“…Understanding the factors controlling the change in extinction or scattering as a function of RH, known as f (RH), is important for evaluating remote sensing measurements (e.g., Brock et al, 2016;Crumeyrolle et al, 2014;Esteve et al, 2012;Ferrare et al, 1998;Hegg et al, 1993;Kotchenruther et al, 1999;van Donkelaar et al, 2015;Voss et al, 2001;Zieger et al, 2011Zieger et al, , 2012Ziemba et al, 2012), aerosol direct radiative forcing calculations (e.g., Attwood et al, 2014;IPCC, 2013;Kahn, 2011;Koloutsou-Vakakis et al, 1998;Nemesure et al, 1995), and atmospheric visibility estimates (e.g., Charlson et al, 1967;Malm et al, 2000). In general, particles composed primarily of organic material and dust are less hygroscopic Petters and Kreidenweis, 2007;Zieger et al, 2015), while those that are predominantly inorganic take up water more readily (e.g., Petters and Kreidenweis, 2007;Quinn et al, 2005). Particles may exhibit sharp phase transitions as they deliquesce, as well as hysteresis as they effloresce, especially for inorganic compositions (e.g., Santarpia et al, 2005;Tang, 1996;Zieger et al, 2014).…”