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Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles.

Physical chemistry chemical physics : PCCP (2018-12-20)
Matus E Diveky, Sandra Roy, Johannes W Cremer, Grégory David, Ruth Signorell
ABSTRACT

Photoacoustic spectroscopy is widely used to measure the light absorption of aerosols. However, the impact of key factors such as the effect of relative humidity and mass exchange on photoacoustic measurements are still poorly understood. We assess such measurement biases and their physical origin by analysing the photoacoustic signal of single tetraethylene glycol (TEG) particles at varying relative humidities. Our results show a decrease in the photoacoustic signal at elevated relative humidities for small particles (0.8-1.5 μm), while for larger sizes (2.2-3.2 μm) the trend is reversed. We model the photoacoustic signal to interpret the observed behaviour in terms of mass and heat flux contribution. The single particle photoacoustic signal analysis presented in this paper additionally allows for the retrieval of the mass accommodation coefficient. Fitting our experimental data to the theoretical model reveals values of αM ≈ 0.02-0.005 for water on TEG in the temperature range 295-309 K.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tetraethylene glycol, 99%