FTIR spectral analysis of PM10 and PM2.5 particulate matter over the urban area of Palermo (Italy) during normal days and Saharan events

The principal sources of particulate matter in Palermo urban area are gasoline and diesel-powered vehicles, domestic heating, resuspension of soil dust and a geogenic source which includes soil erosion, marine aerosol and sporadic Saharan events. Annual average PM10 and PM2.5 concentrations result 27.8±9.8 and 21.3±5.1g/m3. The highest mass levels, 246 and 65 g/m3 respectively for PM10 and PM2.5, were observed during Saharan events. For the present study, which uses the ATR-FTIR spectroscopy to provide insights on the chemical composition of airborne particulate matter, a total of 89 filters were collected: 13 PM10 filters from a sub-urban background station, 36 PM10 and 40 PM2.5 filters from a sampling site exposed to heavy traffic. ATR-FTIR spectra were aquired with a Tensor 27 (Bruker Optics) FTIR spectrometer operating in the infrared (370-7500 cm−1) region. After correction for the background spectrum all the analyzed spectra showed vibrational frequencies at 616 and 1088, 813 and 1352, 1414 cm-1, corresponding to SO42-, NO3- and NH4+ ions, respectively. The simultanea presence of these ions, confirmed by LC and UV-VIS techniques, suggests the formation of secondary particulate of ammonium nitrates and sulphates. The peak at 778 cm-1 was attributed to geogenic CO32- ions derived from erosion of local carbonate rocks. PO43- ions, identified by the peak at 535 cm-1, were detected in suburban samples as well as in urban samples and they are indicative of contamination from phosphate industries of North Africa although their origin from pollen grains cannot be ruled out. FTIR also identified several organic functional groups, although specific organic molecules could not be identified. The broad band in the aliphatic stretching region (2800–3000 cm-1) with sharp peaks at 2850, 2920 and 2952 cm-1, was attributed to aliphatic C-H vibrations. The urban filters exposed to SW and SE winds (from North Africa) are characterised by peaks at 913cm-1, 3620 and 3698 cm-1, indicative of OH-stretching in clay and also peaks at 3404 and 3545 cm-1 typical of gypsum.