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Aerosol Type

How can I tell if the aerosols being observed are dust or smoke?

Currently there is no definitive test or product parameter available to conclude that the MODIS aerosol product is measuring dust or smoke.  Over ocean a low fine mode fraction is a strong indicator of dust but is not definitive.  Often ancillary information must be included to try to make this determination.  This ancillary information can include: AERONET data, AIRS dust product (over ocean), MISR data, OMI aerosol index, VIIRS suspended matter product, back trajectories which link to a dust or smoke origin.

What is aerosol fine mode fraction?

Atmospheric aerosols generally have a bimodal distribution.  The smaller particles are referred to as the fine mode or accumulation mode aerosols. These particles have radii between 0.1 and 0.25 microns. The larger particles comprise the coarse mode. These particles generally have radii between 1.0 and 2.5 microns.  The aerosol fine mode fraction is the proportion of fine mode aerosols to the total. This is an optical measurement of the proportion by volume.