Evaporation
Volatile organic compounds (VOCs) enter the atmosphere by evaporation. VOCs evaporate
fromhuman-madesubstances, suchaspaintthinners, drycleaningsolvents, petroleum, wood
preservatives, and other liquids. Naturally occurring VOCs evaporate off of pine and citrus
trees. The atmosphere contains tens of thousands of different VOCs, nearly 100 of which
are monitored. The most common is methane, a greenhouse gas. Methane occurs naturally,
but human agriculture is increasing the amount of methane in the atmosphere.
Lesson Summary
- Industrial pollution causes health problems and even death, though the Clean Air Act
has decreased these health problems in the United States by forcing industry to clean
their emissions. - The increase in motor vehicles in arid cities has increased ozone and other secondary
pollutants in these regions. - Burning fossil fuels is the greatest source of air pollution.
- Biomass burning is also a large source, especially in places where slash-and-burn agri-
culture is practiced.
Review Questions
- What is the difference between the type of smog experienced by cities in the eastern
United States and that found in Southern California? - London has suffered from terrible air pollution for at least seven centuries. Why is the
city so prone to its famous “London fog?” What did London do to get rid of its air
pollution? - Imagine two cities of the same size with the same amount of industrialization and the
same number of motor vehicles. City A is incredibly smoggy most of the time and City
B usually has very little air pollution. What factors are important for creating these
two different situations? - What might be a reason why the city of San Francisco and its metropolitan area not
on the list of smoggiest cities for 2007? - Why are naturally-occurring substances, like particulates or carbon dioxide, sometimes
considered pollutants? - How does ozone form from vehicle exhaust?
- What are the necessary ingredients for ozone creation, excluding those that are readily
available in the atmosphere? Why could there be a city with a lot of cars but relatively
little ozone pollution? - Some people say that we need to phase out fossil fuel use and replace it with clean
energy. Why is fossil fuel use becoming undesirable?