Comparability of three spectrometers for monitoring urban aerosol
Abstract
The comparability was tested of three aerosol ``spectrometers{''}, used in a program
for monitoring the spectra of fine and ultrafine particles in three European cities.
Droplets of sebacate, solid ammonium sulfate and agglomerates of elemental carbon
were used in the tests, representing the major chemical and structural types of particles
encountered in urban aerosol. Particles in the ultrafine range (10-100 nm) are sized
by electrical mobility (SMPS, DMPS and EAS) and the ``spectrometers{''} gave very
similar size distributions 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
concentrated, 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 less good, which was partly caused by
signal overload in the high-flow optical sizer, which was solved using a larger threshold.
A complication occurred with the elemental carbon, which was composed of highly agglomerated
entities. Particles, sized by the mobility instrumentation as being in the range of
100-400 nm, were not detected by the optical sizers. Volume (spectra) for 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 Ltd. All rights reserved.
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