Assessing the contribution of water to the mass closure of PM10

The data obtained during a number of field studies aimed at determining the chemical composition of atmospheric particulate matter (PM) have shown that the measurement of the main PM components (main elements, ions, elemental carbon, organic carbon) was generally sufficient to obtain a reasonable mass closure. Notwithstanding, a wide gap between PM mass concentration and reconstructed mass was observed in two peculiar environmental conditions: desert dust intrusion and severe atmospheric stability episodes characterized by very high ammonium nitrate concentration. In these two cases, the mass closure improved significantly by adding the concentration of PM bound water. Water was determined by using a coulometric Karl Fisher system equipped with a controlled heating device; the method was able to separate different water contributions released in different temperature ranges from 50 to 250 degrees C.