The first difficulty that one must confront in any
definition of POM is to define the term “particulate”.
Usually it has an operational definition as any material
that does not pass through a given filter—usually a 0.5
μm filter. Glass fiber filters are widely used for the collection
and analysis of organic substances, but quite different
filter types have been used in different studies.
Thus, one needs to be aware that a “particle” collected
by a given filter may not be the same as a “particle” collected
by another. Material that passes through the filter
is termed “dissolved” (DOM), although in reality a broad
spectrum of particle sizes exists. Some material, such as
colloidal matter, does not fit neatly into either category.