particle density = 2.5 g/cm3
deposition density = 1 g/cm3  (air gaps between grains, particles not compressed)
emission = 10^16 ug/hr        (original conversion factor used to get ug/m2 output) 

depth = density     deposition    m2->cm2      ug->g
       (1.0 cm3/g) (10^16 ug/m2) (m2/10^4cm2) (1g/10^6ug)

      = 10^6 cm