Medi Aria - adjunct professor of biological sciences at OCCC, Oklahoma City, USA
Ehsan Azami - junior year student in pharmaceutical chemistry at Azad University of Shahrood

Two types of ozone occur on planet Earth, the good ozone in the upper levels of the atmosphere and the bad ozone in the troposphere or simply at ground levels. Ozone is one of the main components of the photochemical oxidants that is produced by the action of nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Photochemical oxidants also act as secondary pollutants. Ozone in troposphere is produced either as free radicals or chain structure. The main source for oxides of nitrogen in the troposphere is the burning of the fossil fuels. Nitrogen dioxide (NO2) is a major contributor for production of tropospheric ozone. In the presence of more than 10 ppt of NO2 several oxidants such as nitric acid (HNO3), per oxy-acetyl nitrate, ozone, etc. are produced. In the troposphere NO2 can undergo photolysis with light waves in the range of 300-400 nm. In the polluted troposphere they react with NO producing organic oxy-radicals and NO2..NO2 subsequently photolyses leading to O3 formation