The phrase "desert dust" refers to tiny particles of dirt, sand, or other substances that get carried by winds from deserts and spread to other areas. Full definition
As expected aerosol mass concentration was dominated by desert dust in coarse mode. (en.ilmatieteenlaitos.fi)
They can be natural, like desert dust, sea salt or pollen. (giss.nasa.gov)
This allows the researchers to use desert dust as an analogue for volcanic ash to test their system when they don't have a volcanic ash cloud to work with. (sciencenordic.com)