Abstract
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 1 Hz measurements of size distribution spanning a factor of ∼ 3 in particle diameter, which is sufficient to cover the entire range of growth factor (GF) for atmospheric aerosol particles at 90 % 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 2 %, the literature values for hygroscopic growth of NaCl particles. NaCl deliquescence was observed between 76 and 77 % RH in agreement with the theoretical value of 76.5 % (Ming and Russell, 2001), and efflorescence relative humidity (43 %) was found to lie within the RH range of 41 to 56 % 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 165 nm within less than 3 min, which makes it about 1 order of magnitude faster than traditional HTDMA systems.
Highlights
The hygroscopicity of atmospheric aerosols is a key parameter in determining their impact on global climate
Particles smaller than 150 nm often represent a large fraction of the cloud condensation nuclei population and may have a strong impact on human health (Chen et al, 2016). Using both laboratory and ambient measurements, we demonstrated that the humidity-controlled fast integrated mobility spectrometer (HFIMS) can provide growth factor measurements with 1 % precision for five representative particle diameters in less than 3 min – about 1 order of magnitude faster than traditional hygroscopicity tandem differential mobility analyzer (HTDMA) systems
The NaCl deliquescence transition observed by the HFIMS is just over 76 %, which is in agreement with the theoretical value of 76.5 % (Ming and Russell, 2001) and measurements by Hämeri et al (2001) and Cruz and Pandis (2000) of 76 and 75.6 %, respectively
Summary
The hygroscopicity of atmospheric aerosols is a key parameter in determining their impact on global climate. The abundance of hygroscopic particles that act as cloud condensation nuclei affects cloud formation and cloud droplet number concentrations, which in turn influences cloud albedo, coverage and lifetime (Twomey, 1977; Albrecht, 1989). These “indirect effects” of atmospheric aerosols on the Earth’s radiation balance remain one of the largest uncertainties in understanding climate change (IPCC, 2013). Most commonly particle hygroscopic growth is measured using hygroscopicity tandem differential mobility analyzer (HTDMA) systems, which consist of two differential mobility analyzers (DMAs) in series, separated by a means to control the sample flow relative humidity (RH).
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