Fireworks - any sciencey people about?

[ChicagoBunfight]

Observing my neighbours fireworks party got me wondering. The fireworks don't get very high. If you could power them to go substantially higher no idea how much how would it affect the explosive power? If the atmosphere is thinner would the glittery bits spread out more, or would it have the opposite effect of a smaller more compact bang? Ta in advance.

At the heights a firework can reasonably reach the drop in air density will be pretty much negligible.

I agree with @safariboot - anything up to 10,000ft there's a negligible difference in air pressure. For the sake of argument, assuming you could get a firework up to 100,000 ft, then yes, the glittery bits would spread out more, but you'd need a telescope to see anything.