I don't think you'd need a drone. There are videos of drones (see "quadcopters) on YT that people have uploaded that are capable of reaching 30,000ft plus, but to the simple man the resources and knowledge of making those sort of craft are out of reach due to the programming and instrumentation of making such a craft. It'd be much easier to make a ground-based system of some sort that sucks in massive amounts of ambient air below the flight path of chem through some sort of filter that, after a fair amount of time of "filtering", the particulates caught in said filter could be sent off to a lab for analysis. An even easier way of analysis is to capture rainwater and send that off to an independent lab with some sort of spectrometer, who can test for each element ie Al, Ba, Sr.