Effect of nitrous acid gas on the nitration of pyrene adsorbed on silica particles by nitrogen dioxide

Nitration of pyrene adsorbed on silica particles by various gases, including NO2, HNO2, HNO3 and their mixtures, was studied in simulated atmosphere under dark and room light conditions. Not only HNO3 but also HNO2 acted as a catalyst. The nitration of the adsorbed pyrene by NO2 proceeded most rapidly when it was catalyzed by a mixed gas of HNO2 and HNO3, and even faster than the sum of what individually catalyzed by HNO3 and HNO2 gases. These results imply that the nitration of polycyclic aromatic hydrocarbons via reaction with the mixed gas of NO2, HNO3 and HNO2 may contribute to the nighttime formation of nitro polycyclic aromatic hydrocarbons in the atmosphere.