Is benzene a precursor for secondary organic aerosol?

It is currently assumed that benzene contributes only negligibly to secondary organic aerosol formation in the atmosphere. Our understanding of the capacity of benzene to generate secondary aerosols is based on the work of Izumi and Fukuyama (Atmos. Environ. 1990, 24A, 1433) in which two photosmog experiments with benzene in the presence of NOx were performed and no particle formation was observed. In contrast to the observations of Izumi and Fukuyama, experiments performed in the EUPHORE large outdoor simulation chamber have clearly shown aerosol formation during the photochemical oxidation of benzene in various NOx regimes. The maximum aerosol yields of 8-25% on a mass basis are comparable to yields obtained during the photochemical oxidation of other aromatic compounds under similar conditions. In addition, a density of 1.35+/-0.04 g/cm3 for the secondary organic aerosol from the benzene photochemical oxidation in the presence of NOx has been determined through the simultaneous measurement of aerosol volume and aerosol mass using two independent measurement techniques. Comparing the results in the present work with previous findings underscores the strong influence that the NOx content in the system has on aerosol formation during the photochemical oxidation of aromatic hydrocarbons and the importance of performing experiments with NOx concentrations relevant to the atmosphere.