The best known number of a class of photochemical oxidizing agents known as the peroxy acetyl nitrate (PAN). It is formed when ozone reacts with hydrocarbons. These are commonly found in photochemical smog. PAN attacks plants, causing spotting and discolouration of leaves, desctuction of flowers and death of plants. In human beings PAN causes red, itchy, runny eyes, irritated throats and cardiorespiratory problem.