The move is usually reserved for severe human rights violations.
New Delhi has the worst air quality in the world.
Reports of a cloud of darkness blocking out the Sun at noon above northern Siberia have raised questions.
Air in China on Wednesday was nearly too dangerous to breath.
Between 25 and 41 percent of nitrogen oxide is emanating from agricultural lands in California.
The number of days when smog posed a high health risk have doubled in the last year.
Killer smog in China has paralyzed some of its top cities in the past—so much so that its defense now includes the world's biggest air purifier.
Temperatures in the Golden State could reach as high as 122 degrees.
Experts couldn't measure just how bad the air pollution was because the sandstorm caused traditional measuring instruments to break.
Over 126 million Americans—about 40 percent—live in areas that fail to meet environmental standards.
The report also suggests building huge ventilation tunnels to create wind which will lift the smog from the city
Poor air quality has plagued the country's north, triggering a red alert in Beijing.
Another tightening of EPA standards this year could trip up automakers.
The announcement marks the first red alert in the city's history.
There are just a few minutes on the clock, says Ed Begley Jr., but the game is definitely not over
The agency's scientists warned against setting the limit at this level.
Ozone is linked to asthma, heart disease, premature death, and an array of pregnancy complications