The tailpipe emissions are captured in plastic bags for later analysis.
One possible alternative to the pressure test would involve tightening restrictions on tailpipe emissions.
For those vehicles that run on electricity, the tailpipe emissions are zero.
President Clinton gave final approval last week to strict new federal regulations on tailpipe emissions that will also take effect with the 2004 model year.
That program also calls for some improvements in tailpipe emissions over the years.
California, for example, requires that 2 percent of all new cars sold in 1998 have no tailpipe emissions.
"We believe now it is probably in the rainfall" as a result of tailpipe emissions.
He was also skeptical of moves to further reduce tailpipe emissions.
California mandates that 2 percent of all vehicles sold by each company there in 1998 must have zero tailpipe emissions.
One of the Agency's key aims is to reduce tailpipe emissions.