A novel form of diffusion battery.

A novel form of diffusion battery uses a series of 635-mesh screens instead of the customary cluster of circular tubes or holes. Fifty-five screens are arranged in series so that the amount of aerosol penetrating through different numbers of screens can be measured with a condensation nuclei counter. This "filter stack" must be calibrated because theory is not available to calculate the performance of such screens with sufficient accuracy. For calibration a polydisperse aerosol such as ambient or silver aerosol is used to compare the performance of the screens with that of the cluster-tube and collimated-holes diffusion batteries, whose performance is known from theory. It was observed that a given number of screens is equivalent to a given number of batteries independent of the size or size distribution of the aerosol. This filter stack is very compact and light in weight (0.9 kg). It is particularly useful for measurements in the field.