Chemical Reactions That Produce Smog

N2 + O2 -> 2NO   1 - Nitrogen and oxygen directly combine inside the cylinders of the internal combustion engine producing nitrogen oxide. 2NO + O2 -> 2NO2   2 - As soon as the nitric oxide from the exhaust reaches the atmosphere, it is oxidized by oxygen molecules (the oxygen we breathe) forming nitrogen dioxide. NO2 + light -> NO + O   3 - Then ultraviolet radiation from the sun causes nitrogen dioxide to photochemically break up or decompose freeing one of the oxygen atoms leaving nitric oxide and atomic oxygen. O + O2 -> O3   4 - Atomic oxygen is very reactive. In one reaction, it combines quickly with the oxygen we breathe to produce ozone. O3 + NO -> NO2 + O2   5 - In an unpolluted atmosphere, ozone recombines with leftover nitric oxide again forming nitrogen dioxide and oxygen. This neutralizes the ozone and prevents it from building up.   6 - But when the atmosphere is polluted, unburned hydrocarbons or volatile organic compounds react with the free nitric oxides and prevent them from recombining with ozone. O3 + NO -> NO2 + O2   7 - When pollutants such as volatile organic carbons are present, they gobble up the leftover carbon monoxide before it can neutralize ozone, breaking the normal cycle. 8 - The normal cycle is broken, leaving ozone and photochemical byproducts behind. Ozone and smog continue to accumulate.  Back to Pollutants Add Up To Smog