Comparability of three spectrometers for monitoring urban aerosol

The comparability was tested of three aerosol "spectrometers", used in a pr ogram for monitoring the spectra of fine and ultrafine particles in three E uropean cities. Droplets of sebacate, solid ammonium sulfate and agglomerat es of elemental carbon were used in the tests, representing the major chemi cal and structural types of particles encountered in urban aerosol. Particl es in the ultrafine range (10-100 nm) are sized by electrical mobility (SMP S, DMPS and EAS) and the "spectrometers" gave very similar size distributio ns for these aerosols. The integrated number concentrations were on average within 20% of the directly measured total number concentrations. Particles with a size between 0.1 and 2.5 mum, in which most of the volume/mass is c oncentrated, are being differently classified in the three "spectrometers", respectively, with a low- and a high-flow LAS-X, and field charging in the EAS. The agreement between the three instruments in this size range was le ss good, which was partly caused by signal overload in the high-flow optica l sizer, which was solved using a larger threshold. A complication occurred with the elemental carbon, which was composed of highly agglomerated entit ies. Particles, sized by the mobility instrumentation as being in the range of 100-400 nm, were not detected by the optical sizers. Volume (spectra) f or ammonium sulfate deduced from the number spectra were compared with the mass (spectra) obtained with cascade impacters. The comparison was good for the LAS-Xs; the EAS overestimated volume/mass. (C) 2001 Elsevier Science L td. All rights reserved.