After years of delay, the Obama Administration faced a court-ordered December 1 deadline to update the current 2008 standard on ground-level ozone, a by-product of burning fossil fuels. Its proposal to toughen the ozone limit is one of several sweeping environmental efforts that have drawn opposition from Republicans in Congress and business groups because of potential economic costs.

"Bringing ozone pollution standards in line with the latest science will clean up our air, improve access to crucial air quality information, and protect those most at risk," Environmental Protection Agency Administrator Gina McCarthy said in announcing the standard. The EPA said that the people most affected by smog are children, older adults, and those who suffer from asthma or spend a