Particulate matter are particles that are a airborne and can be inhaled which can cause health issues. The particles can be a mixture of solid and liquid droplets. The smaller the particles the deeper they can reach into the respiratory system and bloodstream. Most common source of PM is dust; the dust you see floating around in the sunlight is around 50 microns. Particles 2.5 microns and lower are considered the small particles that have trouble leaving the respiratory system. Air pollution, most commonly caused by combustion of solid and liquid fuels, produce particles of about 2.5 microns.
This is where sensors such as the SPS30 are implemented in HVAC and air quality applications. In the description and specifications of the datasheet you will see a PM with a number behind it. The number “x” in PMx stands for particle diameter smaller than “x” micrometers. PM2.5 defines inhalable particles with diameters that are generally 2.5 micrometers and smaller. PM10 defines inhalable particles with diameters that are generally 10 micrometers and smaller.