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, includin g NO2, HNO2, HNO3 and their mixtures, was studied in simulated atmosphere u nder 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 rapid ly when it was catalyzed by a mixed gas of HNO2 and HNO3, and even faster t han the sum of what individually catalyzed by HNO3 and HNO2 gases. These re sults imply that the nitration of polycyclic aromatic hydrocarbons via reac tion with the mixed gas of NO2, HNO3 and HNO2 may contribute to the nightti me formation of nitro polycyclic aromatic hydrocarbons in the atmosphere.