What control the atmospheric lifetime of different metals in aerosols?
You could say that metals and aerosols reside in the atmosphere but I'm struggling to call that "atmospheric lifetime", which I've only heard in reference to gases.  The residence time of particulate matter is mostly a function of meteorology (e.g. PBL height, wind speed) and deposition (e.g. raining, settling velocity).  You've observed some metals that had a longer residence time.  I can think of two reasons for that:


Unique reactivity with other atmospheric components will change the mass and deposition velocity of particles.  Metals that do not react well in the atmosphere may not grow as quickly and therefore settle more slowly.
Specific metals may be used more prevalently in fireworks that obtain high altitude, such that the metal emissions are injected further up into the atmosphere and subjected to more atmospheric mixing and therefore longer settling times.


You might find this article by Licudine et al., (2012) of interest, which discusses monitoring of metals on New Years in Hawaii.