A3.2.6 Particulates


Particulates or Particulate Matter are often referred to as PM (again an abbreviation, not a chemical symbol). These are fine particles of solid or liquid suspended in a gas. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.

Naturally occurring particles include dust storms, forest and grassland fires, living vegetation and sea spray.

Man-made sources include road transport, homes, construction, mining and quarrying, industrial combustion plants and processes and public power generation. Particulate matter can also be formed by the transformation of gaseous emissions such as oxides of sulphur, nitrogen and VOCs.

Particulates are often referred to as Primary or Secondary. Primary Particles are those emitted directly to the atmosphere while Secondary Particulates are those formed by reactions involving other pollutants. In the urban context, most secondary particulate matter occurs as sulphates and nitrates formed in reactions involving SO2 and NOx.

Particles are also described by their size:

  • Coarse particulates have an aerodynamic diameter greater than 2.5 µm (micrometer or micron),
  • Fine particles have an aerodynamic diameter less than 2.5 µm.


In general, particles have irregular shapes with actual geometric diameters that are difficult to measure. Aerodynamic diameter is an expression of a particle’s aerodynamic behaviour as if it were a perfect sphere.

A lot of air monitoring activity focuses on PM10. This refers to particles with an aerodynamic diameter of 10 µm. These particles can settle in the bronchi and can cause respiratory illness. However, attention is now also being drawn to very fine particles (PM2.5 and PM1) as these can be carried deep into the lungs where they can cause inflammation and a worsening of the condition of people with heart and lung diseases.