Analysis of exhausts emitted by i.c. engines and stationary burners, by means of u.v. extinction and fluorescence spectroscopy

Optical investigations of the exhausts emitted by internal combustion (i.c. ) engines and a stationary burner were performed, in order to assess their relative role as sources of organic matter to the atmosphere. Extinction sp ectra of air-diluted exhausts in the 200-400 nm u.v. band reveal the expect ed existence of gaseous trace-species (NO, NO2 and SO2) and carbonaceous pa rticulate matter (soot). In addition. after subtracting the absorption cont ribution from known species, a strong residual absorption band remains belo w 250 nm, which is attributed to organic aromatic matter, involving no more than two aromatic rings. A set of ex situ extinction and laser induced flu orescence (LIF) experiments were carried out on condensed combustion-water samples. Extinction measurements from the water samples show absorption spe ctra similar to those observed from air-diluted samples, which are attribut ed to low volatility organic compounds, as they are trapped in the condense d phase. Combining the indications of extinction data for both air-diluted and condensed samples, it is suggested that the absorbing species might be molecular clusters of one/two aromatic rings. LIF spectra from condensed sa mples evidence two fluorescence bands, centered above 300 and 400 nm, respe ctively, whose intensities correlate with the combustion regimes. Analogous optical analysis on rain samples, collected in an urban area, showed that rain absorption and fluorescence spectra are similar to those found in cond ensed exhaust samples, which is consistent with the prevailing contribution of i.c. engines to the urban air pollution. The combined experimental data suggest that the absorbing and fluorescent species trapped in the condense d samples are organic (aromatic) compounds, involving mostly one-two aromat ic rings structural units, since they do not absorb above 250 nm. The overa ll molecular weight of the trapped material is likely heavy as they show lo w volatility. (C) 2001 Elsevier Science Ltd. All rights reserved.