Detonation Soot as an Ice Nucleating Particle (INP)
SETH THOMPSON, Sarah Brooks,
Texas A&M University Abstract Number: 125
Working Group: Aerosols, Clouds and Climate
AbstractTemperatures and pressures far exceeding typical atmospheric conditions arise from high explosive detonations, and by such means detonation soot forms with physiochemical properties unique from normal combustion. In nuclear war, high explosives within nuclear devices 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. 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 beyond -20°C in every detonation soot sample, aligning with oxidized combustion soot. Detonation soot with 137 μm diameter from air atmosphere detonations 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 with a rate coefficient increase of 1-2 orders of magnitude. Metal oxides may explain warm nucleation temperatures, and cuprous oxide was identified in 10% of detonation soot Raman spectra. 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 impact mineral dust deprived regions. Additionally, a fraction of the detonation soot population nucleated at temperatures as high as -9.2°C, comparable to mineral dust, which suggests the possibility of global impacts on ice cloud formation.