Mass transfer effects in hygroscopic measurements of aerosol particles M. N. Chan1 and C. K. Chan2 1Environmental Engineering Program, School of Engineering, Hong Kong Univ. of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 2Department of Chemical Engineering, Hong Kong Univ. of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
Abstract. The tandem differential mobility analyzer (TDMA) has been widely utilized to
measure the hygroscopicity of laboratory-generated and atmospheric
submicrometer particles. An important concern in investigating the
hygroscopicity of the particles is if the particles have attained
equilibrium state in the measurements. We present a literature survey to
investigate the mass transfer effects in hygroscopicity measurements. In
most TDMA studies, a residence time in the order of seconds is used for
humidification (or dehumidification). NaCl and (NH4)2SO4
particles are usually used to verify the equilibrium measurements during
this residence time, which is presumed to be sufficient for other particles.
There have been observations that not all types of submicrometer particles,
including atmospheric particles, attain their equilibrium sizes within this
time scale. We recommend that experimentation with different residence times
be conducted and that the residence time should be explicitly stated in
future TDMA measurements. Mass transfer effects may also exist in the
measurements of other properties related to the water uptake of atmospheric
particles such as relative humidity dependent light scattering coefficients
and cloud condensation nuclei activity.
Citation: Chan, M. N. and Chan, C. K.: Mass transfer effects in hygroscopic measurements of aerosol particles, Atmos. Chem. Phys., 5, 2703-2712, doi:10.5194/acp-5-2703-2005, 2005.