Center for Environmental Research and Technology

The reduction of emissions and fuel consumption using fuels that are renewable and have lower emission rates can provide considerable benefits for national parks such as Yosemite. One fuel that has shown considerable promise in meeting these needs is biodiesel. To date, a number of studies have demonstrated emissions reductions for biodiesel fuels relative to ordinary diesel fuel (U.S. Environmental Protection Agency, 2002). Biodiesel is commercially available and also more readily implemented than other alternative fuels, such as natural gas. Biodiesel requires no modifications to the engine and only minor modifications to existing fuel practices. An added benefit of biodiesel fuels is that they can be derived from renewable, domestic resources, such as crops or waste grease. As such, biodiesel has been designated as an alternative fuel under the Energy Policy Act (EPACT). This allows fleet operators to meet the EPACT alternative fuel vehicle (AFV) acquisition requirements. Biodiesel is added to conventional diesel at blends of 20 percent and higher. The use of biodiesel in fleet and other applications has expanded considerably in recent years, from essentially negligible levels in 1998 to 20 million gallons in 2002 (McCormick, 2003). This includes municipal fleets, military applications, postal applications, and others. The production capacity in the U.S. could be 150 million gallons per year. In Europe, production is currently at 200 million gallons, with a capacity of 600 million gallons. As the use of biodiesel continues to expand, fleets are continuing to examine potential applications of biodiesel. Yellowstone National Park has conducted a demonstration program (University of Idaho and Montana Department of Environmental Quality, 1999). Channel Island National Park is also using biodiesel on a regular basis. Currently, DNC Parks and Resorts at Yosemite, Inc. (DNC) is considering the use of biodiesel in its fleet vehicles for applications in the park. DNC generates approximately 48 tons of used restaurant grease per year that is currently being transported back to Fresno where it is used to make biodiesel. However, the biodiesel is not returned to Yosemite for use in their fleet. The DNC goal is to make use of its restaurant grease and at the same time provide a renewable fuel for use in its fleet vehicles. Prior to full-scale application of the biodiesel, DNC proposed a pilot program to examine the use of biodiesel in their fleet in terms of emissions benefits, maintenance, use during cold weather, and other considerations. If the application of the fuel proves to be successful, eventually the program could lead to development of a small-scale plant on the park grounds that could process the restaurant grease into biodiesel on-site. The present project is a pilot demonstration program in the DNC fleet vehicles. The overall program included an investigation of feasibility of a biodiesel plant, emissions testing, and characterization of fuel mileage and maintenance issues with biodiesel use. The program is a collaborative effort between DNC, the California Integrated Waste Management Board, the University of California at Riverside, the Air Resources Board, Clean Air Technologies, Inc., and Biodiesel Industries.

This paper presents an analysis of data from a wind tunnel study conducted to examine the dispersion of emissions at the edges of near-road noise barriers. The study is motivated by the concern that a barrier positioned downwind of a roadway may guide highly polluted plumes along the barrier leading to heightened concentrations as the plume spills around and downwind of the barrier end. The wind tunnel database consists of measurements of dispersion around a simulated roadway segment with various noise barrier configurations. Each roadway segment simulated in the wind tunnel had full-scale equivalent dimensions of 135 m long. Barrier segments, 135 m long with a height (H) of 6 m, were located on the downwind side of the source at a distance of 18 m from it (measured perpendicularly from the line source). Examination of the concentration patterns associated with the cases indicates that 1) vertical mixing induced by barriers persists at crosswind distances up to the edge (lateral end) of the barrier and downwind distances of x/H = 10, 2) concentration levels at all heights below z/H = 1 increase towards the edge of the barrier at downwind distances less than x/H = 7, and 3) concentration is well mixed in the vertical at the edge of the barrier, and the levels can be higher than in the middle of the barrier even when the source ends at the edge of the barrier. We have formulated a parameterization that captures the major features of these observations and can be incorporated in models such as RLINE.