Characterization of Emissions from Fires

All fires emit air pollutants in addition to nonpolluting combustion products; but fires vary widely in what pollutants are emitted in what proportion. Characterizing and managing air pollution from fires first requires knowledge of the amount and timing of what pollutants are emitted. Fires are a complex combustion source that involve several stages of combustion, several categories of fuels, and fire behavior that changes over time and with fuel and weather conditions; so the amount, rate, and nature of pollutants also vary widely. Characterizing emissions from fires requires explicit knowledge of fuel bed character and condition, combustion environment, and fire behavior. This section reviews the state of knowledge and predictive models necessary to characterize air pollutant emissions from prescribed and wildland fires.

All components of smoke from fires, with the exception of carbon dioxide and water, are generated from the inefficient combustion of biomass fuels. The amount of smoke produced is derived by determining the fuel consumed (tons per acre) in each combustion stage and knowing the size of the area burned, fuel characteristics, fire behavior, and combustion conditions (fuel moisture, weather parameters, and so forth). The fuel consumption is then multiplied by an emissions factor for each pollutant, which is an expression of the efficiency of combustion. An emission factor is the ratio of the mass of pollutant per unit mass of fuel consumed, and is a statistical average of measurements made in the plumes of fires containing differing fuel types and combustion stages. Errors and uncertainties arise in the estimates made during each step in the process of estimating emissions.  For more information see Emissions Inventories.