What are atmospheric contaminants and effect on atmosphere?

Answer 1

A contaminant would be a foreign substance that does not naturally occur without human intervention. So, for example, in the Amazon rain forest, automobile antifreeze would be a contaminant because antifreeze doesn't occur in the Amazon basin naturally. People have to bring it in and dump it there.

In the atmosphere, carbon dioxide is NOT a contaminant. Carbon dioxide occurs naturally in Earth's atmosphere, as does methane. However, chlorfluorocarbons such as Freon do NOT naturally occur in the atmosphere. Many other gases are made by humans and do not occur in nature. CFC's are the most well-known example because in 1974 two atmospheric chemists, Rowland and Melina, researched where CFC's would go once they were released into the atmosphere. They concluded that CFC's will break down, but that their separate atoms would then start eating a hole in the Earth's ozone layer, and published a paper issuing a warning.

The scientific community found the research solid and persuasive, but a number of chemical industry companies banded together to attack this research and its call for a ban on CFC's, which were very profitable. Despite the massive public relations campaign and many public statements that a ban on CFC's would hurt industry and the economy, President Carter banned CFC manufacture and use in the USA past a certain date.

In 1985 NASA was finally able to put up satellites that could track the ozone level at the Earth's poles, and found that there was indeed a growing ozone hole that was even worse that Rowland and Molina predicted. In 1987 the Montreal protocol banned CFC use worldwide. Perhaps the nations acted quickly on ozone because there was no argument that the world without an ozone layer would quickly become hostile to human existence, with a massive drop in agricultural productivity and an equally massive rise in deaths by cancer.

Some evidence says the ozone hole is now stable and even slowly closing. So humanity really dodged a bullet at the very last moment there.

The effect of any contaminant on the atmosphere depends on its chemical makeup. There is no general answer, only specific answers, as given here.