Duke Energy's coal, natural gas and oil-fired power plants emitted 134.3 million tons of carbon in 2012.
That made Duke, the nation's biggest power company and a prominent Tampa Bay area electricity provider, the country's second-largest emitter of carbon pollution in 2012.
So says the 2014 Benchmarking Air Emissions report released Wednesday by Ceres, Bank of America, several utilities and the Natural Resources Defense Council.
The biggest polluter was Ohio-based American Electric Power, which relies heavily on carbon-heavy coal but ranks only fifth in the nation for power produced. The report tracks power production and emissions of carbon, sodium dioxide, nitrogen oxides and mercury for the 100 largest utilities in the nation.
Overall, carbon pollution is down. Coal accounted for 39 percent of the power produced by the 100 largest companies in 2012, down from 44 percent in 2011.
"The electric power industry is firmly on the path toward a low carbon energy future," said Mindy Lubber, president of Ceres, a nonprofit advocate of sustainable investing. "And history shows that it is not only capable of meeting new pollution limits, but that it can do so while keeping our lights on and our economy growing."
After AEP and Duke, the largest emitters included Atlanta-based Southern Co., Houston-based NRG and the Tennessee Valley Authority.
Tampa's TECO Energy, parent of Tampa Electric, emitted just more than 15 million tons of carbon in 2012, ranking it 35th.