28 September 2000

The California Air Resources Board (ARB) has approved a comprehensive plan to reduce particulate matter (PM) emissions from diesel fueled engines. The document concludes that diesel PM is associated with a significant cancer risk and recommends an array of control measures, which could be classified in three groups, as follows:

  1. New regulatory standards for all new on-road, off-road, and stationary diesel-fueled engines and vehicles to reduce diesel PM emissions by about 90% overall from current levels;
  2. New retrofit requirements for existing on-road, off-road, and stationary diesel-fueled engines and vehicles where determined to be technically feasible and cost-effective;
  3. New diesel fuel regulations to reduce the sulfur content levels of diesel fuel to no more than 15 ppm to provide the quality of diesel fuel needed by the advanced diesel PM emission controls.

Measures listed under groups 1 and 3 are, for on-road engines, consistent with the proposed federal 2007 emission and fuel sulfur standards. The ARB also calls on the EPA to implement more stringent emission standards for PM from new off-road engines (California is preempted from regulating most categories of new off-road diesel engines).

Measures listed under group 2 are likely to develop into a diesel particulate filter (DPF) retrofit program on unprecedented scale, targeting an overall diesel PM emission reduction of 75% from existing vehicles. This reduction will be achieved through (1) DPF retrofit of both on- and off-road engines, (2) replacement of existing engines with new technology or natural gas engines, and (3) restrictions placed on the operation of existing equipment. These measures would be implemented over the period 2002-2008.

The adopted package also includes new guidelines for permitting stationary diesel engines. These guidelines also call for fitting of certain categories of stationary engines with particulate filters.

While the adopted plan has a non-regulatory character, its approval means ARB staff, over the next several years, will develop up to an estimated 14 regulatory items related to diesel fuel and diesel engines.

The proposal to cut diesel PM emissions results from the ARB’s controversial 1998 decision to identify diesel PM as a toxic air contaminant (TAC), with the potential to cause more than 500 cancer cases per million persons. These cancer risk estimates were based on old railroad worker studies, that have been deemed inappropriate for such conclusions by later independent scientific review.

To aid in implementation of the Plan, ARB has formed a committee of more than 40 international experts to assess the best technology for reducing diesel PM. The Diesel Retrofit Advisory Committee will hold its first meeting in Los Angeles in early November.

The number of diesel engines in California is estimated at over one million on-road and off-road vehicles, about 15,000 stationary engines, and close to 50,000 portable engines.

Source: ARB (Risk Reduction Plan)