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San Joaquin County Community Diesel Engine Emission Control Technologies _ Development Department Generally speaking,catalysis can potentially generate other harmful chemical species besides sulfates and NO2. It was found in a Southwest Research Institute study, for instance,that a DOC significantly increased the nitro-polyaromatic _ hydrocarbons(nPAH)in diesel exhaust(Pan 2000). A study by the New York State Department of Environmental Conservation indicates,however, that passive catalyzed diesel particulate filter(DPFs)can effectively reduce nPAH emissions(Lanni 2001). The procedure recognizes the general problem of secondary emissions by allowing for California Air Resources Board(ARB)to request additional exhaust analysis beyond criteria pollutant and PM emission measurements, should there be reason for concern Diesel Particulate Filters In general, a DPF consists of a porous substrate that permits gases in the exhaust _ to pass through but traps the PM. DPFs are very efficient in reducing PM emissions; they can typically achieve PM reductions in excess of 90 percent. Most DPFs employ some means to periodically regenerate the filter(i.e.,burn off the accumulated PM). These can be divided into two types of systems,passive and active. Passive Diesel Particulate Filters A passive DPF is one in which a catalytic material,typically a platinum group metal,is applied to the substrate. The catalyst lowers the temperature at which trapped PM will oxidize to temperatures periodically reached in diesel exhaust. _ No additional source of energy is required for regeneration,hence the term "passive." Field experience has indicated that the success or failure of a passive DPF is primarily determined by the average exhaust temperature at the filter's inlet and the rate of PM generated by the engine. These two quantities,however, are determined by a host of factors pertaining to both the details of the application and the state and type of engine being employed. As a result,the technical information that is readily accessible can sometimes serve as a guide, but may be insufficient to determine whether a passive DPF will be successful in a given application. The PM emission level that an engine was initially certified to, for instance, is based on PM generated and measured over a single prescribed test cycle. Testing done by West Virginia University,however, shows that a given diesel truck can generate a wide range of PM emission levels depending on the test cycle chosen _ (Nine, et al 2000). How well an engine has been maintained is another factor in determining the actual PM emission rate. The ARB's informational package for its heavy-duty vehicle inspection programs lists sixteen different common causes of high smoke levels that are related to engine maintenance(Air Resources Board 1999). DeSilva Gates Quarry Project Draft Environmental Impact Report L-2 J&s mlo& 5