Ice‐Nucleating Particle Concentrations and Sources in Rainwater Over the Third Pole, Tibetan Plateau

Abstract

The ice‐nucleating particles (INPs) modulate the microphysics and radiative properties of clouds. However, less is known concerning their abundance and sources in the most pristine and climatic sensitive regions, such as the Tibetan Plateau (TP). Here, to our best knowledge, we conduct the first investigation on INPs in rainwater collected in the TP region under mixed‐phase cloud conditions. The value of INP concentrations varies from 0.002 to 0.675 L−1 air over the temperature range from −7.1 to −27.5°C. This is within the INP spectra derived from precipitation under worldwide geophysical conditions and is also comparable with INP concentrations in the Arctic regions. The heat‐sensitive INPs account for 57% ± 30% of the observed INPs at −20°C and become increasingly important at higher temperatures, indicating biological particles as major contributors to INPs at temperatures above −20°C over the TP, especially on the day with additional input of biogenic materials carried by dust particles. Chemical analysis demonstrates that the rainwater components are mixture of dust particles, marine aerosol, and anthropogenic pollutants. Combined with the backward trajectory analysis, we show that dust particles transported from the surrounding deserts and originated from ground surface of TP may contribute to the heat‐resistant INPs at temperatures below −20°C.

Freezing Nucleus Spectra for Hailstone Samples in China From Droplet Freezing Experiments

“…This is likely because cloud‐level airborne INPs are largely activated to cloud droplets or ice crystals, and only a small fraction remains in the air (Gong et al., 2020; Pereira et al., 2021). The dominant species of immersion freezing INPs in cloud hydrometeor samples are similar to those in air samples, that is, generally biological aerosols at temperatures above −15°C (or above −20°C) and mineral dust particles at temperatures between −30 and −20°C (e.g., J. Chen et al., 2021; Christner et al., 2008; Hill et al., 2014; Joly et al., 2014; Joyce et al., 2019; Vepuri et al., 2021; Yadav et al., 2019; S. J. Zhang et al., 2020). The INP concentration in cloud hydrometeor samples can depend on the concentration of aerosols of certain species that dominate INPs and the scavenging efficiency of the aerosols into cloud droplets (Petters & Wright, 2015).…”