Levels of volatile organic compounds in ambient air of Rome

Hydrocarbons are a significant component in urban air because of combustion, solvent and fuel evaporation and tank leakage; most of aromatic compounds are considered as toxic air contaminants (e.g. benzene) or potential toxic air contaminants (e.g. toluene, xylenes). Further, the NMHCs play a key role in the formation of photochemical air pollution. They are considered as precursors for ozone production at the ground level when the sunlight and nitrogen oxides are present. NMHCs and aromatic hydrocarbons participate in the formation of urban and suburban photochemical smog with their concentrations influencing greatly the total ozone in different percentage [1]. Derwent et al. [2] were the first to determine that m-xylene, trimethylbenzenes and C3-C4 alkenes produce more ozone than ethylene. In this paper, we report the results obtained during an intensive measurement campaign in wintertime. The air quality analysis was conducted by two different ways. About 50 air samples were taken by canisters in 4 different locations in Rome during 3 days to investigate the non-methane and aromatic hydrocarbon composition; at the same time, automatic analyzers and Differential Optical Absorption Spectrometry (D.O.A.S.) investigated traditional atmospheric pollutants like ozone, nitrogen dioxide, nitrous acid, carbon monoxide, formaldehyde, benzene and toluene in downtown Rome. Finally, we calculated the percentage contribution of each determined VOC to ozone formation in the ambient air of Rome, comparing these values with other studies reported in literature. The results obtained show that the m-xylene, the toluene and 1,2,4- trimetilbenzene are the compounds that compete in better percentage to the formation of ozone in Rome. Further, in the same period the trends of benzene, toluene, CO, NO and PAH are decreased, expecially because of introduction of both the green fuel and the autovehicular catalytic pot. But, even if the pollutant levels are decreasing, the sources are still the same and, in particular, the emission from the incomplete combustion of LPG is the most important source of pollution in Rome. [1] A. Monod, B.C. Sive, P. Avino, T. Chen, D.R. Blake, F.S. Rowland, Atmos. Environ. 35 (2001) 135-149. [2] R.G. Derwent, M.E. Jenkin, S.M. Saunders, Atmos. Environ. 30 (1996) 181-199.