EPA Administrator Lisa P. Jackson said Thursday, Dec. 27, 2012, that she was stepping down from the Cabinet-level post after four years. Jackson, 50, is the first African American to hold the position and a chemical engineer by training. She plans to depart soon after President Obama’s State of the Union address in January.

“I want to thank President Obama for the honor he bestowed on me and the confidence he placed in me four years ago this month when he announced my nomination as Administrator of the Environmental Protection Agency,” said Jackson in a statement.

President Barack Obama has not yet announced a replacement, though he thanked Jackson for her service in a statement. “Under her leadership,” he said, “the EPA has taken sensible and important steps to protect the air we breathe and the water we drink, including implementing the first national standard for harmful mercury pollution, taking important action to combat climate change under the Clean Air Act and playing a key role in establishing historic fuel economy standards that will save the average American family thousands of dollars at the pump, while also slashing carbon pollution.”

Accused by Republicans of running an agency that issued "job-killing regulations," Jackson has faced stiff political opposition in her four years at the EPA. Congressional Republicans and business groups accused Jackson of waging a “war on coal” after she succeed in placing tighter limits on soot.

Jackson doesn’t have another job lined up, but she has been mentioned as a possible candidate for president of Princeton University, where she was an engineering graduate student, the Washington Post reported. Her departion plans cooincide with historical precedence as Cabinet members looking to move on tend to do so at the beginning of a president's second term.

“I will leave the EPA confident the ship is sailing in the right direction, and ready in my own life for new challenges, time with my family and new opportunities to make a difference,” she said.