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.
HEALTH TIPS:
- 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.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV version of this report.