Abstract
The hygroscopic tandem differential mobility analyzer (HTDMA) has been frequently used to measure the hygroscopic properties of atmospheric aerosols at a fixed high relative humidity (RH) of about 90%. To evaluate if such measurements could be used to determine the hygroscopicity of aerosols at lower RH, simultaneous hygroscopic growth factor (GF) and size-resolved composition measurements were made with an HTDMA and a high-resolution aerosol mass spectrometer (HR-AMS), respectively, at a coastal site in Hong Kong from January to June and in August 2012. A total of 58 cycles of dehydration (decreasing RH) and hydration (increasing RH) of 100 nm and 200 nm particles with organic-to-inorganic mass ratio ranging from 0.19 to 1.97 were measured at RH = 10–93%. The Kappa (κ) equation developed by Petters and Kreidenweis in the year 2007 was used to determine (i) κ at individual RHs (κRH) and (ii) best-fit κ covering the range of RHs measured (κf) for the more-hygroscopic (MH) mode, which describes more than 80...
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