Hydrocarbons are produced when fossil fuels are burned. They are also released naturally from vegetation. Hydrocarbons react with other chemicals to form smog. Ozone is formed when hydrocarbons and nitrogen oxide are mixed in the air. There are two types of ozone.
Good ozone is the upper atmosphere, high above the Earth.
Bad ozone forms the smog found in the lower atmosphere where people live and breathe. The two kinds of ozone, generally, never mix. The ozone affects the respiratory system and can be harmful to people with asthma, bronchitis, or emphysema. It also reduces the effect the immune system has on animals. Ozone also damages crops, plants, trees, and vegetables, as well as building and other man made structures.