Improved Inversion of Scanning DMA Data

Recovery of aerosol size distributions from either stepping or scanning mode differential mobility analyzer (DMA) measurements requires an accurate description of the characteristics of the DMA itself, as well as certain properties of the aerosol. Inversion of scanning DMA data is further complicated by the nonunique relationship between the time a particle exits the DMA and the time it is ultimately detected. Without an accurate description of this relationship, and an appropriate method of accounting for it, inverted distributions will be broadened and skewed relative to the true distribution. A simplified approach to inversion of scanning DMA data is described here in which adjustment of the raw data to account for the delay time distribution associated with the instrument is accomplished prior to final inversion. This provides the flexibility to utilize more accurate descriptions of the delay time distribution and the DMA transfer function than is feasible if the inversion is to be accomplished in one step as described by Russell et al. (1995). The accuracy of this procedure has been demonstrated through analysis of actual as well as test-case data.