Emissions Performance

Reductions in vehicular emissions are a key goal of programs to develop advanced technology vehicles. In California, it is the only explicit goal, although other considerations, such as economic development, are important. Furthermore, PNGV’s original name was the Clean Car Initiative.

The drive to ratchet down the emissions of new vehicles is highly controversial. One reason is that most vehicular emissions come from older vehicles, or relatively new vehicles whose emission controls are malfunctioning. Automakers have long argued that new control requirements that raise the price of new vehicles have the effect of slowing new vehicle sales and, thus, reducing fleet turnover-the primary source of improved fleet emissions (and fuel economy) performance. Further, there is substantial disagreement about how much new controls will cost, and thus similar disagreement about their balance of costs and benefits.

Each of the advanced vehicles examined by OTA have emission characteristics that are different from current vehicles as well as from the baseline (business-as-usual) vehicles expected to enter the fleet, if there are no new incentives for significant changes in vehicle technology. A number of changes that will yield improvements to new vehicles’ emission performance, however, already are programmed into vehicle development programs. Both the federal Clean Air Act and California’s Low Emission Vehicle Program require significant improvements in the certified emission levels allowable for new light-duty vehicles, as well as an extension of the certified “lifetime” of required control levels from 50 thousand to 100 thousand miles. New requirements for onboard diagnostics to alert drivers and mechanics to problems with control systems, more stringent and comprehensive inspection and maintenance testing (including testing for evaporative emissions), and expansion of certification testing procedures to include driving conditions that today cause high emission levels should ensure that actual on-road emissions of average vehicles more closely match the new vehicle certification emissions levels.

The Advanced Conventional vehicles will most closely resemble the baseline vehicles’ emissions performance. By 2015, however, these vehicles will have direct injection engines-either diesel or gasoline. These engines should have lower cold start and acceleration enrichment-related emissions than conventional gasoline engines. This should have a positive impact on emissions, although new regulations should force down such emissions even in the baseline case. A key uncertainty about emissions performance for these vehicles is the performance of the NOX catalysts, which currently remain under development. Another area of concern, for the diesels, is particulate emissions performance; although new diesel designs have substantially reduced particulate emissions, these emissions levels are still considerably higher than those of gasoline vehicles.

The key emissions advantage of EVs is that they have virtually no vehicular emissions regardless of vehicle condition or age-they will never create the problems of older or malfunctioning “super-emitters,” now a significant concern of the current fleet. Because EVs are recharged with powerplant-generated electricity, however, EV emissions performance should be viewed from the standpoint of the entire fuel cycle, not just the vehicle. From this standpoint, EVs have a strong advantage over conventional vehicles in emissions of HC and CO, because power generation produces little of these pollutants. Where power generation is largely coal-based—as it is in most areas of the country-some net increases in sulphur dioxide might occur. However, Clean Air Act rules “cap” national powerplant emissions of sulphur oxides (SOX) at about 9 million tons per year, which limits the potential adverse effects of any large-scale increase in power generation associated with EVs Any net advantage (or disadvantage) in NOX and particulate emissions of EVs over conventional vehicles is ambiguous, however. All fossil and biomass-fuelled power generation facilities are significant emitters of NOX , and most are significant emitters of particulate, although there are wide variations depending on fuel generation technology, and emission controls. Analyses of the impact of EVs on NOX and particulate emissions are extremely sensitive to different assumptions about which powerplants will be used to recharge the vehicles, as well as assumptions about the energy efficiency of the EVs and competing gasoline vehicles 63 and the likely on-road emissions of the gasoline vehicles. OTA estimates that the year 2005 lead acid EVs will most likely increase net NOX on a nationwide basis, with the NiMH batterypowered vehicle about breaking even, but that the combined effect of increased NOX controls on powerplants, a continuing shift to cleaner generating sources, and increases in EV efficiency will allow the more efficient EVs in 2015 to gain a small net reduction in NOX emissions.

Hybrid vehicles have been generally considered as likely to have significantly lower emissions than conventional vehicles because of their smaller engines and the supposition that these engines would be run at constant speed and load (for series hybrids). There have been various reports of hybrids attaining very low emissions—below ultralow emissions vehicle standards-in certification-type testing.

One key advantage for some hybrids will be their ability to run in an EV-mode in cities, although their performance or range may be limited in this mode. Other advantages are less certain, however. Hybrids will likely not run at constant speed, although their speed and load excursions will be less than with a conventional vehicle; they must cope with cold start and evaporative emissions essentially similar to a conventional vehicle; and their engines may be stopped and restarted several times during longer trips, raising concerns about increased emissions from hot restarts. In OTA’s view, hybrid vehicles with substantial EV range have clear emission advantages in this mode, but advantages in normal driving are unclear.

Fuel cell vehicles will have zero emissions unless they use an onboard reformer to process methanol or another fuel into hydrogen. Emissions from the reformer should be extremely low in normal steady-state operation, but there may be some concern about emissions during increased loads, or the potential for malfunctions. In particular, the noble metal catalyst needed for the reformer can be poisoned in the same manner as the catalyst on a gasoline vehicle.