Smoke: The Invisible Wildfire Hazard
Wildfire smoke kills more people than flames. Fine particulate matter (PM₂.₅) from wildfire smoke penetrates deep into lungs, causing respiratory distress, cardiovascular events, and premature death. As wildfire seasons lengthen due to climate change, smoke exposure has become a major public health crisis affecting hundreds of millions of people annually, often far from the fire itself.
The Gaussian Plume
The Gaussian plume model, developed from decades of atmospheric dispersion research, provides the simplest physically meaningful estimate of downwind smoke concentration. The model assumes that turbulent mixing spreads the plume in a Gaussian bell curve pattern in both crosswind and vertical directions, with spreading rates determined by atmospheric stability. Despite its simplicity, it captures the essential physics: concentration decreases with distance, wind dilutes the plume, and stability controls the mixing rate.
Stability and Inversions
Atmospheric stability is the key control on smoke impacts. Unstable conditions (sunny afternoons) promote strong convective mixing that rapidly dilutes smoke but also brings elevated plumes to ground level. Stable conditions (clear nights, temperature inversions) trap smoke near the surface, creating hazardous concentrations that persist for hours. The worst smoke events occur when large fires burn during the day, lofting smoke that descends and accumulates during nocturnal inversions over populated valleys.
Plume Rise and Long-Range Transport
Intense wildfires generate their own convective columns, lofting smoke far above the surface. Plume rise depends on fire heat flux, wind speed, and atmospheric stability — large fires can inject smoke into the upper troposphere or even the stratosphere, where it enters long-range transport and affects air quality thousands of kilometers away. This simulation models the effective plume height after buoyant rise, connecting fire intensity to downwind ground-level concentration and public health impact zones.