Just how dirty is a coal-fired power plant? The answer, it turns out, can change a lot from hour to hour.

The pollution that forms downwind of a power plant depends on shifting factors in the air. On some days, the mix produces hardly any of the fine particles that contribute to health problems such as asthma. On others, it can churn out more than twice as much.

What if you could predict when pollution will likely be worse and adjust electricity sources accordingly?

Researchers at the Georgia Institute for Technology say they've developed the first tool that can make those predictions. By pairing data about Georgia's electricity generation with air quality models, they were able to provide "accurate and fast" forecasts that could have saved the state 23 lives and $176 million in health costs between 2004 and 2011. Their results appear in a paper published Monday in the Proceedings of the National Academy of Sciences .

"I was really surprised and interested to see how much difference there is for a given power plant from one day to the next," says co-author Valerie Thomas , a professor of natural systems at Georgia Tech, adding the impact of emissions could change by 100 percent in a single day.

By using the researchers' model, an electric grid operator could know when more pollution was likely to form and then ramp down coal plants, swapping in natural gas or another, cleaner source instead.

The study focused in particular on sulfur dioxide, which can create hazardous particles when it reacts with the atmosphere. Pollution in Georgia was generally worse in summer and during the day: One coal plant's emissions caused more than 40 times the health costs in July versus January in 2007, for example.

To estimate the costs, the scientists used a system created by the U.S. Environmental Protection Agency to quantify the health toll of fine particle pollution, including effects such as emergency room visits and lost work time.

Their plan comes with a big hitch for utilities. Ramping plants up and down to minimize health impacts would have raised electricity generation costs by $83.6 million over the study's eight-year period. While that's less than half of what could have been saved in health costs, it isn't clear how those savings would get factored into utilities' bottom lines.

Southern Company, which via its subsidiary Georgia Power operates the four large coal plants highlighted in the study, said that it has already invested billions in meeting current air standards. "All areas in Southern Company's service territory have air quality that meets the National Ambient Air Quality Standards ( NAAQS ) for particulate matter, which is the focus of this study," the company said through a spokesperson.

The study authors acknowledge that their concept comes with "practical challenges" that would need to be addressed with new policies. But Thomas notes that the adjustments can be done right away, as opposed to waiting for scrubbers to be installed.

"We're not saying, just do this and forget about air pollution control equipment," she says. "This is another means of managing."

In the United States, clean air rules and an influx of cheap natural gas have already contributed to big declines in sulfur dioxide emissions from coal plants in the past two decades. Is this kind of predictive system still relevant?

Yes, according to Thomas, who says the technology could be used in developing countries where pollution controls are not being installed. The Georgia Tech team also wants to apply the model—which could also help forecast the formation of ozone, the subject of new pending U.S. standards —to emissions from cars and trucks.

The study, Thomas says, is just the beginning of a potential new avenue toward pollution cuts: "This is the first time that's it's been shown that it's feasible to do this."

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge .