The radiative forcing of ozone produced from the 2004 fire complex in
Alaska and Yukon was estimated using the National Center for Atmospheric Research
(NCAR) Community Atmosphere Model (CAM 3) by comparing model simulations that
included fire emissions to a reference simulation where these emissions were turned off.
The total fire emissions for the 2004 fire season were optimized weekly to match
Measurements Of Pollution In The Troposphere (MOPITT) satellite observations of
column CO over northern North America (35). This yielded total emissions of 30 Tg CO
and a global annual mean O3 atmospheric perturbation for the first year of 0.9 Tg O3 –
although most of the ozone was concentrated in the northern part of the northern
hemisphere during summer. The burned area of the complex was approximately 4.45 x
S9
1010 m
2
. When normalized to the carbon emissions estimates we obtained for the
Donnelly Flats fire (1560 ± 610 g C m-2), this led to an adjusted radiative forcing from
ozone of 6 W per m2 of burned area, with an error estimate of 4 W m-2 that included
uncertainties in the emissions, the optimization (35), emission ratios (19), and the
radiative transfer calculations. Our approach for obtaining the adjusted radiative forcing
from the instantaneous forcing at the top of atmosphere (that was readily available from
CAM 3) is provided in more detail in section 1.11 and table S1.