High School Earth Science: Human Actions and the Atmosphere - Effects of Air Pollution — Flashcards

Air pollution can affect lung development and is implicated in the development of emphysema, asthma, and other respiratory diseases, such as chronic obstructive pulmonary disease (COPD). Increases in asthma prevalence and severity are linked to urbanization and outdoor air pollution.

Acid rain is caused by sulfur and nitrogen oxides emanating from power plants or metal refineries. Tall smokestacks allow the emissions to rise high into the atmosphere and travel up to 1,000 km (600 miles) downwind. As the pollutants move, they combine with water vapor in the atmosphere to form sulfuric and nitric acids. The acid droplets form acid fog, rain, or snow; or they may be deposited dry. Most typical is acid rain.    
Acid rain is rainwater that is more acidic than normal rainwater. Acidity is measured on the pH scale. Neutral substances have a pH of 7.0. Acidic substances have lower pH values, and basic (or alkaline) substances have higher pH values. Normal rain is somewhat acidic with a pH of 5.6. To be considered acid rain, rainwater must have a pH of less than 5.0. A small change in pH represents a large change in acidity. For example, rain with a pH of 4.6 is 10 times more acidic than normal rain with a pH of 5.6, and rain with a pH of 3.6 is 100 times more acidic than normal rain.    
Acid precipitation ends up in soil and bodies of water. Some forest soils in the northeastern U.S. that receive a lot of acid rain are five to ten times more acidic than they were two or three decades ago. Acid rain that soaks into soil strips the soil of metals and nutrients. Soils may no longer have enough nutrients for plants to grow. Runoff from the soils carries the metals and nutrients to streams and lakes, and it makes these bodies of water even more acidic.    
When lakes become too acidic, aquatic organisms die off. No fish can live if the pH of the water drops below 4.5, and organic material also cannot decay. Wildlife that depends on the lakes for drinking water may suffer population declines.    
Plants—including food crops—that are exposed to acids in soils and rainwater become weak. They are more likely to be damaged by bad weather, insect pests, or disease. Snails and some other small soil organisms die in acid soils, so many birds do not have as much food to eat. Young birds and mammals do not build bones as well and may not be as strong. Eggshells may also be weak and break more easily.