from what i've looked up in five minutes (and knowing a bit of atmospheric chemistry) i'd guess the problem is chlorine and nitric oxide, not aluminum part. chlorine comes in as hydrogen chloride from ammonium perchlorate, and nitric oxide just appears when you heat up air enough, this means it also is generated during reentry and would also happen with oxygen/hydrogen rockets or any other for that matter. normally hydrogen chloride would be washed down, but when it's high enough this doesn't work. (there's also soot idk about this one)

there's alternative that does not introduce chlorine, and it's even a bit higher performance, but it's more expensive. (ammonium dinitramide) it's also more of matter of interest for military, because it leaves less smoke

slightly related: in 2019 there was discovered an illegal CFC manufacture in China, by way of CFC emissions being higher than expected. i think it was spotted remotely and only later traced to China. by 2021 it was shut down, and it's impressive because in CFCs, you're working with very friendly things like carbon tetrachloride, hydrogen fluoride, chlorine, antimony trifluoride and not at rt, but like, 70 atm 450C, not exactly something you can run in a bucket, everything is corrosive or at least would destroy your liver. in order for this to make sense they had to set up entire factory with capable chemical engineers, and they had to know they'll have customers that would violate Montreal protocol