Cleaning Up Diesel Engine Pollution

Like many urban residents, I am frequently blasted with diesel fumes from buses and trucks as I navigate city streets. Over the past four years living in Ann Arbor, Michigan and Washington, D.C., I have cleaned black film off the windows of my apartments. This pollution no doubt caused mostly from diesel exhaust. (In fact, the residences were all located immediately adjacent streets frequented by diesel trucks and buses.)

I have long wondered why our country had such regressive laws regarding diesel vehicle exhaust.

Anatomy of Diesel ExhaustThe long-term environmental and medical impact of exposure to diesel exhaust by myself and my neighbors has been well documented. Diesel engines emit a toxic brew of hazardous pollutants. It contains several proven carcinogens, and over 40 substances listed as Toxic Air Contaminants by the state of California. Diesel exhaust also contains high amounts of microscopic particulate matter (PM), which has been linked to asthma, lung cancer, and heart diseases. The illustration to the right shows how the pollutants are fused together in toxic little bundles ready to inhale deep into your lungs.

According to the organization Clean Air Task Force, all the nasty ingredients combined far exceeds EPA standards for acceptable exposure for most Americans. Their major 2005 report on the health impact of diesel exhaust concluded that nationally diesel exhaust posed a cancer risk 7.5 times higher than the combined risk from all other air toxics, and in the U.S. the average lifetime nationwide cancer risk caused by diesel exhaust is 350 times greater than the EPA’s “acceptable” level. (One cancer per million persons over 70) The broader environmental impact of diesel emissions is significant as well. Leaders in the Washington Council of Governments were shocked to discover in 2002 that although diesel vehicles make up only 3% of all traffic, they contribute 30% of the pollutants that cause ground-level ozone.[1]

After decades of crusading by environmental activists, the country is poised to dramatically reduce the huge volume of air pollution emitted by diesel engines. A long-planned EPA regulation that recently took effect has established the fixed path to cleaner air. The regulation is two-fold: it requires refineries to reduce the amount of sulfur in diesel fuel (reducing pollution from all existing vehicles), and requires new diesel engines starting with the 2007 model year meet stringent new standards. First created during the Clinton years, its implementation was delayed by a federal lawsuit by manufacturers which was settled in 2002 when the regulation was upheld by a federal judge. The EPA describes the impact these rules will have this way:

These programs will yield enormous long-term benefits for public health and the environment. By 2030, when the engine fleet has been fully turned over, PM and NOx will be reduced by 250,000 tons/year and 4 million tons/year, respectively. This will result in annual benefits of over $150 billion, at a cost of approximately $7 billion.

The achievement is so significant even the National Resources Defense Council has praised them, saying “When fully implemented, these successes will add up to one of the most significant victories in a generation for public health and the environment … ” However, under the EPA rules millions of polluting diesel engines will remain on the road: the average age for diesel motors is roughly 30 years, with many lasting much longer. Studies have shown the cleaner fuel alone can reduce the amount of particulates by 14-50%, however that still leaves plenty of toxic pollution in the air.

The diesel buses operated by school systems and public transportation agencies will continue to impact particularly vulnerable young and elderly people for decades. A study completed by NRDC, the Coalition for Clean Air, and the University of California found school bus riders are exposed to four times the level of diesel exhaust than passengers in automobiles, and the exhaust levels measured were over 20 times higher than the standard levels constituting a significant cancer risk. The federal government has made grant money available for efforts to retrofit or replace old buses, but no nationwide policy has been adopted.

Many public transportation agencies operate large fleets of aging diesel buses that serve vulnerable passengers like children and the elderly. As of March 2007, our region’s WMATA Metrobus fleet is comprised of 29% compressed natural gas buses, 3% hybrid diesel-electric buses, and a sizable 68% standard diesel models. The agency will add 25 CNG buses in 2007 and 100 hybrid electric buses each year from 2008 to 2012. Although an improvement, with an fleet that currently includes over 900 diesel buses, even these new buses won’t completely replace the diesel fleet. WMATA decided in 2005 to stick with diesel buses instead of moving more aggressively to CNG, a decision roundly criticized by the Washington Post and other critics at the time.[2] The hazard from diesel exhaust is an urban planning issue larger than city buses. If planners seek to urge people to use public transit and live in more compact communities, they must ensure the air in these places is just as clean as the far-flung suburbs.

While it is clear fuel improvements such as biodiesel and low-sulfur fuel will reduce some of the worst pollutants, older high-polluting diesel vehicles will remain in service for years to come. Despite the lingering problems in the U.S., diesel exhaust is a serious problem around the world, where aging vehicles running on dirty fuels create unacceptable levels of air pollution in most world cities. It was in response to this problem that the Partnership For Clean Fuels and Vehicles was organized under the auspices of the United Nations Environment Program in 2002, dedicated to “assist developing countries to reduce vehicular air pollution.”

> Clean Air Task Force Diesel Campaign
> EPA National Clean Diesel Campaign
> UN Partnership for Clean Fuel and Vehicles
> NRDC: The Campaign to Dump Dirty Diesel
> Clean Air Initiative: Cleaner diesel
> Stanford University: “Study refutes notion that diesel-powered vehicles are better for the environment”

[1] Katherine Shaver, “Diesel Trucks, Buses Fueling Pollution Problem, Officials Say,” Washington Post, 19 December 2002, Pg. A13.
[2] “Battle of the Buses,” Editorial, Washington Post, 17 April 2005, pg. B06.

Author: Rob Goodspeed