The air in our lower atmosphere is a dynamic,
constantly shifting mixture of gases, liquid droplets, and
small particles. It swirls and eddies around the globe
like the water in an ocean, with winds and weather
patterns resulting from this movement. Air isn’t as light
as it seems, either. A column of air one foot square
and extending from sea level to the outer limit of the
atmosphere would weigh nearly one ton. And contrary
to what one might expect, the air we breathe in the
lower atmosphere is not primarily composed of oxygen.
Instead, it contains 78 percent nitrogen, 21 percent
oxygen, and less than one percent gases like argon
and carbon dioxide. Unfortunately, it can also contain
substances that are unhealthy for us to inhale.
In the Bay Area, as in the entire state of California, a certain amount of air pollution comes from stationary industrial sources, such as refineries and power plants. But a greater percentage of harmful air emissions come from cars and trucks, construction equipment, and other mobile sources. California has more cars per household (1.8) than any other state, along with a thriving business economy and a continually expanding population. All of these factors contribute to the state’s air quality challenges.