Hien T. Tran, the California Air Resources Board scientist who was the lead author and project coordinator of the study justifying the air board's sweeping new efforts to limit diesel emissions, is being investigated by air board officials over allegations he lied about having a Ph.D. in statistics from the University of California at Davis. "We're going to take the appropriate actions if this is true," Leo Kay, ARB's director of communications, told me. James E. Enstrom, an epidemiologist with the UCLA Jonsson Comprehensive Cancer Center, raised the questions about Tran's qualifications in a Dec. 10 letter to the air...