Environmental Science / Unit 7: Air Pollution and Climate
7.1 The Atmosphere and Air Pollutants
Notes
Earth's atmosphere is about 78% nitrogen, 21% oxygen, and less than 1% argon, carbon dioxide, and other gases.
- Layers from the ground up: troposphere (weather, where we live), stratosphere (ozone layer), mesosphere, thermosphere.
- Primary pollutants are emitted directly (soot, $SO_2$, CO). Secondary pollutants form from reactions in the air (ground-level ozone, acid rain).
- The EPA tracks six criteria pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide ($NO_2$), ground-level ozone ($O_3$), particulate matter (PM), and sulfur dioxide ($SO_2$).
- Sources: burning fossil fuels in vehicles and power plants, industry, and wildfires. Particulate matter such as $PM_{2.5}$ (under 2.5 micrometers) enters the lungs and bloodstream.
- The Clean Air Act (1970) gave the EPA authority to set air quality standards. Lead was removed from gasoline and acid-rain-causing $SO_2$ has fallen sharply since.
- Example: a car's exhaust releasing CO is a primary pollutant.
Practice
In which layer of the atmosphere does weather occur?
The troposphere is the lowest layer, where clouds and weather form.
Ground-level ozone is classified as a secondary pollutant because it:
Ozone at ground level is made when sunlight reacts with $NO_x$ and VOCs.
Which pair are both EPA criteria pollutants?
CO and $SO_2$ are among the six regulated criteria pollutants.
Ready for more? Take the Unit 7 test.