Comparison of two particle-size spectrometers for ambient aerosol measurements

Abstract

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 epidemiological studies. Since there is no single instrument available for the measurement of the particle-size distribution over the full range of the fine fraction (diameter <2.5 μm) of the atmospheric aerosol, two instruments, the mobile aerosol spectrometer (MAS) and the electrical aerosol spectrometer (EAS), have been tested in a side-by-side comparison measuring ambient aerosol for a time period of six weeks in spring 1996 in the city of Erfurt, Germany. Furthermore, total particle number concentration measured by a condensation particle counter (CPC) and mass concentrations PM 10 and PM 2.5 were determined. Both spectrometers, MAS and EAS, are based on electrical mobility measurements for particles <0.1 μm and <0.5 μm, respectively, while MAS applies optical particle spectrometry and EAS applies again electrical mobility analysis for particles up to 2.5 and 10 μm, respectively. 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 – 2.5 μm. Hourly mean number concentrations of each size range observed during the six week comparison was: 2.6×10 4±19500 (2.48×10 4±1.79×10 4), 3.1×10 3±1.5×10 3 (4.1×10 3±2.0×10 3), 50±45 (1.9×10 2±1.2×10 2) cm −3 for MAS (EAS), respectively. Both aerosol spectrometers followed the variations of the ambient aerosol in a similar manner and yielded almost identical results for particle number concentrations of particles with diameters smaller than 0.5 μm. Furthermore, the total particle number concentration derived from MAS and EAS measurements (29000±20000; 29000±19000 cm −3) is well comparable with the number 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 PM 2.5 measurements are suitable to reliably characterize size-distribution parameters of number and mass concentration of ambient aerosols.