Heterogeneous nucleation of water vapor on different types of black carbon particles

Ari Laaksonen,Athanasios Nenes,Jussi Malila

doi:10.5194/acp-20-13579-2020

Abstract

Abstract. The heterogeneous nucleation of water vapor on insoluble particles affects cloud formation, precipitation, the hydrological cycle, and climate. Despite its importance, heterogeneous nucleation remains a poorly understood phenomenon that relies heavily on empirical information for its quantitative description. Here, we examine the heterogeneous nucleation of water vapor on different types of soots as well as cloud drop activation of different types of soots, including both pure black carbon particles and black carbon particles mixed with secondary organic matter. We show that the recently developed adsorption nucleation theory quantitatively predicts the nucleation of water and droplet formation upon particles of the various soot types. A surprising consequence of this new understanding is that, with sufficient adsorption site density, soot particles can activate into cloud droplets – even when completely lacking any soluble material.

Highlights

When water vapor becomes supersaturated – i.e., its relative humidity exceeds 100 % – it is in a metastable state and can form liquid water or ice
We demonstrate the new framework for different types of black carbon (BC) particles, which have long been known to be climate active – but with large uncertainty on their impact on direct radiative forcing and on their cloud formation ability and lifetime
We focus on the determination of water vapor adsorption parameters on graphite and on black carbon (BC) particles

Summary

Introduction

When water vapor becomes supersaturated – i.e., its relative humidity exceeds 100 % – it is in a metastable state and can form liquid water or ice. Despite its ubiquity and importance, the heterogeneous nucleation of water vapor remains poorly understood, even after more than a century of research (Pruppacher and Klett, 1997; Möller, 2008). This poor understanding is expressed by the lack of an established heterogeneous nucleation theory that provides quantitative comprehension of the process, and it translates into large uncertainty regarding the role of aerosol–cloud interactions in the climate system (Seinfeld et al, 2016). Molecular simulations (Lupi et al, 2014) are able to reveal aspects of heterogeneous nucleation phenomena, but they cannot provide a theoretical framework for describing heterogeneous nucleation in atmospheric and climate models on their own – and are impractical for implementation in models themselves

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