Air pollution can be thought of as gaseous and particulate contaminants that are present in the earth’s atmosphere. Chemicals discharged into the air that directly impacts the environment are called primary pollutants. These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants. Common air pollutants, called criteria pollutants, are particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm health and the environment and cause property damage. The historical record shows that the climate system varies naturally over various time scales. In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas concentrations. Recent climate changes, however, cannot be explained by natural causes alone. Natural causes are unlikely to explain most observed warming, especially since the mid-20th century. Rather, human activities can explain most of that warming.
The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from burning fossil fuels. Greenhouse gas concentrations in the atmosphere will continue to increase unless the billions of tons of our annual emissions decrease substantially. Increased concentrations are expected to increase Earth’s average temperature, influence the patterns and amounts of precipitation, reduce ice and snow cover, as well as permafrost, raise sea levels, and increase the acidity of the oceans. These changes will impact our food supply, water resources, infrastructure, ecosystems, and even our own health. Acid rain refers to a mixture of wet and dry deposition from the atmosphere containing higher-than-normal amounts of nitric and sulfuric acids. The precursors of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion. Acid rain causes acidification of lakes and streams and damages trees and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, contributes to the corrosion of metals, and damages human health. The ozone depletion process begins when CFCs and other ozone-depleting substances (ODS) are emitted into the atmosphere. Reductions in stratospheric ozone levels lead to higher levels of UVB reaching the Earth’s surface. The sun’s output of UVB does not change; rather, less ozone means less protection, and hence more UVB reaches the Earth. Ozone layer depletion increases the amount of UVB, leading to negative health and environmental effects.
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