The Role of Mineral Dust Aerosol Particles in Aviation Soot‐Cirrus Interactions

Abstract

Predicting cirrus cloud properties with confidence requires a sound understanding of the relative roles of homogeneous and heterogeneous ice formation. This study explores the effect of mineral dust and contrail‐processed aviation soot particles as ice‐nucleating particles (INPs) competing with liquid solution droplets in cirrus formation. We study aerosol‐cirrus interactions by accounting for atmospheric variability in updraft speeds and INP number concentrations. Our results confirm the dominant role of mineral dust in ice nucleation events in cirrus clouds. In addition, we show that pre‐existing thin cirrus may suppress ice formation when updraft speeds are low. We find that homogeneous freezing of liquid solution droplets dominates clear‐sky aerosol‐cirrus interaction above a threshold updraft speed determined by total number concentrations and ice nucleation abilities of INPs. When mineral dust particles exceed number concentrations of 10 L−1, they reduce homogeneously nucleated ice crystal numbers significantly and even prevent homogeneous freezing for frequently observed local updraft speeds between 10 and 20 cm s−1. When both mineral dust and aviation soot particles coexist with solution droplets, dust typically prevents ice nucleation by aviation soot. Aviation soot exerts a notable impact on cirrus ice numbers only if updrafts are weak, large soot particles are present in number concentrations that are considerably higher than typically observed in emission measurements, and/or number concentrations of mineral dust and other INPs are low. Overall, our results elucidate the role of aviation soot‐cirrus interactions in the presence of other INP types.

Ice Supersaturation Variability in Cirrus Clouds: Role of Vertical Wind Speeds and Deposition Coefficients

“…Homogeneous freezing of solution droplets appears to be frequently modified by more efficient ice‐nucleating particles (Froyd et al., 2022). ISSs are therefore to a large degree determined by local MTFs and competing ice nucleation (Kärcher, Marcolli, & Mahrt, 2023). However, our GW forcing model does not treat situations nearby deep convection or large topographic barriers.…”

Uncertainties in mitigating aviation non-CO2 emissions for climate and air quality using hydrocarbon fuels

“…In a follow-up study, the soot impact on cirrus was studied more realistically including competing effects of mineral dust particles (known to be efficient INPs), and variations in updras speeds and INP abundance. 109 The key points here are that the aerosol-cloud interaction of aviation soot in global climate modelling studies remains unresolved, and that the underlying emission, soot, is common to both contrail cirrus (an accepted signicant but uncertain positive net forcing) and aerosol-cloud interactions with cirrus. Until the latter forcing is better understood, any efforts to reduce soot emissions (with the prime purpose of reducing contrail cirrus forcing, either through operational means or changes in fuel), will, on current understanding, have a net uncertain climate outcome.…”

“…In a follow-up study, the soot impact on cirrus was studied more realistically including competing effects of mineral dust particles (known to be efficient INPs), and variations in updrafts speeds and INP abundance. 109…”