Air pollution can be defined as any harmful material that is present in the earth’s atmosphere. The causes of such pollution, therefore, are many and highly varied. Some sources are natural, such as volcanism or forest fires started by lightning, while others are brought about by human activity, such as the burning of fossil fuels. While the earth does have built-in mechanisms for getting rid of air pollution, it is usually better for all living things to reduce the amount of pollutants released into the air to begin with.
The most well-known and pervasive causes of air pollution are man-made. The burning of petroleum products is a very common cause of pollution, especially in metropolitan areas. This pollution comes from chemical factors present when these fuels combust. When hydrocarbons such as gasoline are burned, they produce carbon dioxide and water vapor. Incomplete combustion leads to carbon monoxide also being created as a byproduct.
Carbon dioxide and carbon monoxide are both considered to be pollutants. Also, no fossil fuel is perfectly pure and no engine is perfectly efficient, so small particles of soot are also released into the atmosphere, along with trace amounts of other undesirable substances. Other man-made causes of air pollution include smokestack emissions from factories and power plants. The substances emitted at these sources can include sulfur dioxide and nitrogen dioxide, which are responsible for the formation of acid rain.
While man-made air pollution does present health hazards, natural sources of air pollution can be equally dangerous at times. These sources include dust picked up by wind erosion, the emission of methane by livestock, and smoke from wildfires. Volcanic eruptions are perhaps the largest single source of air pollution, natural or man-made, that humans have ever dealt with. These can produce clouds of abrasive volcanic ash and other harmful substances such as chlorine and sulfur.
Most notably, the eruption of Indonesia’s Mount Tambora in 1815 sent such a huge amount of noxious gases and particulate matter into the atmosphere, that much solar energy was effectively blocked from reaching the earth’s surface. As a result, widespread famines were suffered worldwide in 1816. Brown and red snows were also seen in Europe, due to the presence of volcanic ash in the atmosphere. A killing frost in July of 1816 also led to massive crop failures in the northeastern United States, leading to colloquial references to 1816 as “The Year Without a Summer,” and “Eighteen Hundred And Froze To Death.”