The formation of smog was studied on the basis of the following hypothesis : when sulfur dioxide and nitrogen dioxide react each other in the atmosphere, nitrosyl-sulfuric acid will be formed at the initial stage by solar radiation in the presence of moisture or fog and then sulfuric acid will be formed by the decomposition of nitrosyl-sulfuric acid. That is,
SO₂^*⁢H₂O → H₂SO₃
H₂SO₃⁢NO₂^* → HOSO₂ONO
HOSO₂ONO → H₂SO₄⁢HNO₃
The nitric acid generated by the above reaction will react with organic peroxide and forms nitro peroxide compounds. Finally, the mixture of sulfur oxide, nitrogen oxide, organic peroxide nitro-compounds and oxidant will cause the formation of smog. A series of experiments have been performed and the results supported the above hypothesis as expected. In addition, a separate study has been carried out with regards to the air pollution in Seoul to confirm that sulfur oxide was more serious than nitrogen oxide.