by Lorin Hallinan
ou can hardly be on the freeway today without getting stuck at some point behind a diesel exhaust trail. Who hasn't choked on the insidious gunk belched into the air by trucks, buses or a show-off Mercedes Benz?
Diesel pollution is the dirty reality in our air space that Rudolph Diesel never dreamed about when he invented the diesel engine in 1893. To his credit, diesel engines are considered to be one of the world's most efficient, and over the years improvements have been made to their exhaust emissions. But then there's the dark side: Diesel engine exhaust has been pegged as a potential health hazard.

The hit list

By law, the California Environmental Protection Agency (CEPA), Office of Environmental Health Hazard Assessment (OEHHA) in Sacramento has to update regularly the list of chemicals known to the state to cause cancer or reproductive toxicity. The Safe Drinking Water and Toxic Enforcement Act of 1986 (Prop. 65) requires that the governor revise and republish the list of chemicals at least once a year. On Oct. 1, 1990, diesel engine exhaust was added to the list.
In June 1994, the California EPA's Air Resources Board staff put together a lengthy draft report titled "Proposed Identification of Diesel Exhaust as a Toxic Air Contaminant." According to information in the draft, diesel exhaust - an ominous-sounding mixture of gases, vapors and fine particles - is considered a "potential or probable human carcinogen" by several health agencies, including the National Institute for Occupational Safety and Health, and the International Agency for Research on Cancer.
The agencies lump together several components under the "diesel exhaust" umbrella. Some of the exhaust's components, like arsenic, benzene, and nickel, are known to cause cancer in humans. At least 38 other components of diesel exhaust have been listed as toxic air contaminants by the Air Resources Board. Some of those harmful substances include carbon monoxide, oxides of nitrogen, sulfur dioxide, particulate matter, cyanides, metals and ammonia.
Diesel exhaust also came under scrutiny in a June 1994 preliminary report titled "Health Risk Assessment for Diesel Exhaust", compiled by OEHHA and CEPA. The report states "the evidence that diesel exhaust is carcinogenic in rats is clearly sufficient, and in humans the evidence appears to be sufficient. OEHHA staff are considering the conclusion that diesel exhaust is a human carcinogen" and that diesel exhaust is "an air pollutant that may cause or contribute to an increase in mortality or in serious illness, or which may pose a present or potential hazard to human health."

The culprits

Mobile sources are by far the primary sources of diesel exhaust pollution. Heavy-duty trucks, urban buses, passenger cars and light-duty trucks hauling people, products and assorted junk have all contributed to the problem, emitting 41,500 tons of diesel exhaust particulate matter in California in 1990. That's 70 percent of total emissions fouling the air. Other sources, such as ships, trains, farm equipment, and construction equipment, emitted 13,460 tons, or 23 percent the same year.
The good news is that the emission exhaust from mobile sources in California is expected to decrease through 2010 because of emission standards and regulations already adopted by the Air Resources Board and the U.S. EPA. The problem is that by 2010, if no additional standards or regulations are adopted, in light of blossoming population and more cars on the roadways, the emissions are expected to increase, according to the Air Resources Board's draft report.

A backseat concern

Alarm over diesel exhaust pollution has in the past taken a back seat to other more high profile pollutants, such as ozone and smog. Although diesel engine exhaust is considered a potential health hazard, comments from staff at the California Air Resources board seem surprisingly reserved. "Public concern is a little premature," said Jerry Martin, public information officer for the board. "Right now, according to what OEHHA is telling us, and what we measure, it seems that the average Californian is not exposed to a high enough level (of diesel exhaust pollution) to develop cancer from that exposure."
Although OEHHA states in its preliminary report that diesel exhaust is toxic, it's toxic at a level that most Californians are not exposed to, Martin pointed out. "If you were to breathe air which contained five parts diesel soot per one million parts, and if you were to breathe that for 24 hours a day, 70 years straight, you'd have the potential for developing cancer solely from that exposure," said Martin. "That's what OHEEA has said. There are some people, primarily those who work in oil refineries, truckers, around ship ports and loading docks, that may occasionally be exposed to those five ppm levels, but virtually no one we know of is exposed to that level for 70 years nonstop.
"If you were to look at that draft report with that understanding," he added, "you'd say that at current levels in the state, very few people run a risk of developing cancer or birth defects from exposure to toxic soot. But this is a preliminary report. As in any draft report, it's subject to change."
Martin expects an updated report to be issued by the board this fall. He also said that California is already forecasting stricter emissions standards for diesel emissions. Right now, he said, diesel trucks and buses are allowed to emit four grams of nitrogen oxide into the atmosphere per hour of operation. By the year 2,002, that standard will be cut in half.

