Air Pollution and Atmospheric Visibility
Have you ever spent time in a large city? If so, the odds are you’ve seen the sky engulfed in a brownish-yellow or grayish-white haze due to air pollution. Such haze can reduce visibility from miles (kilometers) to yards (meters). Mountains or buildings once in plain sight can suddenly be blocked from view.
Air pollution that reduces visibility is often called haze or smog. The term smog originally meant a mixture of smoke and fog in the air, but today it refers to any mixture of air pollutants that can be seen. Smog typically starts in cities or areas with many people, but because it travels with the wind, it can appear in rural areas as well.
One consequence of smog over any given area is that it can change the area’s climate. Certain dark particles, such as carbon, absorb solar radiation and scatter sunlight, helping produce the characteristic haze that fills the skies over the world’s megacities. This haze reduces the amount of the Sun’s energy reaching the Earth’s surface, sometimes by as much as 35 percent.
A reduction in sunlight may not be the only thing air pollution inhibits. Some research has supported the idea that certain air particles are altering rainfall patterns as well. Although particles in the air form the nucleus that attracts cloud moisture into water droplets, specks of soot or black carbon may be too small to produce raindrops big enough to hit the ground. Since rain flushes pollutants from the atmosphere, visibility could be negatively impacted as a consequence.
Scientific field campaigns such as MILAGRO are one way scientists can research atmospheric processes to prove or disprove such ideas. For now, if rain isn't in the forecast when atmospheric visibility is low and smog is high, than wind is likely your best hope for a return to clear skies.