Vehicle Emissions Reduction

Jump to related links Jump to related documents

Gasoline

Lead additives Sulfur

Other gasoline modifications Conclusions

The pollutants of greatest concern from gasoline-fueled vehicles are carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), lead (Pb), and certain toxic hydrocarbons such as benzene. Each can be influenced by the composition of the gasoline used.

The most critical issue in most developing countries is whether or not to reduce or eliminate the use of lead based additives.

In addition -- as catalytic converter technology is used as the primary means of reducing tailpipe emissions of CO, HC, and NOx -- sulfur levels are seen as increasingly important because performance of advanced catalyst-based systems is impaired by sulfur or, in some cases, precluded by it.

Lead does not exist naturally in gasoline; it must be added to it.

Because lead is a relatively inexpensive way to boost gasoline octane and enhance performance, a few years ago almost all gasoline used worldwide contained lead and, in many cases, at concentrations above 0.4 grams per liter.

Since the early 1970's, however, there has been a steady movement toward reduced lead in leaded gasoline and increasingly, the complete elimination of lead. Approximately 80% of all gasoline sold throughout the world is now unleaded.

Fifty eight (58) countries are estimated to either already have phased out the use of leaded gasoline or are expected to do so before the end of 2001:

Virtually all modern gasoline fueled vehicles being produced today can operate satisfactorily on unleaded fuel and approximately 90% of these are equipped with a catalytic converter, which requires the exclusive use of lead-free fuel.

There is no longer any doubt that lead is toxic and prevents the use of clean gasoline vehicle technology which can dramatically reduce CO, HC and NOx emissions.

Eliminating lead in gasoline has been demonstrated to dramatically lower ambient lead levels. For example,

Other issues related to lead additives:

• Reduced vehicle maintenance costs with unleaded fuel
• Potential for catalysts to reduce emissions
• Is valve seat recession a problem without lead?

For cars without a catalytic converter, the impact of sulfur on emissions is minimal; however for catalyst-equipped cars, the impact on CO, HC and NOx emissions can be substantial. As noted by the US Auto-Oil study, "The regression analysis showed that the sulfur effect (lowered emissions) was significant for HC on all ten cars, for CO on five cars, and for NOx on 8 cars. There were no instances of a statistically significant increase in emissions." Based on the auto/oil study, it appears that NOx would go down about 3% per 100-PPM sulfur reduction for a typical catalyst equipped car.

The situation is even more critical for advanced low pollution catalyst vehicles. Operation on typical US conventional gasoline containing 330-ppm sulfur will increase exhaust VOC and NOx emissions from current and future new US vehicles (on average) by 40 percent and 150 percent, respectively, relative to their emissions with fuel containing roughly 30-ppm sulfur.

In light of these impacts, it is not surprising that Japan has had typical gasoline sulfur levels under 30 PPM for many years. The US has also adopted a 30-PPM sulfur limit. As the European Union tightened its emissions limits in 2000 (so called Euro 3 standards), it required a lowering of the sulfur content in gasoline to 150 PPM; for the Euro 4 standards in 2005, it will require gasoline with a maximum sulfur content of no more than 50 PPM. Even more recently, the European Union has proposed to limit sulfur levels to a maximum of 10 PPM.

Beyond the elimination of lead and the reduction of sulfur, it is possible to make additional modifications to gasoline, to "reformulate" it to reduce both regulated and unregulated emissions of concern. As part of a comprehensive policy to reduce vehicle emissions, fuel reformulation has the potential not only to offset any increased risks associated with the introduction of unleaded petrol but to complement the elimination of lead health risks with an overall reduction of the toxic and ozone forming potential of gasoline and gasoline vehicle emissions.

The potential for "reformulating" gasoline to reduce pollutant emissions attracted considerable attention in the US as pressure to shift to alternative fuels increased during the mid to late 1980's. One result was a major cooperative research program between the oil and auto industries. During the early 1990's, this was followed by a similar effort in Europe. The result is that a great deal has been learned about the potential for modifying gasolines in a manner that can significantly improve air quality. An additional advantage of fuel reformulation is that it can reduce emissions from all vehicles on the road in much the same way that reducing lead in gasoline can reduce lead emissions from all vehicles.

• Lowering volatility
• Benzene
• Oxygenates
• Reducing olefins, aromatics and T90

• A growing body of data on the adverse health effects of lead, especially in young children, indicates there may be no "safe" level. Reduced lead in gasoline has been shown to reduce the risk of behavioral problems, lowered IQs and decreased ability to concentrate in exposed children.
• Lead scavengers, which accompany leaded gasoline, have also been identified as human carcinogens; the elimination of lead in gasoline will therefore also reduce this cancer risk.
• Studies in both Europe and the United States show that gasoline lead is responsible for about 90 percent of airborne lead and that 1 microgram per cubic meter of ambient lead will cause a 1-2 microgram per milliliter increase in blood lead levels. This is in addition to the lead burden, which may be associated with food, drinking water and other sources; this burden can be highly variable from country to country.
• The availability of lead free gasoline can facilitate extensive reductions in the other major pollutants from motor vehicles, hydrocarbons, carbon monoxide and nitrogen oxides by allowing the use of catalytic converters.
• Motor vehicle emissions of hydrocarbons, carbon monoxide and nitrogen oxides cause or contribute to a wide range of adverse impacts on public health and general well being including increased angina attacks in individuals suffering from angina pectoris, greater susceptibility to respiratory infection, more respiratory problems in school children, increased airway resistance in asthmatics, eye irritation, impaired crop growth, dead lakes and forest destruction.
• The combination of lead free gasoline and catalysts can also facilitate very substantial reductions in other harmful pollutants such as aldehydes and polynuclear aromatic hydrocarbons (PAHs).
• These emissions reductions can occur simultaneously with equally significant improvements in fuel economy and reductions in vehicle maintenance. Also, based on studies in Canada, reduced maintenance can save about 2.4 cents per liter with the use of unleaded gasoline compared to leaded gasoline.
• The most direct strategy for eliminating lead in gasoline is to ban its use and many countries around the world have already done so.
• Tax policies which price unleaded fuel substantially below leaded fuel have also been found to be very effective in stimulating the sales of unleaded fuel. Hong Kong and Singapore stand out as Asian examples.
• Beyond unleaded gasoline, hydrocarbons, CO and toxic emissions can be reduced from 10 to 30% through the reformulation of gasoline by modifying parameters such as volatility, oxygenates, sulfur levels and hydrocarbon mix. Care must be taken to assure that these modifications don't increase NOx emissions.
• The use of oxygenates such as MTBE (methyl tertiary-butyl ether), while clearly bringing about significant reductions of CO, has raised concerns regarding adverse impacts on drinking water.

• Center for Energy and Environmental Studies - Research on Leaded Gasoline Phase-Out
  [Princeton University]
• Platts
• Blue Ribbon Panel for Reviewing Use of MTBE

• Phasing Out of Lead Gasoline: An Examination of Policy Approaches in Different Countries
  UNEP, 1999 [PDF]