Simultaneous aerosol hygroscopicity and composition measurements were made usinga Hygroscopic Tandem Differential Mobility Analyzer(HTDMA)and a High Resolution Aerosol MassSpectrometer(HR-AMS)at the HKUST Supersite,located at a coastal suburban site in Hong Kong,in2011 and 2012.Two types of growth factor(GF)measurements were made by the HTDMA –(1)at afixed relative humidity(RH)at 90%and(2)over a range of RH between 10%and 93%.GF measurements at fixed 90%RH were made in May,September and November 2011 forambient aerosols at dry mobility diameters(Dm)of 75,100,150 and 200 nm.Throughout the study,bimodal GF distributions with a dominant more hygroscopic(MH)mode and a small fraction of thenon-hygroscopic or less hygroscopic mode(number fraction < 0.2)were observed.Overall,the averageensemble mean GF of maritime aerosols(1.53 – 1.59)was higher than that of continental aerosols(1.45 – 1.48).In the second half of Sept,the average MH mode GF(1.44 – 1.52)was significantlylower than that in other periods(1.53 – 1.64)due to the high organic loading under the influence of thecontinental airstream.GF prediction at 90%RH,based on the Extended Aerosol Inorganics Model witha constant GF of organic fraction(GForg)of 1.18,agree with 90%of measured data to within 10%.Another type of GF measurements was made fromJanuary to June and August 2012.A total of 58 cycles ofdehydration(decreasing RH)and hydration(increasingRH)were obtained for aerosols at Dm of 100 and 200 nmat RH between 10%and 93%.Kappa values(κ)of theMH mode during dehydration at different RHs werecalculated using the κ-equation derived in Petters andKreidenweis(2007).Overall,κ at 90%RH or above(κ >90)ranged between 0.16 and 0.49.The molar ratio(NH4-NO3)/SO4 was close to 2 in 51 cycles wherehysteresis was observed and 1.73 in the remaining cycleswhere no hysteresis was observed.Empirical equations topredict κ were developed using AMS mass fractionsincluding organic,sulfate and ammonium.Although theevaluation of κ as a function of RH showed that κ variesas RH decreases in the same dataset(图1),GF predictionbased on the equations developed showed agreement with13 additional measurements to within 10%.