The ozone concentration in the troposphere is directly related to the pollutants that are in the air and the time of day. For example, during the early hours of the day many pollutants are released into the air. As the day progresses, the sun becomes more overhead and the concentration of the sunlight increases. This solar radiation causes chemical reactions to occur and the primary pollutants decrease while the concentration of ozone increases. Eventually the ozone breaks back down and the process is ready to proceed the next day. [Regulation; 13(1); 31-40; 1990.] [Atmospheric Environment; v38; 2361-2371; 2004.]