Scanning Mobility CCN Analysis—A Method for Fast Measurements of Size-Resolved CCN Distributions and Activation Kinetics

Abstract

We present Scanning Mobility CCN Analysis (SMCA) as a novel method for obtaining rapid measurements of size-resolved cloud condensation nuclei (CCN) distributions and activation kinetics. SMCA involves sampling the monodisperse outlet stream of a Differential Mobility Analyzer (DMA) operated in scanning voltage mode concurrently with CCN and condensation particle counters. By applying the same inversion algorithm as used for obtaining size distributions with a scanning mobility particle sizer (SMPS), CCN concentration and activated droplet size are obtained as a function of mobility size over the timescale of an SMPS scan (typically 60–120 s). Methods to account for multiple charging, particle non-sphericity, and limited counting statistics are presented. SMCA is demonstrated using commercial SMPS and CFSTGC instruments with the manufacturer-provided control software. The method is evaluated for activation of both laboratory aerosol and ambient aerosol obtained during the 2004 NEAQS-ITCT2k4 field campaign. It is shown that SMCA reproduces the results obtained with a DMA operating in voltage “stepping” mode.