“…The intensity of the third peak at 2100-2200 cm −1 , attributed to the association mode of H-O-H, was much smaller (Ma et al, 2010a). It is possible but non-trivial to convert IR absorbance to the amount of adsorbed water, and the procedure used can be found elsewhere (Goodman et al, 2001;Ma et al, 2010a;Joshi et al, 2017;Ibrahim et al, 2018). It was found that the threeparameter BET equation (Joyner et al, 1945) could well describe water adsorption as a function of RH on mineral oxides (such as SiO 2 , TiO 2 , Al 2 O 3 , and MgO) (Goodman et al, 2001;Ma et al, 2010a;Joshi et al, 2017), authentic mineral dust from different sources (Joshi et al, 2017;Ibrahim et al, 2018) and Icelandic volcanic ash (Joshi et al, 2017).…”