I might be misreading it, but that paper seems to bury a lot of the same assumptions that I’m objecting to. They assume a firestorm will form as part of the basis of how the fire is modeled, and then explicitly take the 5 Tg of stratospheric soot per 100 fires number and use that as the basis for further modeling.
For reference, here is what they say about their fire modelling:
The goal of the fire simulations in this work is to better characterize the spatial and temporal distribution of smoke from a mass urban fire resulting from a 15 kt nuclear detonation. Therefore, our modeling is informed by the Hiroshima firestorm, and the Hamburg firestorm, due to its rough similarity to the Hiroshima firestorm in size and duration. The assumption that all 100 detonations cause fires, and that these fires are more like the Hiroshima firestorm than Nagasaki, is a worst-case scenario. The studies of Penner et al. (1986) and Toon et al. (2007) also use fire parameters based on these historical cases (Hiroshima and Hamburg), so our fire parameters have the additional benefit of being similar to these previous studies. To produce simulations of fires similar to Hiroshima and Hamburg, it is assumed that the terrain is flat (i.e., topography does not provide shielding of thermal radiation) and there is uniform fuel loading over the area where thermal radiation is sufficient to ignite standard construction materials, such as wood. The WRF model source code is modified to allow for specification of surface fluxes of heat, water vapor and smoke (or black carbon), requiring quantification of these three fluxes, as well as the fire shape, size and duration.
The Hiroshima firestorm burned an area of about 11 to 13 km2 in 4 to 9 h, taking 20 to 30 min to develop into a firestorm (Glasstone, 1962; Rodden et al., 1965). The Hamburg firestorm burned a comparable 12 km2 in about 6 h (Carrier et al., 1985). Therefore, we specify a circular area with a 2 km radius (12.57 km2) for our fires. Each fire has a 30 min ramp-up period as surface fluxes increase linearly from zero, followed by a 4 h fire duration where surface fluxes are constant. The 4 h duration is chosen because it is the shortest time estimate for the fire in Hiroshima, and releasing a given mass of emissions and burning a given fuel amount over the shorter time period will result in higher smoke concentrations and heat fluxes, thus providing a worst-case estimate.
Thanks for the engagement, David and Bean!
For reference, here is what they say about their fire modelling: