What are particles?
Particles or particulate matter (PM) are tiny bits of solids or liquids suspended in the air.
They are a complex group of pollutants that vary in size, shape, composition and origin.
These properties can also vary from place to place and time to time.
Particles originating from road traffic include carbon emissions from engines, small bits
of metal and rubber from engine wear and braking as well as dust from road surfaces. Others
include material from building and industry as well as wind-blown dust, sea salt,
pollens and soil particles.
People often associate particles with smoky engines, but the majority of particles that
can penetrate the airway are too small to see, and thus can be present in air that seems
Larger particles are generally filtered in the nose and throat and do not cause problems.
Particles smaller than about 10 micrometers, referred to as PM10 and particles smaller that 2.5 micrometres (PM2.5), can settle in the
airway and deep in the lungs and cause health problems.
The health effects of particle air pollution have been widely studied, and include premature
death and the worsening of heart and lung disease, often increasing admissions