Particulate concentration associated with multiple burn units in complex terrain: A numerical study

Smoke from low-intensity prescribed fires jeopardizes the health and safety of both on-the-ground fire personnel and nearby communities, mainly through compromised air quality and reduced visibility. Accurate prediction of smoke dispersion is crucial to prevent unintended, potentially hazardous smoke intrusions into populated areas. This work addresses three specific knowledge gaps that limit smoke prediction accuracy: (i) the influence of complex terrain on smoke behavior, (ii) the effects of multiple active burn units, and (iii) the role of buoyant plume rise. A previously-validated Lagrangian particle dispersion model is employed to simulate particle dispersion in and around a river gap through an eastern Pennsylvania ridgeline. A series of idealized simulations is conducted in which particles are released within five 1-km x 1-km release zones, with fifteen combinations of release zones and release depths (chosen to roughly represent the impact of hypothetical fires of increasing intensity on buoyant plume rise and plume height). Results show that particle concentration magnitude and distribution downwind of the river gap are nonlinearly related to the number and location of release zones. Furthermore, the relative contribution from an individual source to downstream concentration may vary depending on whether buoyant plume rise is substantial enough to distribute particles throughout or above the mixed layer or is negligible with only near-surface distribution of particles. Overall, the results suggest that downstream smoke concentration magnitude and distribution are linked to both the spatial arrangement of sources and the plume characteristics, highlighting the need for consideration of these factors in smoke management strategies.