Impact of Anthropogenic Contaminants on Polar Ice Reflectivity and Heat Absorption: Soot and Carbon Nanotubes

Abstract

This thesis investigates the photothermal ice-melting effects of two anthropogenic carbonaceous contaminants; soot (black carbon) and carbon nanotubes (CNT) under controlled infrared radiation, examining how particle type, mass loading, deposition geometry, and ice structure govern the rate and spatial pattern of surface melting. The study focuses on ice samples prepared in custom 3D-printed containers under two structural configurations: crushed ice and solid ice which are subjected to surface, layered, and mixed-ratio contaminant deposition across a range of mass loadings from 5 mg to 1 g. The research adopts a systematic experimental approach, utilizing a four-thermocouple array embedded at defined heights within the ice column, a calibrated infrared radiation source, and high-frequency data acquisition at 240 Hz to resolve internal temperature profiles throughout each melting event. This detailed analysis reveals that photothermal heating is strictly surface-localized in all configurations: the highest thermocouple (TC4), positioned at the contaminant-ice interface, was the sole channel to register temperature rises driven by the surface deposit, while the lower thermocouples (TC1–TC3) remained thermally inert regardless of contaminant type, loading, or deposition method. Scanning electron microscopy characterization of both contaminants confirms their distinct morphologies; soot exhibiting spherical agglomerated nanoparticles and carbon nanotubes displaying high-aspect-ratio fibrous structures, which directly influence their optical absorptance and deposit packing behavior on the ice surface. Part of the study involves evaluating the non-monotonic relationship between contaminant mass and photothermal response, where both soot and carbon nanotubes exhibit complete suppression of surface heating at the intermediate 15 mg loading despite strong responses at 5 mg and 25 mg, and where mixed CNT-soot binary deposits at a fixed total mass of 25 mg produce a compositional window effect in which two specific ratios completely suppress melting acceleration while three others remain active. These findings highlight the complexity of particle-level interactions in co-deposited carbonaceous layers and the limitations of linear albedo-reduction models for predicting contaminant-driven melt dynamics. Furthermore, scaled-up experiments and solid ice trials demonstrate that ice structure and substrate thermal conductivity are as important as contaminant properties in determining melt acceleration, with the same gram-scale soot deposit producing a 33.6-minute swing in surface melted onset time between crushed and solid ice substrates. This study enhances the understanding of anthropogenic carbonaceous particle interactions with ice surfaces and underscores the need for geometry- and substrate-aware parameterizations of aerosol-driven albedo reduction in polar climate models.