Ozone is the major component in what we know as smog at ground level. Ozone is not emitted directly into the air but is produced in the lower atmosphere as a result of chemical reactions between oxygen and oxides of nitrogen in the presence of sunlight, especially in warm weather. This reaction normally results in a constant cycle where ozone is created and immediately broken down back into oxygen and NOx. However, hydrocarbons and other VOCs exist in the air which prevent ozone from breaking down, therefore increasing ozone concentrations. In the body, ozone reacts with lung tissue, causing inflammation of the lungs. Ozone can cause harmful changes in breathing passages, decrease the lungs' working ability and cause coughing and chest pains. Even healthy people are found to be sensitive to ozone exposure.