Ss. Merola et al., Analysis of exhausts emitted by i.c. engines and stationary burners, by means of u.v. extinction and fluorescence spectroscopy, CHEMOSPHERE, 42(5-7), 2001, pp. 827-834
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.