The California Air Resources Board (CARB) has approved a catalytic particulate filter developed by the Engelhard Corp. to reduce emissions from truck engines operating on a combination of natural gas and diesel fuels. Iselin, NJ-based Engelhard's DPX TM catalytic particulate filter is used right now primarily on dual-fuel engines developed by Clean Air Partners (CAP). Heavy-duty vehicles such as refuse trucks and school buses that operate in urban areas are considered the primary market for these engines, the company said. Engelhard added that its DPX filters are also approved in California under Executive Order D-385-6 for installation on vehicles powered by Caterpillar, Cummins, DDC, International, Mack, and Volvo engines. In addition to reducing particulates, Engelhard said its filter also reduces emissions of aldehydes, non-methane hydrocarbons and carbon monoxide.