You learned in the first lesson of this week that Earth's atmosphere naturally contains some particulate matter. However, too many particulates in the atmosphere is harmful to the respiratory systems of animals, and damaging to plants. Particulate matter includes liquid droplets and solid materials suspended in the air. This can include substances such as smoke, dust, ash, and pollen. Globally, natural sources of particulate matter - including volcanic eruptions, forest fires, ocean spray, and wind-blown dust - outweigh human-caused particulate pollution. However, human activities account for a much larger percentage of particulate pollution over urban areas. Smoke from factories, exhaust from automobiles, as well as mining and construction activities that stir up dust, are some common sources of particulate matter pollution near cities.

Particle size is important when discussing the health effects of particulate matter pollution. Smaller particles of harmful materials are more easily trapped in your lungs; sometimes they can even make it into your bloodstream. Particulate matter pollution can cause asthma, coughing, difficulty breathing, decreased lung function, and early death in people with respiratory or heart problems.

Source: Particulate Matter, Health & Environment. EPA. Retrieved from http://www.epa.gov/PM/health.html on September 30, 2010.