Special filters intended to decrease emissions by diesel trucks of particulate matter 2.5 are required by the California Air Resources Board to be equipped on all diesel trucks that operate in California. If the filters are judged to be successful in decreasing air pollution, some observers worry that the U.S. Environmental Protection Agency will encourage more states to mandate their use.

Such encouragement from EPA would come despite litigation charging that the filters endanger drivers and others with extremely high-temperature fires, significant economic losses, and doubts about the device’s effectiveness in reducing harmful emssions.

The crucial research that formed the basis for the regulation mandating use of the filters was led by Hien Tran, who faked his Ph.D. credentials, a fact initially kept from board members by CARB Chairman Mary Nichols. Nichols is a former senior federal environmental executive.