Nucleation kinetics in drying sodium nitrate aerosols

TL;DR

This study develops a numerical model to analyze evaporation and nucleation in sodium nitrate aerosols, revealing differences in crystallization behavior compared to sodium chloride, with implications for understanding aerosol drying processes.

Contribution

Introduces a numerical model for aerosol droplet evaporation and nucleation, comparing sodium nitrate and chloride, and evaluates classical nucleation theory's applicability.

Findings

Sodium chloride droplets crystallize at all drying rates.

Sodium nitrate droplets can lose water without crystallizing.

Classical nucleation theory fits chloride but not nitrate droplets.

Abstract

A quantitative understanding of the evaporative drying kinetics and nucleation rates of aqueous based aerosol droplets is important for a wide range of applications, from atmospheric aerosols to industrial processes such as spray drying. Here, we introduce a numerical model for interpreting measurements of the evaporation rate and phase change of drying free droplets made using a single particle approach. We explore the evaporation of aqueous sodium chloride and sodium nitrate solution droplets. Although the chloride salt is observed to reproducibly crystallise at all drying rates, the nitrate salt solution can lose virtually all of its water content without crystallising. The latter phenomenon has implications for our understanding of the competition between the drying rate and nucleation kinetics in these two systems. The nucleation model is used in combination with the measurements of crystallisation events to infer nucleation rates at varying equilibrium state points, showing that classical nucleation theory provides a good description of the crystallisation of the chloride salt but not the nitrate salt solution droplets. The reasons for this difference are considered.