Performance of a New Commercial Electrical Mobility Spectrometer

Abstract

A commercial electrical mobility spectrometer (Grimm 5.4-900 DMA and Grimm 5.403 CPC) was examined with respect to size, concentration and time-dependent responses of the CPC, the transfer function of the DMA, as well as the performance of the data inversion algorithm. For comparison with previously published results, the responses were also measured for two other commercial CPCs (TSI Model 3010 and TSI Model 3022).All measurements were performed using sodium chloride aerosol produced by an atomizer, except for size-dependent counting efficiency measurements, where an evaporation and condensation method was used to produce particles down to a size of 2 nm. The concentration-dependent CPC counting efficiency was measured against a reference instrument working in the single particle count mode following dilution. The CPC time response was evaluated for monodisperse aerosol by measuring the step response using a solenoid valve technique. The transfer function of the Grimm DMA 5.4-900 was determined between 10 and 100 nm with two verified identical DMAs in series following the approach of Fissan et al. Measured tandem-DMA responses were compared to simulated responses based on the diffusion-broadened transfer function of Stolzenburg to define the factors influencing resolution. Finally the data inversion algorithm was tested by comparison with other devices.

Distinguishing between aggregates and agglomerates of flame-made TiO2 by high-pressure dispersion

“…An aerosol was prepared by passing the suspension through a Collison nebulizer [22] followed by a silica-gel diffusion dryer. The aerosol was then classified with a differential mobility analyzer (DMA; Model Grimm 5.4-900 [23]) to obtain singly charged aerosol particles with a narrow size distribution. To further increase monodispersity, the small fraction of larger particles with multiple charges always present in DMA classified aerosols was removed with an impactor positioned upstream of the DMA.…”

“…To further increase monodispersity, the small fraction of larger particles with multiple charges always present in DMA classified aerosols was removed with an impactor positioned upstream of the DMA. An aerosol stream with a constant flow rate of 0.3 l/min was drawn into a condensation particle counter (CPC; Model Grimm 5.403 [23]) using its internal pump. The particle number concentration was always b10 4 cm − 3 so that only the more accurate, single particle count mode [23] of the CPC was used.…”

Particle deposition from aerosol flow inside a T-shaped micro-mixer

“…The monodisperse aerosol flow is split; one part is fed directly into one branch of the T-mixer, whereas the other is passed through a high-efficiency particle filter before entering through the opposite branch of the mixer. Both flows then recombine and are drawn through the device with a constant flow rate of 0.3 l min −1 , using the internal pump of the attached condensation particle counter (CPC; Model Grimm 5.403 [6]), which is capable of counting particles down to a size of 7.5 nm. The particle number concentration used was always below 10 4 cm −3 , so that only the more accurate single particle count mode of the CPC was used [6].…”

“…Both flows then recombine and are drawn through the device with a constant flow rate of 0.3 l min −1 , using the internal pump of the attached condensation particle counter (CPC; Model Grimm 5.403 [6]), which is capable of counting particles down to a size of 7.5 nm. The particle number concentration used was always below 10 4 cm −3 , so that only the more accurate single particle count mode of the CPC was used [6]. Tubes of equal length were used for the concentration measurements before and after the mixer, to minimize errors resulting from any particle losses inside the ducts.…”

“…The somewhat larger vitamin-E (tocopherol acetate) droplets in the size range from 300 to 900 nm were produced with the same nebulizer, but without subsequent drying. The aerosol was then classified with a differential mobility analyzer (DMA; Model Grimm 5.4-900 [6]) to obtain singly charged aerosol particles with a narrow size distribution. To further increase the monodispersity, the small fraction of larger particles with multiple charges always present in DMA classified aerosols [7] was removed with an impactor (not shown in figure 1) positioned upstream of the DMA.…”