https://en.wikipedia.org/wiki/Particulates
‘Atmospheric aerosol particles – also known as atmospheric particulate matter, particulate matter (PM), particulates, or suspended particulate matter (SPM) – are microscopic solid or liquid matter suspended in the atmosphere of Earth’
SPM is not always ‘microscopic’ in nature. The definition should include multiple size ranges as that is what industry has to monitor as part of their Environmental Compliance approval letters. It is very misleading…..I have had a few students question this statement after reading regulatory information.
Pamela's Blog 