We use different types of fuels as a source of chemical energy. Especially wood , natural gas , petroleum etc. we are constantly using. It is very important to purify all these fuels. When these fuels are burned in the presence of low air, carbon monoxide is produced along with carbon dioxide , which is a poisonous gas. These are extremely harmful to our body. The fuels that are found in nature are basically impure. It is mixed with various compounds like Nitrogen , Sulfur , Phosphorus etc. That is why it is necessary to purify these fuels in sufficient quantity before releasing them in the market. When it burns without refining, the oxides of these elements are released into the air along with the carbon dioxide gas. These oxides combine with rainwater to form acids. As a result, these acids are mixed with the rain that occurs then. This rain is called acid rain. This acid rain is very harmful to the environment. The plants die. The water in the pond becomes acidic. As a result, it is difficult for fish and other aquatic animals to survive. Vehicle fumes also contain carbon monoxide , nitrous oxide and unused fuels (such as methane). In the presence of sunlight, they produce various toxic gas fumes through various chemical reactions. These are called ' photochemical smog ' . Various components of photochemical fumes deplete the ozone layer ( O3) in the atmosphere . Ozone protects the earth from the sun's ultraviolet rays. Therefore, if this level of erosion is caused, the people of the world will be endangered.