The following editorial appeared Monday in the Washington Post:

Every time you start up your car, it spews a smelly mixture of gases that wafts into the atmosphere, reacts in the sunlight and forms the brownish haze called smog. Along with those gases come soot and other substances that condense into fine particles. The result, the Environmental Protection Agency reckons, is more than 158 million Americans inhaling unhealthy air.

That's why the EPA announced Friday that it will require big cuts in a range of tailpipe emissions, to be phased in between 2017 and 2025. Oil refiners will have to remove more sulfur from the gasoline they produce, and the EPA expects carmakers to install improved technology to limit pollution.

These rules match those already in place in California, Europe, Japan and South Korea. The EPA estimates that, phased in nationally, they will prevent up to 2,400 premature deaths, 3,200 hospital visits, 22,000 asthma attacks and 1.8 million lost school and work days every year.

Auto manufacturers like the rule because it will harmonize policy across all 50 states. But refinery companies point to a study from last year that concluded the EPA's rule would raise gas prices by as much as 9 cents a gallon. Yet that study didn't assess the rule the EPA ended up proposing. The actual rule gives refineries flexibility, allowing them to average the sulfur content across the pool of gasoline they produce and to make capital improvements over many years. It is particularly lenient with small refineries, offering them a longer phase-in period. The agency estimates the cost at about a cent a gallon.

Even that would be too much if the public health benefits were negligible. The EPA's figures indicate that costs in 2017 might rival the value of the benefits, if those benefits come in at the very low end of the agency's estimates. But the cost-benefit picture improves quickly: By 2030, the EPA calculates, the benefits of the program will outweigh costs by at least 2 to 1 - and possibly by as much as 7 to 1.

President Obama's first term saw some landmark new environmental standards. His second should be even more controversial.

In cases such as this one, in which the cost-benefit picture is favorable, the president should no longer hesitate.