Particulate matter with an aerodynamic diameter of less than 1.0 micrometres (µm) is referred to as PM1.0.
PM can be emitted directly from a source (primary PM) or formed through the interaction of other pollutants (secondary PM). The National Atmospheric Emissions Inventory estimates emissions of primary PM only.
There is no requirement to report emissions of these particle sizes under the NECR or UNECE Gothenburg Protocol, but emissions are estimated as a fraction of PM10 emissions. Combustion sources of particulates are generally more significant sources of these finer particle sizes than non-combustion sources.