Comparison of two particle-size spectrometers for ambient aerosol measurements

There is an ongoing debate on the question which size fraction of particles in ambient air may be responsible for human health effects observed in epi demiological studies. Since there is no single instrument available for the measurement of the particle-size distribution over the full range of the f ine fraction (diameter < 2.5 mu m) of the atmospheric aerosol, two instrume nts, the mobile aerosol spectrometer (MAS) and the electrical aerosol spect rometer (EAS), have been tested in a side-by-side comparison measuring ambi ent aerosol for a time period of six weeks in spring 1996 in the city of Er furt, Germany. Furthermore, total particle number concentration measured by a condensation particle counter (CPC) and mass concentrations PM10 and PM2 .5 were determined. Both spectrometers, MAS and EAS, are based on electrica l mobility measurements for particles < 0.1 mu m and < 0.5 mu m, respective ly, while MAS applies optical particle spectrometry and EAS applies again e lectrical mobility analysis for particles up to 2.5 and 10 mu m, respective ly. Both instruments proved to be reliable during this comparison providing data availability of > 94%. To compare the spectral data, particle numbers were integrated within three size ranges: 0.01 - 0.1, 0.1 - 0.5, 0.5 - 25 mu m. Hourly mean number concentrations of each size range observed during the sig week comparison was: 2.6 x 10(4) +/- 19500 (2.48 x 10(4) +/- 1.79 x 10(4)), 3.1 x 10(3) +/- 1.5 x 10(3) (4.1 x 10(3) +/- 2.0 x 10(3)), 50 +/- 45 (1.9 x 10(2) +/- 1.2 x 10(2)) cm(-3) for MAS (EAS), respectively. Both a erosol spectrometers followed the variations of the ambient aerosol in a si milar manner and yielded almost identical results for particle number conce ntrations of particles with diameters smaller than 0.5 mu m Furthermore, th e total particle number concentration derived from MAS and EAS measurements (29000 +/- 20000; 29000 +/- 19000 cm(-3)) is well comparable with the numb er concentration derived from an integral counting CPC (31100 +/- 22000 cm( -3)). The results of this side-by-side comparison suggest that MAS and EAS together with PM2.5 measurements are suitable to reliably characterize size -distribution parameters of number and mass concentration of ambient aeroso ls. (C) 1999 Elsevier Science Ltd. All rights reserved.