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Colorado has traditionally been known as a pristine state with clean air, but ground-level ozone and smog are changing that. Not every county in Colorado…

In eastern Kansas, ranchers burn the prairie every spring to bring back grass for grazing cattle. Environmentalists celebrate those fires because without them the delicate ecosystem would disappear.

The case focuses on the Clean Air Act permitting required of companies that want to build or modify facilities expected to emit a lot of gases. Critics call the requirement costly and time-consuming.

Colorado’s Air Quality Control Commission is considering rules that would set limits for emissions and require more extensive efforts to monitor and fix…

Calling them ‘groundbreaking,’ Governor John Hickenlooper proposed new statewide air quality rules for oil and gas drilling Monday. The rules aim to…

The Chinese city is trying something new to placate tourists disappointed by the curtain of smog that now envelops the classic skyline.

The haze, caused by clear-cutting fires in neighboring Indonesia, has enveloped much of the country's south as well as the city-state of Singapore.

The choking haze that's enveloped the city state is being caused by brush fires in Indonesia, and Singapore's premier says it could last for weeks.

The move would not require congressional approval, but it is sure to be controversial. Electric power plants are said to be responsible for nearly 40 percent of greenhouse emissions.

Scientists are trying to figure out how chemicals in the air interact with each other to make people sick. So they're building an instrument — a "lung in a box" — that goes way beyond the usual chemical monitors.