Vertical Distribution of Atmospheric Ice Nucleating Particles in Winter over Northwest China Based on Aircraft Observations

The concentration of ice nucleating particles (INPs) in the cloud layer affects cloud processes more importantly than at the ground level. To make up for deficiencies in the observation of the vertical distribution of INPs over different background regions of China, airborne sampling of INPs was carried out at the altitudes of 2000-5500 m over Turpan, Xinjiang, northwest China on 29 December 2019, and the samples were analyzed in a static vacuum water vapor diffusion chamber. The sources and relationships of the INPs with meteorological conditions and the variation of the concentrations of aerosol particles of different sizes were explored. The results indicate that the concentration of INPs varies from 0.25 to 15.7 L-1 when the nucleation temperature changes from -17 to -26 degrees C and the relative humidity with respect to water (RHw) varies from 95 to 105%. The existence of an inversion layer near the planetary boundary layer (PBL) inhibits the vertical transport of aerosols, thus affecting the vertical distribution of INP concentration. INPs in the free atmosphere mainly originate from fine-mode aerosol particles transported from long distances by westerly winds and do not change significantly with height. The air mass in the PBL is short-range transported, and the INP concentration reaches 15.7 L-1 at T = -26 degrees C and RHw = 105%, which is obviously higher than that above the PBL. The analyses provide evidence that the meteorological conditions played an important part in regulating the vertical distribution of INPs.

Automated summary

The concentration of ice nucleating particles (INPs) in the cloud layer has a greater impact on cloud processes than at the ground level. Observations of the vertical distribution of INPs in different regions of China reveal the important role of meteorological conditions in regulating the vertical distribution of INPs. An inversion layer inhibits the vertical transport of aerosols, leading to variations in INP concentration at different heights. INPs in the free atmosphere primarily originate from fine-mode aerosol particles transported long distances by westerly winds and do not significantly change with height. Air masses in the planetary boundary layer (PBL) are short-range transported, resulting in higher INP concentrations compared to those above the PBL.