Abstract
Abstract. New analytical techniques are needed to improve our understanding of the intertwined physical and chemical processes that affect the composition of aerosol particles in the Earth's atmosphere, such as gas–particle partitioning and homogenous or heterogeneous chemistry, and their ultimate relation to air quality and climate. We describe a new laboratory setup that couples an electrodynamic balance (EDB) to a mass spectrometer (MS). The EDB stores a single laboratory-generated particle in an electric field under atmospheric conditions for an arbitrarily long length of time. The particle is then transferred via gas flow to an ionization region that vaporizes and ionizes the analyte molecules before MS measurement. We demonstrate the feasibility of the technique by tracking evaporation of polyethylene glycol molecules and finding agreement with a kinetic model. Fitting data to the kinetic model also allows determination of vapor pressures to within a factor of 2. This EDB–MS system can be used to study fundamental chemical and physical processes involving particles that are difficult to isolate and study with other techniques. The results of such measurements can be used to improve our understanding of atmospheric particles.
Highlights
Aerosol particles in the Earth’s atmosphere affect both the planet’s climate system and human health (Boucher et al, 2013; Lelieveld et al, 2015)
In this paper we demonstrate the ability of the coupled electrodynamic balance–mass spectrometer (EDB–MS) system to measure and quantify on a relative basis the constituent molecules of a multicomponent aerosol particle
From each spring point measurement, α and β × b were calculated using Eqs. (1) and (2), and the data were fit empirically to a second-order polynomial function. This polynomial function was used to convert β × b for each PEG particle, calculated via Eq (1), to α, which in turn was used to calculate a particle diameter via Eq (2). We found this method of determining particle diameters to provide values consistent with an alternate calculation method, in which α and β are related using the stability curves tabulated in Davis et al (1990), and b for this EDB is taken to be 2.8 × 10−3 (determined by optimizing the evaporation model fit to data for tetraethylene glycol (PEG-4) evaporation in the polyethylene glycol, average molecular weight 200 (PEG-200), evaporation experiment described below)
Summary
Aerosol particles in the Earth’s atmosphere affect both the planet’s climate system and human health (Boucher et al, 2013; Lelieveld et al, 2015) Because of these twin impacts, one long-standing goal of atmospheric research has been to assemble via experiment a detailed fundamental understanding of the coupled chemical–physical processes controlling the prevalence and composition of these particles, such as gas–particle partitioning (reviewed in Bilde et al, 2015), homogeneous and heterogeneous chemistry (e.g., George et al, 2015; Herrmann et al, 2015; Kroll et al, 2015), and kinetic barriers arising from high particle viscosity or phase separation (e.g., Bastelberger et al, 2017; Shiraiwa et al, 2013). A number of different properties have been studied in this way, including vapor pressures (Cai et al, 2015; Cotterell et al, 2014; Huisman et al, 2013; Krieger et al, 2017), hygroscopic growth (Cai et al, 2015; Cotterell et al, 2014; Rovelli et al, 2016), optical properties (Mason et al, 2015), liquid–liquid phase separation (Stewart et al, 2015), diffusivities and diffusion coefficients
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