Combustion efficiency and emission factors for wildfire-season fires in mixed conifer forests of the northern Rocky Mountains, US Missoula Fire Sciences Laboratory, Rocky Mountain Research Station, United States Forest Service, Missoula, Montana, USA
30 Jul 2013
Received: 28 November 2012 – Published in Atmos. Chem. Phys. Discuss.: 03 January 2013 Abstract. In the US, wildfires and prescribed burning present significant challenges to
air regulatory agencies attempting to achieve and maintain compliance with
air quality regulations. Fire emission factors (EF) are essential input for
the emission models used to develop wildland fire emission inventories. Most
previous studies quantifying wildland fire EF of temperate ecosystems have
focused on emissions from prescribed burning conducted outside of the
wildfire season. Little information is available on EF for wildfires in
temperate forests of the conterminous US. The goal of this work is to
provide information on emissions from wildfire-season forest fires in the
northern Rocky Mountains, US.
In August 2011, we deployed airborne chemistry instruments and sampled
emissions over eight days from three wildfires and a prescribed fire that
occurred in mixed conifer forests of the northern Rocky Mountains. We
measured the combustion efficiency, quantified as the modified combustion
efficiency (MCE), and EF for CO2, CO, and CH4. Our study average
values for MCE, EFCO2, EFCO, and EFCH4 were 0.883,
1596 g kg−1, 135 g kg−1, 7.30 g kg−1, respectively.
Compared with previous field studies of prescribed fires in temperate
forests, the fires sampled in our study had significantly lower MCE and
EFCO2 and significantly higher EFCO and EFCH4.
The fires sampled in this study burned in areas reported to have moderate to
heavy components of standing dead trees and down dead wood due to insect
activity and previous fire, but fuel consumption data was not available.
However, an analysis of MCE and fuel consumption data from 18 prescribed
fires reported in the literature indicates that the availability of coarse
fuels and conditions favorable for the combustion of these fuels favors low
MCE fires. This analysis suggests that fuel composition was an important
factor contributing to the low MCE of the fires measured in this study.
This study only measured EF for CO2, CO, and CH4; however, we used
our study average MCE to provide rough estimates of wildfire-season EF for
PM2.5 and four non-methane organic compounds (NMOC) using MCE and EF
data reported in the literature. This analysis suggests the EFPM2.5 for
wildfires that occur in forests of the northern Rocky Mountains may be
significantly larger than those reported for temperate forests in the
literature and that used in a recent national emission inventory. If the MCE
of the fires sampled in this work are representative of the combustion
characteristics of wildfire-season fires in similar forest types across the
western US then the use of EF based on prescribed fires may result in an
underestimate of wildfire PM2.5 and NMOC emissions. Given the magnitude
of biomass consumed by western US wildfires, this may have important
implications for the forecasting and management of regional air quality.
Revised: 04 June 2013 – Accepted: 24 June 2013 – Published: 30 July 2013
Citation: Urbanski, S. P.: Combustion efficiency and emission factors for wildfire-season fires in mixed conifer forests of the northern Rocky Mountains, US, Atmos. Chem. Phys., 13, 7241-7262, doi:10.5194/acp-13-7241-2013, 2013.