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Buoyant plumes from various geophysical events significantly contribute to atmospheric pollution, affecting air quality, human health, and ecosystems. Understanding the dispersion dynamics of these plumes is essential for managing their environmental impacts and improving predictive models. Plume behavior is strongly influenced by the stability conditions of the atmospheric boundary layer, which vary between day and night due to diurnal changes in the Earth's surface temperature. During the daytime, solar heating creates an unstable boundary layer, often extending to several kilometers in height, while at night, radiative cooling leads to a stable boundary layer, typically a few hundred meters deep with weaker turbulence. Using large-eddy simulations, this study investigates how these diurnal variations in atmospheric stability affect the dynamics and dispersal behavior of turbulent plumes in crossflows. The results indicate that the plume's energy content and decay are highly influenced by the state of the atmospheric stratification, leading to distinctive patterns of dispersion, entrainment, and spread. By understanding the mechanisms governing the behavior of plumes, this study aims to contribute to better planning, management, and mitigation of their adverse effects. 

The transport and deposition of firebrand particles is an important fire spread mechanism in wildland fires. These particles can be transported by wind over large distances and can ignite secondary fires upon landing. The transport of firebrands by wind is a complex, multiscale process that is largely controlled by interactions between the firebrand particles and the atmospheric wind. To account for the complex temporal evolution of atmospheric turbulence over large scales, the use of large-eddy simulation (LES) techniques is necessary. However, filtering of subgrid-scale (SGS) turbulence in LES hinders the accuracy of particle transport models. In this work, we employ a Lagrangian SGS model in an LES framework to investigate the effects of small-scale turbulence on the transport of mass- and size-changing firebrand particles. The impact of SGS turbulence was analyzed by comparing landing and trajectory statistics for firebrand and regular (fixed size and mass) particles under different Stokes numbers. It was found that the presence of SGS turbulence modifies the particle transport behavior, which is characterized by smaller spanwise dispersions but larger travel distances along the streamwise direction compared with particles under no SGS turbulence. As expected, the enhanced velocity field produced by the SGS model has larger influence on the statistics of firebrand particles compared with regular particles due to the time-evolving reduction in particle mass and size induced by pyrolysis.