Abstract
ABSTRACTAerosol mobility size spectrometers are commonly used to measure size distributions of submicrometer aerosol particles. Commonly used data inversion algorithms for these instruments assume that the measured mobility distribution is broad relative to the DMA transfer function. This article theoretically examines errors that are incurred for input distributions of any width with an emphasis on those with mobility widths comparable to that of the DMA's transfer function. Our analysis is valid in the limit of slow scan rates, and is applicable to the interpretation of measurements such as those obtained with tandem differential mobility analyzers as well as broader distributions. The analysis leads to expressions that show the relationship between the inverted number concentration, mean size, and standard deviation and true values of those parameters. For narrow distributions (e.g., for a mobility distribution produced by a DMA with a 1:10 aerosol:sheath air flow ratio) under typical operating conditi...
Highlights
An aerosol mobility size spectrometer system consists of an aerosol charger followed by Differential Mobility Analyzer (DMA) and an aerosol detector, usually a Condensation Particle Counter (CPC)
For narrow distributions under typical operating conditions, number concentrations and mean mobility obtained with inversion algorithms are accurate to within 0.5% and 1.0%, respectively
Our analysis focuses on errors in the total number concentration, mean mobility, and standard deviation of the mobility distribution
Summary
An aerosol mobility size spectrometer system consists of an aerosol charger followed by Differential Mobility Analyzer (DMA) and an aerosol detector, usually a Condensation Particle Counter (CPC). Classifier voltage and will only be accurate for SMPS data in the limit of slow scan rates, i.e., where the ratio of the mean gas residence time in the classifier to the time constant for the exponential voltage scan ramp is smaller than about 0.02 In this limit, distortions of the transfer function due to changes in classifying voltage as particles travel through the classifier are negligible relative to other sources of error (Collins 2002; Dubey and Dhaniyala 2008; Mamakos et al 2008). Relatively low aerosol concentrations mandate slow scan rates or stepped voltage operation In such case, this analysis can provide accurate estimates of the biases resulting from use of the constant distribution approximation in the data analysis, as employed in the majority of SMPS systems. That Aerosol Research Letter describes a method to assess the performance of the mobility classifier and condensation particle counter in aerosol mobility size spectrometer systems
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