Hi Matt
The air dispersion factor does not have anything to do with the the unit area emission flux rate Jw (g/m2/s)
The unit area emission flux rate is governed by equation 9.2 and takes into account fraction bare soil, but not size of site.
What the air dispersion factor is saying is that dust emitted at a constant rate per unit area from the entire site is diluted less on a bigger sites than it is on a smaller sites. Which entirely makes sense.
The bigger the number, the bigger the dilution, so the air dispersion factor decreases with site area.
The inverse of the air dispersion factor is used in Equation 9.1 to give the Particle Emission Factor PEF (m3/kg).
The inverse of the PEF (kg/m3) gives the concentration of PM10 soil dust in the air and is used in Equation 9.5 to calculate intake.
(the expression of PEF as m3/kg hides what it actually is (i.e. PM10 dust concentration kg/m3), but is a hangover from the original algorithms)
Hope this helps
Chris Dainton
Peak Environmental Solutions
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