Mass transfer effects in hygroscopic measurements of aerosol particles

[摘要] The tandem differential mobility analyzer (TDMA) has been widely utilized tomeasure the hygroscopicity of laboratory-generated and atmosphericsubmicrometer particles. An important concern in investigating thehygroscopicity of the particles is if the particles have attainedequilibrium state in the measurements. We present a literature survey toinvestigate the mass transfer effects in hygroscopicity measurements. Inmost TDMA studies, a residence time in the order of seconds is used forhumidification (or dehumidification). NaCl and (NH₄)₂SO₄particles are usually used to verify the equilibrium measurements duringthis 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 thistime scale. We recommend that experimentation with different residence timesbe conducted and that the residence time should be explicitly stated infuture TDMA measurements. Mass transfer effects may also exist in themeasurements of other properties related to the water uptake of atmosphericparticles such as relative humidity dependent light scattering coefficientsand cloud condensation nuclei activity.

[学科分类] 大气科学