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

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 degrees 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 degrees C and become increasingly important at higher temperatures, indicating biological particles as major contributors to INPs at temperatures above -20 degrees 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 degrees C. Plain Language Summary Ice-nucleating particles (INPs) can catalyze the ice crystal formation through heterogeneous ice nucleation and thus play a profound role in the aerosol-cloud interaction. The Tibetan Plateau (TP) is one of the most vulnerable climate systems in the word, but we have very less knowledge on INPs over the TP, impeding our understanding of the aerosol-cloud interaction in this region. Here, the INP number concentrations and sources are quantified and identified over the TP under conditions relevant to mixed-phase clouds on a basis of comprehensive study on chemical composition and INP properties of rainwater. We show that biological particles are the dominant contributor of INPs at temperatures above -20 degrees C. The rainwater chemical components are mixtures of dust, marine aerosol, and anthropogenic pollutants. Dust particles may contribute to the heat-resistant INPs at temperatures below -20 degrees C.

Automated summary

This study investigates ice-nucleating particles (INPs) in rainwater collected in the Tibetan Plateau (TP) region under mixed-phase cloud conditions for the first time. It is found that biological particles are the major contributors to INPs at temperatures above -20 degrees C. The rainwater components consist of dust particles, marine aerosol, and anthropogenic pollutants, with dust particles potentially contributing to heat-resistant INPs at temperatures below -20 degrees C.