Updated 2/14/2011 at 5:30 p.m.

CHICAGO (CBS/WBBM) — An examination of Metra’s pollution problems reveals riders may be at greater risk than originally believed.

As WBBM Newsradio 780’s Mary Frances Bragiel reports, testing was conducted on six dozen Metra trains between November and January.

LISTEN: Newsradio 780’s Mary Frances Bragiel reports

A Chicago Tribune investigation found riders inside the outbound trains, specifically the first car behind the locomotive leaving the south platform at Union Station, were inhaling the highest levels of lung damaging soot.

Metra’s own tests verify what independent published reports indicated.

Standard soot levels on a busy city street measure about 2 micrograms per cubic meter of air. Metra found on one outbound Union Pacific North Run, the car just behind the engine registered 357 micrograms and averaged 30. In the last car, levels peaked at 31 and averaged three.

“There are certain levels of black carbon that are very high on board our trains, inside the passenger cars,” spokeswoman Judy Pardonnet told CBS 2’s Vince Gerasole.

The study also revealed that higher than normal levels were found on outbound trains leaving the LaSalle Street station, which unlike Union Station, is an open-air facility.

Currently, there is no public health standard for on-board air, but Metra is now considering cleaner-burning fuel, exhaust filters and ventilation systems to correct the problem that’s angered some riders.

Questions first mounted about the dangers of soot on Metra trains after an earlier test last year by the Tribune and the Chicago Respiratory Health Association. The test found that Metra trains pulling out of Union Station and the Ogilvie Transportation Center can have air trapped inside passenger cars that contains levels of diesel soot up to 72 times higher than on neighboring streets.

In January, Metra officials announced that preliminary results by independent consultants show that Metra rail cars were not releasing dangerous levels of harmful soot.

Metra officials later tested the air at downtown stations.

Watch & Listen LIVE