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Detonation Soot as an Ice Nucleating Particle
Abstract
Temperatures and pressures far exceeding typical atmospheric conditions arise from high explosive detonations, and consequently detonation soot forms with physiochemical properties unique from soot particles formed by combustion. In nuclear war, high explosive detonations produce and loft detonation soot into the upper troposphere and stratosphere where it has potential to be an ice nucleating particle (INP). Due to the importance of INPs in ice cloud formation and subsequent climate impact, it is critical to investigate the ice nucleating ability of all possible aerosol, including
unconventional aerosol like detonation soot. In this study, samples of detonation soot from two high explosives, PBX 9502 and Composition B-3, were analyzed from both air and argon atmospheres. Contact and immersion mode nucleation temperatures were determined through a series of freezing experiments using 137 and 225 μm particles. Detonation soot samples nucleated ice on average at temperatures warmer than commercially available nanodiamond, which freezes at -20.7°C. A rapid 2-3 orders of magnitude increase in ice nucleation rate coefficients was observed below -20°C in every
detonation soot sample, aligning with the nucleation rate coefficients of oxidized combustion soot. Size-selected 137 μm soot generated from denotation in an air atmosphere produce bimodal freezing distributions with primary and secondary nucleation modes centered at -20 and -13°C, respectively. The warm secondary nucleation mode enables more efficient freezing above -17°C with a rate coefficient 1-2 orders of magnitude faster than samples with only a primary mode. The presence of metal oxides within the samples may explain warm nucleation temperatures. Specifically, cuprous
oxide was identified in 10% of detonation soot Raman spectra. As our measurements show, commercially available cuprous oxide froze on average at -21.1°C. A nuclear exchange, producing 180 Tg of soot, would substantially increase global INP populations. Primarily, detonation soot would alter the concentration of INP in mineral dust deprived regions. Since a fraction of the detonation soot population nucleated at temperatures as high as -9.2°C, comparable to mineral dust, detonation soot may impact ice formation on a global level.
Citation
Thompson, Seth A (2022). Detonation Soot as an Ice Nucleating Particle. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /197782.