Atmospheric pollution has many causes, some of which are more from nature than from human activity; others of which are predominantly from human activity. These causes are classified into anthropogenic (or human), and natural, and the natural causes are suprising to many who have focused on auto exhaust, hair spray and other man made particulates.
The major problem with particulate, liquid and gaseous atmospheric pollution is in the chemical reactions that occur, converting normal substances into harmful or toxic substances, or creating such a mass of solid matter that living organisms are affected.
Carbon monoxide is the major pollutant and is mostly from natural causes. As living things decompose and gas off, releasing methane which oxidizes and converts to CO.secondly, the decaying chlorophyll and pigment of plants contributes to CO. Most of the human contribution is from automobiles that burn fossil fuels. Whatever the source, carbon monoxide is believed to have minimal threat or impact on living things.
Nitrogen oxide is not really considered to be either a threat or a polllutant, but is contributed by soil decomposition, bacteria and lightening.
The sulfur oxides come primarily from decomposing organic matter, including burning of coal, which is the major anthropogenic contribution. But coal comes from organic matter. The most alarming oxide is sulfur trioxide which interacts with atmospheric moisture to produce sulfuric acid, or acid rain. But the sulfur oxides do not stay for long in the atmosphere.
The hyrdocarbons include methane, which oxides into CO. There are many, many hydrocarbons. After carbon monoxide, hydrocarbons are the most prevalent pollutants. Most hydrocarbons are from natural sources, with anthropogenic contributions coming from petroleum related activities.
Suspended particulate matter is the final atmospheric pollutant. Amazingly, the biggest contribution to atmospheric particulate pollution comes from the oceans, where tiny bubbles release microscopic salt crystals into the atmosphere. Then there are volcanic eruptions, dust storms, fires and other natural contributions. Anthropogenic contributions in the form of particulate matter are less than the natural contributions through fossil fuel burning, vehicles, and stone work.
The vast amount of work in the anthropogenic area concerns reducing auto emissions and fossil fuel burning, and there is much to be done. But as there are more people, there will be more animals and more plants and more methane. Conservation in the area of man made chemicals, processes and reactions must continue in order to allow nature to do its thing and to reduce our footprint on the atmosphere!