Atmospheric aerosols have impacts on different scales from climate to human health.  Among different chemical and physical properties of aerosols, hygroscopic behavior plays a vital role when describing the impacts.  Characterization of atmospheric aerosols on their chemical compositions and physical properties by traditional approaches are limited by either the lack of comprehensiveness or low time-resolution.  Recent developments in aerosol instrumentation have provided tools for real-time characterization of atmospheric aerosols with sufficient comprehensiveness and time-resolution to capture the fast-changing characteristics of atmospheric aerosols.   

In August 2012, growth curve measurements of ambient aerosols at different relative humidity on ten days were made at the Hong Kong University of Science and Technology (HKUST) with the use of a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA), obtaining chemical composition and hygroscopic information of aerosols respectively.  After performing preliminary data analysis on hygroscopicity measurements, it was observed that hysteresis in the hygroscopic cycle exists.  Since hysteresis is not a commonly observed characteristic for ambient aerosols yet has significant impact on the characterization of water uptake thus direct effects on health and visibility reduction, correlations between the existence of hysteresis and aerosol chemical compositions will be explored to provide parameterization for the prediction of aerosols’ hygroscopic behaviors with a wide range of RH.  Additional measurements at the same site and by the same instruments will also be conducted to obtain another dataset for seasonal trend comparisons. The hypothesis from the preliminary results could therefore be confirmed with the new dataset.