title: Vacuum FTIR Observation on the Dynamic Hygroscopicity of Aerosols under Pulsed Relative Humidity.
abstract: A novel approach based on a combination of a pulse RH controlling system and a rapid scan vacuum FTIR spectrometer (PRHCS-RSVFTIR) was utilized to investigate dynamic hygroscopicity of two atmospheric aerosols: ammonium sulfate ((NH4)2SO4) and magnesium sulfate (MgSO4). In this approach, rapid-scan infrared spectra of water vapor and aerosols were obtained to determine relative humidity (RH) in sample cell and hygroscopic property of aerosols with a subsecond time resolution. Heterogeneous nucleation rates of (NH4)2SO4 were, for the first time, measured under low RH conditions (<35% RH). In addition, studies of MgSO4 aerosols revealed that water mass transport may be limited by different processes depending on RH values (surface limited at 40% < RH < 52% and bulk phase limited at RH < 40%). Furthermore, we are also the first to report water diffusion constants in micron size MgSO4 aerosols at very low RH values. Our results have shown that the PRHCS-RSVFTIR is well-suited for determination of hygroscopicity of atmospheric aerosols and water transport and nucleation kinetics of liquid aerosols.
authors.affiliation: †Institute of Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China.|‡Department of Chemistry, University of Colorado Denver, Denver, Colorado 80217, United States.
authors.forename: Chun-Bo
authors.initials: CB
authors.lastname: Leng
authors.affiliation: †Institute of Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Shu-Feng
authors.initials: SF
authors.lastname: Pang
authors.affiliation: †Institute of Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: †Institute of Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Chen
authors.initials: C
authors.lastname: Cai
authors.affiliation: ‡Department of Chemistry, University of Colorado Denver, Denver, Colorado 80217, United States.
authors.forename: Yong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: †Institute of Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Yun-Hong
authors.initials: YH
authors.lastname: Zhang
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000645:Ammonium Sulfate / Q000737:chemistry; D004058:Diffusion; D006813:Humidity; D007700:Kinetics; D008278:Magnesium Sulfate / Q000737:chemistry; D015203:Reproducibility of Results; D017550:Spectroscopy, Fourier Transform Infrared; D014618:Vacuum; D014867:Water / Q000737:chemistry; D017155:Wettability
chemical_list: D000336:Aerosols; D014867:Water; D008278:Magnesium Sulfate; D000645:Ammonium Sulfate