Ricerc@Sapienza

The thermal-ramp Karl-Fisher method (tr-KF) for the determination of PM-bound water has been applied
to size-segregated PM samples collected in areas subjected to different environmental conditions
(protracted atmospheric stability, desert dust intrusion, urban atmosphere). This method, based on the
use of a thermal ramp for the desorption of water from PM samples and the subsequent analysis by the
coulometric KF technique, had been previously shown to differentiate water contributes retained with
different strength and associated to different chemical components in the atmospheric aerosol.
The application of the method to size-segregated samples has revealed that water showed a typical
mass size distribution in each one of the three environmental situations that were taken into consideration. A very similar size distribution was shown by the chemical PM components that prevailed during
each event: ammonium nitrate in the case of atmospheric stability, crustal species in the case of desert
dust, road-dust components in the case of urban sites.
The shape of the tr-KF curve varied according to the size of the collected particles. Considering the size
ranges that better characterize the event (fine fraction for atmospheric stability, coarse fraction for dust
intrusion, bi-modal distribution for urban dust), this shape is coherent with the typical tr-KF shape
shown by water bound to the chemical species that predominate in the same PM size range (ammonium
nitrate, crustal species, secondary/combustion species - road dust components).