Evolution and biogeochemical cycle of pollutants

The significance of atmospheric processes in the genesis of nitro-PAH has been
widely discussed in the last 15 years and the occurrence of these pollutants in
the air particulate collected both in developed and remote areas of the world
has been demonstrated, but no report exists verifying the possible presence of
nitro-PAH in the Antarctic. This task was undertaken in the present study,
which uses an extremely sensitive and specific analytical procedure to
investigate the composition of size-fractionated airborne particulates,
collected in the Terra Nova Bay area (Antarctica) during two-days high-volume
sampling periods. Eleven air-particulate samples and three blanks were
extracted and analyzed by gas-chromatography-electron capture negative
ion-tandem mass spectrometry. The specificity of this instrumental technique
for nitro-PAHs was assured by both the ionization method and the fixed setting
of the second mass analyzer, selectively filtering the NO2- ions (m/z 46). Only
the most volatile nitro-PAHs (nitronaphthalenes, dinitronaphthalenes,
9-nitroanthracene) were detected in the Antarctic air particulate, unlike what
is observed in temperate areas. Single nitro-PAH concentrations varied in the
1-200 fg/m3 range. These nitro-PAHs are likely to be produced by light-induced
atmospheric reactions of the corresponding PAHs, possibly transported from
other continents in the gas phase. The abundance of dinitro- with respect to
mononitro-derivatives suggests that the nitration process is efficient
relatively to the scarce availability of the substrates. Principal component
analysis allowed to cluster the blanks, clearly distinguishing them from the
samples, to recognize an interfering dinitronaphthalene and to classify the
samples, as a function of their nitro-PAH composition. Nitro-PAH distribution
proved to depend on the sampling day but not on the particle size-fraction
within the same sampling period. For two air particulate samples the analytical
data proved to be biased by sea-triggering of the sampling device.