We simulated black carbon (BC) and organic carbon (OC) aerosol direct radiative
forcing from the Donnelly Flats fire using CAM 3 (36). We used emissions described in
section 1.1, applying BC and OC emission factors from M. Andreae ((19), pers. comm.),
injected uniformly over the 8-day fire period. Aerosol optical properties were prescribed
(37). Aerosols were injected into the lowest atmospheric layer, and hydrophobic BC and
OC was transformed to hydrophilic components with an e-folding time of 1.2 days. We
estimate global shortwave (0.3-5.0 µm) instantaneous top of atmosphere (TOA) radiative
forcing from atmospheric BC and OC and surface forcing from BC in snow and ice with
an ensemble of two 10 year simulations (fig. S9). In each simulation, fire emissions were
injected into the model during June 11-18. Given that almost all of the instantaneous
radiative forcing from both atmospheric aerosols and their deposition on snow and sea ice
had dissipated after 6 months, this allowed for 10 independent model realizations within
each run.