Chemical processing does not always impair heterogeneous ice nucleation of mineral dust particles

[1] Exposing Arizona Test Dust (ATD) particles to nitric acid vapor in an aerosol flow tube impaired subsequent deposition ice nucleation below water-saturation, but promoted condensation/immersion-freezing on approach to water saturation and had no apparent impact on freezing of activated droplets above water saturation. The fraction of particles capable of nucleating ice at −30°C was determined using a continuous flow diffusion chamber. Exposure to HNO₃ at 26% relative humidity with respect to water (RH_w) reduced the fraction of particles subsequently nucleating ice to below our quantification limit in the deposition nucleation regime below 97% RH_w, while leading to a sharper step-wise increase in ice nucleation between 97–100% RH_w compared to unreacted dust. These observations contrast with the effect of concentrated sulfuric acid condensation, which in most cases has been reported to reduce ice nucleation of ATD and other dusts both below and above water saturation.