Heterogeneous nitration reactions of polycyclic aromatic hydrocarbons and n-hexane soot by exposure to NO3/NO2/N2O5

Although heterogeneous reactions of polycyclic aromatic hydrocarbons (PAHs) with atmospheric oxidants may be important loss processes for PAHs, our understanding of their kinetics and products is incomplete. A product study of the reaction of two PAHs (i.e., anthracene and pyrene) and n-hexane soot with NO3 and N2O5 using a variety of analytical techniques (XPS, DRIFTS, GC-MS, optical absorption) was undertaken. The goal was to characterize the products of these heterogeneous nitration reactions to aid in reaction mechanism development. NitroPAHs were found to be the products of the nitration of anthracene and pyrene whereas evidence of both nitro and carbonyl functional groups were observed on the surface of n-hexane soot samples following exposure to a mixed flow of NO3 and N2O5. Absorption experiments indicate that the nitration of PAHs alter the optical properties of the particles to which they are adsorbed, giving rise to absorption intensity in the near UV and visible portions of the spectrum.