Emissions from heavy-duty diesel vehicles are a major contributor
to the total California inventory of particulate matter. Particulate matter is generally classified as PM-10
for particles with diameters of 10 microns or less, or PM-2.5 for particles with diameters of 2.5 microns or
less. Studies show that diesel exhaust primarily consists of PM-2.5.
These emissions post significant environmental and public
health impacts.
Losses in agricultural productivity from total environmental
impacts are estimated by the ARB at $300 million plus per year. Public health impacts associated with
diesel emissions include an increase in various respiratory diseases and cancer. Additionally, excessive smoke
emitted from heavy-duty vehicles continues to be the public's primary air pollution complaint.
In response to these concerns, California Senate Bill (SB)
1997 (Pressley) was enacted in 1988 authorizing the ARB to implement a roadside smoke enforcement program designed
to curtail the excessive smoke emissions resulting from mal-maintained and tampered heavy-duty vehicles. Following
a detailed field study, the ARB implemented the Heavy-Duty Vehicle Inspection Program (HDVIP)
in 1991. Additionally, a companion Periodic Smoke Inspection Program (PSIP)
requiring California fleet owners to self-inspect their fleets for excessive smoke emissions was developed in 1993
in accordance with California SB 2330 (Killea).
The Diesel Risk Reduction Plan
In 1998 the ARB identified particulate matter from diesel-fueled
engines as a toxic air contaminant (TAC). Particulate matter emissions from diesel-fueled vehicles and engines are about 28,000 tons per year in California. These emissions come from a wide variety of sources including over one million on-road and off-road vehicles, about 16,000 stationary engines, and close to 50,000 portable engines. On-road engines account for about 27 percent of the emissions, off-road engines about 66 percent, with the remaining 7 percent from stationary and portable engines. With full implementation of the current vehicle standards on the books and vehicle turnover, diesel particulate matter (diesel PM) will still be about 22,000 tons per year in 2010 and about 19,000 tons per year in 2020.
On a statewide basis, the average potential cancer risk associated with these emissions is over 500 potential cases per million. Diesel PM emissions are estimated to be responsible for about 70 percent of the total ambient air toxics risk. The ARB staff's proposal for dealing with this TAC is the Diesel Risk Reduction Plan which requires all new diesel-fueled vehicles and engines to use state-of-the-art catalyzed diesel particulate filters (DPFs) and very low-sulfur diesel fuel. Further, all existing vehicles and engines should be evaluated, and wherever technically feasible and cost-effective, retrofitted with DPFs. As with new engines, very low-sulfur diesel fuel should be used by retrofitted vehicles and engines. In short, the staff’s proposed plan contains the following three components:
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 percent 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; and
3. New Phase 2 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.
Upon the Board's approval of this comprehensive plan with its various control measures, staff will begin the full regulatory process to develop the actual regulation envisioned by this plan.
The projected emission benefits associated with the full implementation of this plan, including proposed federal measures, are reductions in diesel PM emissions and associated cancer risks of 75 percent by the end of 2010 and 85 percent by the end of 2020. The measures recommended in this plan will have a great impact on reducing the localized risks associated with activities that expose nearby individuals to diesel PM emissions. Further, there are other benefits associated with reducing diesel PM emissions. These include reduced ambient fine particulate matter levels, increased visibility, less material damage due to soiling of surfaces, and reduced incidences of non cancer health effects, such as bronchitis and asthma. Staff expects that the costs associated with carrying out this plan will be significant and will be on the order of the costs associated with other major ARB programs.
