Smoke Emissions

Wildland fires release numerous chemical species, including greenhouse gases (e.g., carbon dioxide CO2), ozone (O3) precursors, and particulate matter (PM). Fine particles known as PM2.5 (particles < 2.5 μm in diameter) are the third largest source of emissions. In 2017, one week of extreme wildfire activity in northern California in the US produced as much as PM2.5 by road vehicles in the same state in an entire year (https://www.cnn.com/2017/10/13/health/california-fires-air-pollution-trnd, accessed 13 October 2017).

Carbonaceous material is a major component of PM2.5. It is comprised of black carbon (BC) and organic carbon (OC) which have distinct radiative properties. BC absorbs sunlight like a black body and heats the surrounding air. On the other hand, OC has scattering properties and reflects a part of incoming solar radiation back to space, causing cooling.

 

Smoke emission during the International Crown Fire Modeling Experiment (1997) in the Northwest Territories, Canada.
  

 

Calculation

The following presents a simple bottom-up approach to assess atmospheric emissions from wildland fires.

Formula

The amount (Q) of chemical species (X) emitted is determined by applying an emission factor to the estimates of area burned and fuel consumed:

Q(X) = A × B × EF(X)

with:

  • X = gas or particles;
  • A = area burned in hectares (ha);
  • B = fuel consumed in kilograms per square meter (kg/m²);
  • EF = emission factor in grams of chemical species X emitted per kilogram of dry matter burned (g/kgdm).

EF(X) is mostly dependent on the combustion mode. The two extreme cases generally considered are the flaming phase versus the smoldering phase.

Example

Consider a section of forest with the following characteristics:

  • An area burned of 100 hectares;
  • 60% and 40% of the fuel consumption occurred during the flaming and smoldering phases, respectively;
  • No unburned area is considered;
  • The total fuel consumed per unit area is 2.0 kg/m²;
  • Emission factors for PM2.5 are 14.0 g/kgdm and 22.9 g/kgdm for both phases, respectively.

The amount of PM2.5 emitted by the flaming phase is: 1,000,000 m² × 60% × 2.0 kg/m² × 14.0 g/kg = 16,800,000 g or 16.8 metric tons (or tonnes)

The amount of PM2.5 emitted by the smoldering phase is: 1,000,000 m² × 40% × 2.0 kg/m² × 22.9 g/kg = 18,320,000 g or 18.3 tonnes.

The total amount of PM2.5 emitted is then 35.1 tonnes.

 

Plume Rise

The buoyancy generated by wildland fires can propel gases and particles to high altitudes. Smoke plume rise depends on both fire behavior and atmospheric conditions at the surface and aloft. Fire behavior includes heat flux calculated from the area burned, fuel consumption and heat of combustion. Plume rise is a key parameter for the atmospheric transport of smoke plumes.

Smoke plume from the 2011 Slave Lake fire in Alberta, Canada
(Courtesy of Alberta Sustainable Resource Development).

Numerical modeling of the smoke plume released by
the 2011 Slave Lake fire in Alberta, Canada.

Smoke plume from the Slave Lake Fire as it reaches the first subdivision of the town on May 15, 2011 (video shot by a local resident).

Fire Behavior      Air Quality Impact

Last Modified 27 May 2023