June 1, 2005 While it hassles commuters, morning mist removes a lot of airborne particles which are hazardous for people with respiratory health problems. The water droplets inside morning fog are of just the right size to collect and hold onto tiny air pollutant particles floating in the air. Once the fog settles back to the ground, it takes the air pollution particles with it.
FORT COLLINS, Colo.--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., of Colorado State University in Fort Collins, tells DBIS.
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.
BACKGROUND: Jeffrey Collett, an atmospheric scientist, has discovered that radiation fog in valleys -- such as California's San Joaquin Valley -- can help "clean" the air of pollutants.
WHAT IT IS: Radiation fog is common in the mornings. After sunset, the ground cools, radiating heat away. If there are in calm conditions with a clear sky, the cool ground then produces condensation in the nearby air. It is also known as "ground fog" and "valley fog."
ABOUT AIR POLLUTION: Air pollution is made up of many kinds of gases, droplets and particles that can remain suspended in the air. This makes the air dirty. The easiest way to visualize airborne particles (also called aerosols) is to exhale outside on a cold day and watch the fog come out of your mouth when water vapor forms water droplets. The same thing happens in the atmosphere, but for different reasons. Under certain conditions individual molecules come together and form particles -- a chemical soup.
In the city, air pollution may be caused by cars, buses and airplanes, as well as industry and construction. Ground-level ozone is created when engine and fuel gases already released into the air interact when sunlight hits them. Ozone levels increase in cities when the air is still, the sun is bright and the temperature is warm.
HOW FOG HELPS: Collett has found that, although radiation fog can create new airborne particles, it can also help cleanse the atmosphere by absorbing polluting airborne particles. How much it can clean the air depends on the size of the airborne particles and of the size of the water droplets in the fog, as well as the depth the duration of the fog.
- Stay indoors as much as you can during days when pollution levels are high.
- If you must go outside, limit outside activity to the early morning hours or wait until after sunset. Sunshine drives up ozone levels.
- Don't exercise or exert yourself outdoors when air-quality reports indicate unhealthy conditions. The faster you breathe, the more pollution you take into your lungs.