Ice Nucleation Activity of Atmospheric Asian Dust Particles

Abstract

Airborne mineral dust triggers ice formation in clouds and alters cloud microphysical properties by acting as ice-nucleating particles (INPs), potentially influencing weather and climate at regional and global scales. Asian dust is an important source of atmospheric INPs. However, the ice nucleation activity (INA) of Asian dust, especially its sensitivity to particle size and anthropogenic pollution aging, remains poorly understood. In this study, we investigated the immersion mode ice nucleation properties and particle chemical characterizations of collected size-resolved Asian dust samples, covering eight particle size classes ranging from 0.18 to 10.0 μm. We also examined the chemical modification of aged dust particles via particle chemistry and morphology analyses. The measured total INP concentrations in the immersion mode ranged from 10-2 to 102 L-1 in dust events at temperatures between -25 and -5 ℃. An explicit size dependence of both INP concentration and surface ice active density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then levelled, due to the significant decrease in the number concentration of larger particles. The mass fraction of Ca2+ in element Ca and the mean relative mass proportions of supermicron Ca2+ increased by 67.0% and 3.5-11.2% in aged Asian dust particles, respectively, suggesting the occurrence of heterogeneous reactions. On the other hand, the total INP concentrations and total ice nucleation active site densities were consistent between aged and normal dust particles (0.62-1.18 times) without a statistically significant difference. And the INP concentrations and surface active site densities of chemically aged supermicron dust (1.0-10.0 μm) in each particle size class were nearly equal to or slightly higher than those of normal Asian dust, which were 0.70-2.45 times and 0.64-4.34 times at -18 ℃, respectively. These results reveal that anthropogenic pollution does not notably change the INP concentrations and does not impair the INA of Asian dust. Our work provides direct observational evidence and clarifies the non-suppression effect of anthropogenic pollution on the INA of East Asian dust, advancing the understanding of the ice nucleation of airborne aged mineral dust.