Mineral dust aerosol is one of thelargest contributors to globalice nuclei, but physical and chemical processing of dust during atmospherictransport can alter its ice nucleation activity. In particular, severalrecent studies have noted that sulfuric and nitric acids inhibit heterogeneousice nucleation in the regime below liquid water saturation in aluminosilicateclay minerals. We have exposed kaolinite, KGa-1b and KGa-2, and montmorillonite,STx-1b and SWy-2, to aqueous sulfuric and nitric acid to determinethe physical and chemical changes that are responsible for the observeddeactivation. To characterize the changes to the samples upon acidtreatment, we use X-ray diffraction, transmission electron microscopy,and inductively coupled plasma–atomic emission spectroscopy.We find that the reaction of kaolinite and montmorillonite with aqueoussulfuric acid results in the formation of hydrated aluminum sulfate.In addition, sulfuric and nitric acids induce large structural changesin montmorillonite. We additionally report the supersaturation withrespect to ice required for the onset of ice nucleation for theseacid-treated species. On the basis of lattice spacing arguments, weexplain how the chemical and physical changes observed upon acid treatmentcould lead to the observed reduction in ice nucleation activity. [ABSTRACT FROM AUTHOR]