"Notwithstanding the difficult economic and political challenges EPA faced, her agency was directly responsible for saving the lives of tens of thousands of Americans and improving the health of millions throughout the country," said S. William Becker of the National Association of Clean Air Agencies. "She will be sorely missed."
Larry Schweiger, head of the National Wildlife Federation, cited her climate change work and efforts to reduce carbon pollution.
Environmental groups had high expectations for the administration headed by Obama, a Democrat, after eight years of President George W. Bush, a Republican and Texas oilman who rebuffed agency scientists and refused act on climate change. Jackson came into office promising a more active EPA.
But she soon learned that changes would not occur as quickly as she had hoped. Jackson watched as a Democratic-led effort to reduce global warming emissions passed the House in 2009 but was then abandoned by the Senate as economic concerns became the priority. The concept behind the bill, referred to as cap-and-trade, would have established a system where power companies bought and sold pollution rights.
"That's a revolutionary message for our country," Jackson said at a Paris conference shortly after taking the job.
Jackson experienced another big setback last year when the administration scrubbed a clean-air regulation aimed at reducing health-threatening smog. Republican lawmakers had been hammering the president over the proposed rule, accusing him of making it harder for companies to create jobs.
She also vowed to better control toxic coal ash after a massive spill in Tennessee, but that regulation has yet to be finalized more than four years after the spill.
Jackson had some victories, too. During her tenure, the administration finalized a new rule doubling fuel efficiency standards for cars and light trucks. The requirements will be phased in over 13 years and eventually require all new vehicles to average 54.5 mpg, up from 28.6 mpg at the end of last year.
She shepherded another rule that forces power plants to control mercury and other toxic pollutants for the first time. Previously, the nation's coal- and oil-fired power plants had been allowed to run without addressing their full environmental and public health costs.
Jackson also helped persuade the administration to table the controversial Keystone XL pipeline, which would have brought carbon-heavy tar sands oil from Canada to refineries in Texas.
House Republicans dedicated much of their time this past election year trying to rein in the EPA. They passed a bill seeking to thwart regulation of the coal industry and quash the stricter fuel efficiency standards. In the end, though, the bill made no headway in the Senate. It served mostly as election-year fodder that appeared to have little impact on the presidential race.
Associated Press writers Lolita C. Baldor and Pauline Jelinek contributed to this report.