Least understood pollutant

The Air Resources Board is, however, clearly concerned with what it calls PM10, a measurement of particulate matter 1/l0th to 1/50th the width of a human hair.
Particulate matter is one of the compounds found in diesel exhaust, and it defies simple definition. It's a hodgepodge of windblown dust, scrapings off tires, fuel emitted from manufacturing plants, and other compounds. It's the least understood of the major pollutants, according to Martin, because it consists of so many different compounds, which vary from place to place. In urban settings, there's more of it.
When you breathe in anything containing particulate matter, your lungs suffer. They can't effectively stop or deflect all that pollution, which can deposit itself well into the lung tissue, increasing the potential that you'll get sick or find respiratory illnesses like asthma, emphysema or bronchitis, getting worse.

A better way

According to Roger Pieplow, marketing director for Clean Air Partners Inc., a designer, manufacturer and marketer of conversion systems in San Diego, all engines - gasoline and diesel - can be adapted to run on natural gas or run on a bi-fuel system, with natural gas being half of the fuel source.
If all engines ran on readily available natural gas fuel, the company's literature points out, the United States could reduce fuel cost by $60 billion annually, reduce automotive pollution by 80 percent, eliminate dependence on $50 billion of imported oil every year, and create four million new jobs.
Natural gas burns fuel cleaner than diesel and gasoline, does not emit particulate matter, and is less expensive to process, although it takes more physical space to store than gasoline or diesel fuel. "Take natural gas out of the ground, filter it, dry it, and it's ready to go," said Pieplow. "You have to refine gas and diesel fuel."
Hawthorne Power System in San Diego, which sells tractors and engines, provides natural gas engine conversions at its Kearny Mesa division. According to Scott Smith, product support representative, it costs about $4,000 to $6,000 to convert a gasoline engine, and $7,000 to $9,000 to convert a diesel engine. Obviously, the average consumer isn't likely to spend that kind of money for a conversion, but commercial vehicle owners have an incentive.

Pushing for change

According to the 1992 Energy Policy Act, federal legislation requires certain fleet operators who own 10 or more motor vehicles to use alternative fuels when they purchase new vehicles. The requirements began phasing in last year and will continue to be phased in through 1999, according to Howard Levin, alternative fuels marketing manager at the San Diego Gas & Electric Co.
SDG&E has put into place programs that help demonstrate to local fleet operators the value of natural gas, that it's cheaper and cleaner to use. While only nine consumers in the county drive privately-owned natural gas vehicles, there are over 700 commercial vehicles in San Diego powered by the alternative fuel source, according to Levin, including trucks, transit buses, school buses, vans and even one street sweeper operated by Caltrans.
SDG&E operates 13 public natural gas fueling stations in San Diego County, seven on SDG&E property and six at regular retail gasoline sites, such as Shell, Mobile and Texaco gas stations.
At this point, there aren't enough alternative fueling stations available to make the cost worth a consumer's while. But it's getting easier for commercial vehicles to fill up. Natural gas fueling sources operated by SDG&E are strategically located around the county in Carlsbad, Encinitas, Vista, Escondido, Poway, Rancho Peñasquitos, Kearny Mesa, Miramar, El Cajon, Chula Vista, Otay Mesa, downtown San Diego, and Coronado.
In 1994, the stations dispensed 476,000 therms of natural gas, or the equivalent of 400,000 gallons of gasoline at 75 cents per therm, or the equivalent of 88 cents a regular gallon.
Depending on Utility Commission approval, Levin said SDG&E plans to do a number of things to promote alternative power sources. "We want to develop programs to educate customers about electric vehicles, too," said Levin.
Is it likely that natural gas will replace other fuel sources entirely any time in the near future? "I can't really fathom it totally replacing petroleum products," said Levin. "There are 81/2 billion 42-gallon barrels of petroleum products used for transportation every day in this country."
With the help of federal and state mandates dictating alternative fuel usage, and continuing study conducted by state government agencies, diesel exhaust pollution should pose less of a potential health hazard in the future. But it's too early to breathe easy just yet.

Lorin Hallinan, a regular contributor to Earth Times, is a freelance author and former editor for the Coast Dispatch and Carlsbad Journal community newspapers. A 13-year San Diego resident, she lives in Carlsbad.


If you spot a smoking vehicle on the roadway, you can do something about it. Call the San Diego Air Pollution Control District's toll-free 24-hour smoking vehicle hotline at (800) 28SMOKE. A recorded message will ask for the following information: Your report will help get pollutiong cars and trucks off the roadways.