We have developed a new method to determine ice nucleating particle (INP)concentrations observed by the Texas A&M University continuous flow diffusionchamber (CFDC) under a wide range ofoperating conditions. In this study, we evaluate differences in particleoptical properties detected by the Cloud and Aerosol Spectrometer withPOLarization (CASPOL) to differentiate between ice crystals, droplets, andaerosols. The depolarization signal from the CASPOL instrument is used todetermine the occurrence of water droplet breakthrough (WDBT) conditions inthe CFDC. The standard procedure for determining INP concentration is tocount all particles that have grown beyond a nominal size cutoff as icecrystals. During WDBT this procedure overestimates INP concentration, because large droplets are miscounted asice crystals. Here we design a new analysis method based on depolarizationratio that can extend the range of operating conditions of the CFDC. Themethod agrees reasonably well with the traditional method under non-WDBTconditions with a mean percent error of ±32.1 %. Additionally, acomparison with the Colorado State University CFDC shows that the newanalysis method can be used reliably during WDBT conditions.
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