Water vapor is removed from the atmosphere during precipitation and returns by evapotranspiration. The concentration of the water vapor varies in the atmosphere depending on the place and time of year. The concentration of water vapor is greatest over the oceans and tropical rain forest. Carbon Dioxide Carbon dioxide is the fifth most abundant gas in the atmosphere. Carbon dioxide enters the atmosphere during volcanic eruption, biomass and fossil fuel combustion, cement manufacturing and deforestation.
Carbon dioxide is removed from the atmosphere during photosynthesis and by dissolving in the oceans.
In the oceans, some of the carbon dioxide reacts with water to form carbonic acid. Ozone Ozone is a natural component of the atmosphere. It consists of 3 atoms of oxygen. Ozone is an unstable molecule which readily breaks down into molecular oxygen and 1 other atom. Harmful effects of ozone depletion to humans include risks of skin cancer, cataracts, and adverse effects on the immune system.