The U.S. Environmental Protection Agency is taking steps to curb the thick black clouds of exhaust from diesel-powered buses that foul the air of Baltimore and the rest of the nation's largest cities.
Prompted by last year's Clean Air Act amendments, the EPA yesterday proposed tightening federal limits on bus pollution. The agency called for an 80 percent reduction in its current diesel particulate emission standard by 1994.
Particulates (soot) are microscopic carbon particles in diesel exhaust that can aggravate asthma, bronchitis and respiratory infections if inhaled. They also are considered a probable human carcinogen.
Buses are a special pollution problem because they vent their exhaust near people in cars and on foot. Emissions also cut visibility.
"We have received more complaints about the huge, black billows of smoke from buses than any other issue relating to vehicles," EPA Administrator William K. Reilly said in a statement accompanying the proposed regulations.
Emission controls would be required on new buses as well as those already on the road. The mandate for cleaner buses follows an earlier EPA order to reduce the sulfur content of diesel fuel to cut particulates.
Starting in 1993, all new buses would have to meet a particulate emission limit of 0.10 gram per brake horsepower-hour, down from the current standard of 0.25. The limit would be even tighter in 1994, no more than 0.05 gram per brake horsepower-hour.
Beginning in 1995, transit officials in Baltimore and 48 other urban areas would have to install new particulate emission "traps" on all buses that are brought in for routine overhauls of their diesel engines.
The cost for Maryland could be significant. The state Mass Transit Administration normally replaces about 80 buses in its 900-vehicle fleet every year, said spokeswoman Helen Dale, but has not bought any new buses since 1990 because of the state budget crunch.
Emission controls will increase the cost of a new bus by about 1 percent, or $2,000, said EPA spokeswoman Kelly Bunker. Retrofitting older buses to meet a 0.10 gram particulate limit could run from $1,500 to $9,000 per vehicle, she said.
But a spokesman for public bus and transit agencies challenged EPA's cost estimates, contending that the particulate "traps" required to meet the new emission limits would add $15,000 to $17,000 to the cost of vehicles that now sell for $175,000.