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Overview

We take it for granted until raging fires fill it with smoke, burning our eyes and throat. Sometimes following a diesel truck will choke off our oxygen supply, or the smell of sweaty gym socks left in a locker too long will make us gag. Then we realize that air is a complex mixture of compounds. The major components are nitrogen (78%) and oxygen (21%), but air also contains smaller amounts of many other gases including carbon dioxide, which you have heard about for its roles in photosynthesis and global warming. However, air is not just a mixture of gases; it also contains atmospheric aerosols. Atmospheric aerosols are particles of liquids or solids that are small enough to float in the air. The particles can come from natural sources, including pollen from flowers, dust blowing over the desert and ash from wildfires and volcanoes. Even the ocean waves create aerosols—sea salt spray. Aerosols can also be human made (anthropogenic), such as particles from factory smoke, auto emissions and slash-and-burn agricultural practices.

These particles are most numerous near the Earth's surface, but rising currents of air can carry them to great heights. Atmospheric aerosols can therefore travel long distances—literally around the world. Since these particles know no borders, international cooperation is essential in any measures designed to control them.

Why This Science Matters

The aerosols in our air can give it a hazy appearance. Everyone would rather see a beautiful mountain than atmospheric aerosols! Airborne particles cause more serious problems than just blocking the view though. People who suffer from hay fever know about natural aerosols. They may check the daily pollen count in the newspaper before exercising outdoors. Approximately 20 million Americans have asthma, and the prevalence of asthma has increased dramatically in recent decades. The cause of this increase is not well understood, but aerosols, both natural and anthropogenic, create serious challenges for people with asthma or other lung problems, and children growing up in heavily polluted cities have lowered lung function.

In addition to their health effects, atmospheric aerosols affect weather and climate in complex ways. For example, aerosols may absorb or reflect incoming sunlight. They can also play a role in cloud formation. Since global warming will have far reaching effects on human health as well as the welfare of all organisms on Earth, it is important to understand the effects of atmospheric aerosols on climate.

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Teacher Credit: Lesson developed by Ann Marie Wellhouse, founder of River Valley Charter School, who currently teaches classes in science leadership and science investigations and has also taught biology and earth science.