Mass transfer effects in hygroscopic measurements of aerosol particles
- ISSN: 16807324
- DOI: 10.5194/acpd-5-4057-2005
The tandem differential mobility analyzer (TDMA) has been widely utilized to measure the hygroscop- icity of laboratory-generated and atmospheric submicrome- ter particles. An important concern in investigating the hy- groscopicity of the particles is if the particles have attained equilibrium state in the measurements. We present a litera- ture survey to investigate the mass transfer effects in hygro- scopicity measurements. InmostTDMA studies, a residence time in the order of seconds is used for humidification (or dehumidification). NaCl and (NH4)2SO4 particles are usu- ally 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 rec- ommend that experimentation with different residence times be conducted and that the residence time should be explic- itly stated in future TDMA measurements. Mass transfer ef- fects 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.