(The modelling (by Ross et al.) was an old paper on the potential impact of suborbital launches using hybrid engines.)Black carbon produced by kerosene-fueled rockets such as SpaceX’s Falcon 9 and alumina particles produced by solid-fueled rockets lead to instantaneous radiative forcing. Modelling of the cumulative effect of emissions from 1000 annual launches of hydrocarbon-fuelled rockets found that, after one decade, the black carbon would result in radiative forcing comparable to that resulting from sub-sonic aviation. Although 1000 launches annually is 10 times the current rate, the construction and renewal of multiple mega-constellations will require dramatic increases in launches. Current launches likely cause non-negligible radiative forcing already
This 2018 Ross and Veda paper on rocket emissions seems to suggest that, basically, nobody knows what effect the launch industry has on the upper atmosphere because there isn't enough data. The main takeaway seems to be that alumina (produced by solid rockets but also by re-entering satellites) and black carbon (produced by kerosene rockets) aerosols cool the Earth's surface but heat up the stratosphere. Ozone depletion is apparently increased by this heating and by the surface area provided by the alumina, but the extent of the depletion is difficult to calculate[*]. Although a previous paper by Ross and Sheaffer claims that instantaneous(?) radiative forcing by BC and alumina are positive, the 2018 paper does note that the forcing is negative (although "negative" is missing from this sentence in the conclusion):
Rocket emissions, though they deplete ozone and cause climate forcing, so far have not been regulated..
Was the earlier finding wrong, or am I not understanding the significance of instantaneous radiative forcing?
The 2018 paper also says
Does this mean peroxides or weird upper atmosphere radicals?Methane fueled engines can be expected to emit, uniquely, potentially significant amounts of hydrogen oxides (HOx) into the stratosphere.
Don't get me wrong, the lack of data is troubling (a quick readup of ozone depletion indicates that ozone in the lower stratosphere is declining and we have no idea why) and the possible changes to atmospheric chemistry brought about by megaconstellations should be studied.
* and I can't read the sources.
P.S. Everyday astronaut does have a post on this subject, I found it after I wrote this.