HOW WE SMELL: A smell is the sensory response to the complex mixtures of chemicals in the air around us, called odorants. We are able to sense these chemicals because they bind to protein receptors that line the cells in our nose. Each kind of receptor can only detect specific chemical compositions, producing the sensation of different smells. These receptor proteins are produced from about 1,000 different genes: almost 3 percent of our total gene count.
THE NOSE KNOWS: Our sense of taste is partially enhanced by smell, which is why food may taste bland when we have a cold that blocks the nasal passages. Nerve receptor cells within the nose detect odors carried into the organ by air, and transmit signals to the brain through the olfactory nerve.
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.
The American Geophysical Union and the American Meteorological Society contributed to the information contained in the TV portion of this report with support from the Camille and Henry Dreyfus Foundation, Inc.