Introduction Atmospheric chemistry is the field in science that deals with the atmosphere and the chemical reactions occurring in it. Earth’s atmosphere that forms the immediate cover is composed of oxygen, nitrogen, carbon dioxide, methane, and other gases. The chemical reactions that happen in the troposphere making new and different chemicals have a direct impact on human beings and all other life forms on the earth. The troposphere is the first atmospheric layer and is about 7 km at the poles and 17 km at the equator. The stratosphere is the next layer of the atmosphere and is from that 7 – 17 km range to about 30 km above the earth’s surface (Wikipedia n. pag, 2007a). This layer is rich in ozone and forms a proactive layer from the sun’s ultraviolet rays. The stratosphere is followed by the mesosphere, the heterosphere, and the exosphere. Chemistry of the atmosphere As mentioned before the earth is surrounded by a blanket of gases. This blanket of gases traps energy in the atmosphere, in a similar way a man-made greenhouse does. The earth’s natural greenhouse results in a build-up of energy, and the overall warming of the atmosphere. This is called the greenhouse effect and is a natural process because of which life on earth is possible. Without this, naturally occurring greenhouse gases such as water vapor, carbon dioxide, methane, and nitrous oxide, the Earth’s surface temperature would have been very cool, and live on it could have been impossible for all of us (Earth Science n. pag). Because of the increase of greenhouse gases due to man-made activities, the enhanced effect which is caused is increasing the earth’s temperature or in other words, global warming is occurring. Besides, greenhouse gases such as CFCs are responsible for depleting the ozone layer. The ozone layer is being damaged mainly by certain industrial chemicals, vehicular pollution, and also due to ozone-depleting refrigerants, halons, and methyl bromide (ESS n. pag, 2000). A complex series of reactions occurring in the atmosphere results in the chemistry of the atmosphere. The presence of the sun’s UV rays makes these reactions more and more complex. In the troposphere, atmospheric chemistry forms ozone (a pollutant) and many highly reactive intermediates and molecules including acids, peroxides, and other undesirable products that can result in serious problems for human health and the environment. However, in contrast, stratospheric chemistry leads to the destruction of natural stratospheric ozone, our protective shield from short ultraviolet radiation at the earth’s surface (Calvert 1-12). Oxygen cycle The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere, the biosphere, and the lithosphere. Oxygen is mainly obtained as a by-product of photosynthesis. Since vast amounts of oxygen are present in the atmosphere, it is estimated that even if all photosynthesis were to cease it would still take about 2.5 million years to strip out more or less all oxygen. Much of the discussion on the oxygen cycle has focused on the question of the origin of atmospheric oxygen and its variations over geologic time. Since both photosynthesis and respiration are cyclic processes, both involving release and utilization of oxygen there is a balance established. Through the process of photosynthesis, carbon dioxide and water is broken down to convert into sugar or glucose. As a by-product of this reaction oxygen is released into