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Response functions of the ELPI impactor with normal and porous substrates are presented together with fit functions to describe particle collection. In addition to primary collection efficiency, fits for the secondary collection mechanisms, diffusion, image charge force, and space charge field are presented. Charging efficiency for different configurations is also presented. Presented response functions can be used in data reduction and inversion of ELPI data.

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The effect of nanoparticle structure on gas sensing performance is investigated. Size-selected nanostructured SnO 2 agglomerate particles for gas sensors were made by scalable flame spray pyrolysis. These particles were polydisperse ͑up to 12 m in diameter͒ and consisted of primary particles of 10 nm in grain and crystal size as measured by transmission electron microscopy, x-ray diffraction, and Berner low pressure impactor ͑BLPI͒. The effect of agglomerate size on thermal stability and sensing of ethanol vapor ͑4 -100 ppm͒ and CO ͑4-50 ppm͒ was investigated by selecting nearly monodisperse fractions of these agglomerates by the BLPI. Sensor layers made with these size-fractionated agglomerates exhibited higher thermal stability and dramatically enhanced sensitivity for both analytes than layers made with polydisperse agglomerates. This is attributed to their aggregate ͑or hard agglomerate͒ structure exhibiting small sinter necks between their constituent primary particles of tin dioxide that had also a narrow size distribution as expected for particles generated in flames. Upon further sintering of these optimally sized, nanostructured agglomerates, grain and neck growth degraded their superior sensitivity, supporting the proposed mechanism of their enhanced sensitivity: optimal primary particle necking.

This paper describes a new sampling concept for particle emission measurements. The purpose is to produce repeatable and reproducible conditions for nucleation phenomena. The exhaust is sampled and instantaneously diluted by inserting a porous tube diluter inside the tailpipe. This is carried out in order to prevent uncontrolled sample transformations in sampling lines. The sampling system was tested in size distribution measurement of light duty diesel vehicle. The tests showed a clearly bimodal size distribution with distinguished nuclei and accumulation modes.