BOSTON -- The U.S. Environmental Protection Agency announced it's seeking a $33,200 penalty against National Car Rental for excessive bus idling at Logan Airport this past summer.

According to the EPA, National had multiple buses idling for more than five minutes and, in at least one case, for more than an hour. Massachusetts law prohibits engine idling while a vehicle is stopped for more than five minutes. Because the regulation is part of state efforts to meet federal air quality standards, the EPA enforces the regulation.

National Car Rental, a unit of ANC Rental Corp., declined to comment on the EPA's charges and fine.

"Diesel exhaust from buses is a major health concern, especially in our urban neighborhoods," said Robert W. Varney, regional administrator for EPA's New England Office. "These penalties are a sign that we're serious about cutting back on pollution by enforcing rules against excessive idling."

The EPA said inspectors observed the violations at Logan Airport on several days in June and July. Six of National's diesel shuttle buses at Logan Airport were found to be idling for more than five minutes, totaling 332 minutes of excessive idling, the agency said.