A humidity-controlled fast integrated mobility spectrometer (HFIMS) for rapid measurements of particle hygroscopic growth

Abstract

We present a humidity-controlled fast integrated mobility spectrometer (HFIMS) for rapid particle hygroscopicity measurements. The HFIMS consists of a differential mobility analyzer (DMA), a relative humidity (RH) control unit and a water-based FIMS (WFIMS) coupled in series. The WFIMS (Pinterich et al., 2017) combines the fast integrated mobility spectrometer (Kulkarni and Wang, 2006a, b) with laminar flow water condensation methodologies (Hering and Stolzenburg, 2005; Spielman et al., 2017). Inside the WFIMS, particles of different electrical mobilities are spatially separated in an electric field, condensationally enlarged and imaged to provide 1ĝ€Hz measurements of size distribution spanning a factor of ĝ1/4 3 in particle diameter, which is sufficient to cover the entire range of growth factor (GF) for atmospheric aerosol particles at 90ĝ€% RH. By replacing the second DMA of a traditional hygroscopicity tandem DMA (HTDMA) system with the WFIMS, the HFIMS greatly increases the speed of particle growth factor measurement. The performance of the HFIMS was evaluated using NaCl particles with well-known hygroscopic growth behavior and further through measurements of ambient aerosols. Results show that the HFIMS can reproduce, within 2ĝ€%, the literature values for hygroscopic growth of NaCl particles. NaCl deliquescence was observed between 76 and 77ĝ€% RH in agreement with the theoretical value of 76.5ĝ€% (Ming and Russell, 2001), and efflorescence relative humidity (43ĝ€%) was found to lie within the RH range of 41 to 56ĝ€% reported in the literature. Ambient data indicate that the HFIMS can measure the hygroscopic growth of five standard dry particle sizes ranging from 35 to 165ĝ€nm within less than 3ĝ€min, which makes it about 1 order of magnitude faster than traditional HTDMA systems.