Fog Cleans Air Pollution

Reported June 2005

FORT COLLINS, Colo. (Ivanhoe Broadcast News) -- A dreary, foggy morning may wreak havoc on your morning commute. But now, scientists reveal that not all thick, foggy air is bad. Some of it may be helping to clean up our polluted skies.

Commuting to work in the morning is already a long trek for Emilie Lorditch. But add in a blanket of thick, dense fog, and the drive worsens. "It can be really scary," she says.

Atmospheric chemists say poor visibility and traffic tie-ups have given fog a bad rap. Now, new research shows fog is actually good at clearing up something bad -- dust and dirt particles in the air.

"In the case where you have a fog-scavenging air pollution and the fog droplets being deposited to the ground, those pollutants are going with the droplets to the ground," atmospheric chemist Jeffrey Collett, Jr., Ph.D., of Colorado State University in Fort Collins, tells Ivanhoe.

Different kinds of fog appear across the country. But, the kind responsible for air pollution cleanup is called radiation fog. It occurs mostly in the morning.

"Radiation fog forms when the atmosphere is very stable and the skies are clear," Collett says. "And so the ground tends to radiate heat away to the sky."

On a clear night, heat from the ground radiates into space, leaving cool air just above the ground. Once the air reaches a specific temperature, water droplets form, surrounding pollution particles and creating radiation fog. When the sun comes up, it evaporates the water droplets, cleaning the particles out of the air, and leaving dirt and dust on the ground.

Collett says, "The fogs remove a lot of airborne particles, which are problematic for especially people with respiratory health problems." How much pollution the fog can clean out of the air depends on the size of the pollution particles and the size of the water droplets within the fog.

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