Origin of salt mixtures and mixed salts in atmospheric particulate matter

The atmospheric particulate matter contains components of natural and anthropogenic origin, some of them are sulphates and nitrates. Considering the usual occurrence of many ions in the atmosphere and the presence of water, the generation of salt mixtures and mixed salts is possible as a consequence of dissolution–precipitation processes within water droplets, e.g., in fog or haze. This contribution presents the Raman spectroscopic study of the sodium–potassium nitrate system, which generates a salt mixture of both compounds. A phase transition of a KNO3 crystal within a single solution droplet was observed. Additionally, we postulate the atmospheric generation of the mixed salt Na3(NO3)(SO4)H2O (darapskite) by dissolution–precipitation processes, because Na+, SO42–, and NO3 – can be usually found in the atmosphere. The polarized Raman spectra of synthetic darapskite are reported.