HIGHLIGHTS

• Diesel exhaust is a mixture containing over 450 different components, including vapors and fine particles coated with organic substances.¹⁰ Over 40 chemicals in diesel exhaust are considered toxic air contaminants by the State of California (see Table 1). Exposure to this mixture may result in cancer, respiratory effects, and other health problems.
  
  
• California's Scientific Review Panel has unanimously endorsed the official listing of diesel exhaust as a toxic air contaminant, due to its cancer and non-cancer health effects.
  
  
• Diesel exhaust has been listed as a known carcinogen under California's Safe Drinking Water and Toxic Enforcement Act (Prop. 65) since 1990.² Many components of diesel exhaust, such as benzene, arsenic, dioxins, and formaldehyde, are also known carcinogens in California. Other components, such as toluene and dioxins, are known reproductive toxicants.
  
  
• For the same load and engine conditions, diesel engines spew out 100 times more sooty particles than gasoline engines.¹⁰ As a result, diesel engines account for an estimated 26 percent of the total hazardous particulate pollution (PM10) from fuel combustion sources in our air, and 66 percent of the particulate pollution from on-road sources.¹¹
  
  
• Diesel engines also produce nearly 20 percent of the total nitrogen oxides (NOx) in outdoor air and 26 percent of the total NOx from on-road sources.¹² Nitrogen oxides are a major contributor to ozone production and smog.
  
  
• The health risk from diesel exposure is greater for children, the elderly, people who have respiratory problems or who smoke, people who regularly strenuously exercise in diesel-polluted areas, and people who work or live near diesel exhaust sources.
  
  
• According to an expert estimate, lifetime exposure to diesel exhaust at the outdoor average concentration (2.2 micrograms per cubic meter (µg/m³) may result in about one in every 2,000 people developing cancer due to this exposure. This estimate increases to as many as one in every 1,200 at levels found in the South Coast Air Basin in Southern California (3.6 µg/m³), and to even higher risks for those living near freeways or in highly polluted urban communities.¹³
  
  
• Dozens of studies link airborne fine particle concentrations to increased hospital admissions for respiratory diseases, chronic obstructive lung disease, pneumonia, heart disease and death.¹⁴ Recent evidence indicates that diesel exhaust exposure may contribute to asthma.¹⁵
  
  
• About 127 million Americans -- half of the nation's population -- live in regions with air quality that does not meet federal standards for certain air pollutants.¹⁶ More than 60 percent of preadolescent children, including children with asthma, live in "nonattainment" areas. In the United States, there are an estimated 10.3 million people living with asthma.¹⁷
  
  
• In California, there are six million children under the age of fourteen, 90 percent of whom live in areas that fail to meet state and federal air quality standards.¹⁸ According to the American Lung Association, there are over a half million children with asthma in California.
  
  
• Asthma is on the rise.  In the United States, age-specific death rates from the disease increased 118 percent between 1980 and 1993.¹⁹   African-American and Latino children have a higher risk of asthma than white children.²⁰ Moreover, African-American children are four times more likely to die from asthma compared to Caucasian children.¹⁹
  
  
• Cleaner alternatives to diesel engines are readily available. Alternatives include electric, liquefied natural gas (LNG) or compressed natural gas (CNG) buses and trucks.
  
  
• Although initial purchase prices may be higher for alternative fuel buses and trucks, federal, state, and local funds are available to offset these higher costs. These funds are specifically earmarked for clean technologies and would not otherwise be available for these purchases.
  
  
• For transit authorities, use of alternative fuel buses can generate operational cost savings. Sacramento RTD's CNG bus fleet is currently demonstrating cost savings of 20-40% per mile when compared to diesel counterparts. Over its lifetime, a CNG bus will save 190,000 gallons of diesel fuel compared to a new diesel bus, decreasing our dependency on petroleum.²¹
  
  
• Diesel buses and trucks are important contributors to smog (ground-level ozone) and fine toxic soot, two pollutants that have recently come under increased scrutiny because of their important public health impacts. Purchasing alternative fuel vehicles will reduce smog and fine soot emissions considerably. For example, operating a natural gas bus instead of a new diesel bus is equivalent to eliminating the smog and soot from 17-55 passenger cars.
  

Notes

2. Cal EPA, Chemicals Known to the State to Cause Cancer or Reproductive Toxicity, Revised May 1, 1997.

10. Mauderly JL. Diesel Exhaust in Lippman M. (ed.) Environmental Toxicants: human exposures and their health effects. Van Nostrand Reinhold, New York, 1992.

11. ARB, Draft Diesel Exposure Assessment, February 1998, p. A-24; American Automobile Manufacturers Association. 1997. Motor Vehicles Facts & Figures 1997. Detroit, Michigan. p. 78.

12. American Automobile Manufacturers Association. 1997. Motor Vehicles Facts & Figures 1997. Detroit, Michigan. p. 40.

13. Calculations based on Hattis D, A Probability-Tree Interpretation of the California EPA's Analysis of the Cancer Risk from Diesel Particulates. Submitted to the ARB on March 19, 1998. Unit risk point estimate is 230 per million at 1 µg/m³. The risk of cancer is about 500 per million at 2.2 µg/m³, and 830 per million at 3.6 µg/m³.

14. U.S. EPA, Office of Air Quality Planning and Standards, "Review of the National Ambient Air Quality Standards for Particulate Matter: Policy Assessment of Scientific and Technical Information," April 1996, ch. 12, Figure 12-1, p. 101; Table 12-15, pp. 151-152, and discussion at pp. 84 - 103, and Table 12-2, pp. 34-46.

15. Wade, JF and LS Newman, Diesel asthma. Reactive airways disease following overexposure to locomotive exhaust, J Occup Med, 35(2):149-54, Feb 1993; Peterson, B and A Saxon, Global increases in allergic respiratory disease: the possible role of diesel exhaust particles, Ann Allergy Asthma Immunol 77(4):263-8; 269-70, Oct 1996.

16. EPA, National Air Quality and Emissions Trend Report, 1995, 1996.

17. Morbidity and Mortality Weekly Report, 41(39), Oct 2, 1992, p. 733-735.

18. Kun, V., et al., Out of Breath: Children's Health and Air Pollution in Southern California, NRDC, Los Angeles, October 1993.

19. Morbidity and Mortality Weekly Report 45(17), May 3, 1996, pp. 350-51.

20. Weitzman M et al., Racial, Social and Environmental Risks for Childhood Asthma, AJDC, 144: 1189-94, November 1990; Schwartz J et al., Predictions of Asthma and Persistent Wheeze in a National Sample of Children in the United States, Am. Rev. Respir. Dis., 142:555-562, 1990; Cunningham J et al., Race, Asthma and Persistent Wheeze in Philadelphia School Children, Am. J. of Pub. Health, 86:1406-1409, October 1996.

21. Campbell, T.R., and Mark J. Critical Assessment of Muni's Alternative Fuel Feasibility Report. Natural Resources Defense Council, Union of Concerned Scientists. December 30, 1997. p. 19. Gross, Marilyn, and Richard N. Feldman. National Transportation Statistics 1997. Bureau of Transportation Statistics: US Department of Transportation. December, 1996.