How to calculate aerosol life time?

[qhan@uci_edu]

I would like to calculate the average atmospheric life time of dust particles deposited in each grid cell at certain time step. How should I do it? Can I solve this by knowing where the particles come from and what's is life time of the source grid? If so, which processes should be included? wet deposition, dry deposition, emission, how about the advection and diffusion?

Thanks,
Qin