner. For this we have turned to Duncan S. Davies, General Manager of Research and Development, and John Dewing, Research Specialist in Heterogeneous Catalysts, both from Imperial Chemical Industries Limited. 

Exposure Levels in Environmental Media. Several studies are available documenting bromomethane concentrations in ambient air (Brodzinsky and Singh 1983 Harsch and Rasmussen 1977), but data for bromomethane in water are rare. Bromomethane has been analyzed for, but rarely detected, in foods (Daft 1987, 1988, 1989). Human exposure levels of bromomethane by inhalation of urban air have been calculated (Singh et al. 1981b). However, these levels are based on monitoring data more than 10 years old. Since urban air concentrations of bromomethane may have decreased due to reduced emissions from automobiles, exposure levels calculated from past data should be taken as an upper limit, and new levels calculated from current monitoring data would be useful. 

Because wholesale bans of this type will not occur, then another approach to achieving safety, at least for pollutants, might be suggested. Why not seek the goal of no detectable chemicals in the media of human exposure If automobiles emit various nitrogen oxides, simply ensure that emission rates are sufficiently low so that these noxious chemicals cannot be found in air. If PCBs are migrating from a hazardous waste site, impose limits on that migration so that no detectable PCBs are found in the off-site environment. Control afla-toxin contamination of raw food commodities to ensure none can be found in finished foods. Why not apply this approach to all pollutants (it obviously is not applicable to products) ... 

Dust (especially from industrial activities) and salt spray will also exacerbate atmospheric corrosion (Section 16.4). In enclosed industrial premises, atmospheric corrosion could be minimized by preventing noxious emissions, filtering the air to remove particulate matter, and scrubbing the air with water to remove SO2 and other objectionable gases, although the humidity should itself be kept as low as possible (e.g., steam leaks should not be tolerated). On the global scale, however, the cost to the public of atmospheric corrosion could be substantially reduced by sharply limiting SO2 and, to a lesser extent, NO. emissions from power plants, smelters, automobiles, and other industrial functions. This is an aspect of the acid rain threat (Chapter 8) that is usually overlooked. 

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