Air Pollution Particulate Matter
1. What is Particulate Matter (PM)?
- 1.1 Why does particle size matter
- 1.2 How are particles formed?
- 1.3 Which materials are the main components of particulate matter?
Particulate matter is the
sum of all solid and liquid particles suspended in air many of
which are hazardous. This complex mixture includes both
inorganic particles, such
as dust, pollen, soot,
smoke, and liquid droplets. These particles vary greatly in
size, composition, and origin.
Particles in air are either:
- directly emitted, for instance when fuel is burnt and
when dust is carried by wind, or
- indirectly formed, when gaseous pollutants previously
emitted to air turn into
The same information on
1.1 Why does particle size matter
The aerodynamic properties
of particles determine how they are transported in air and how
they can be removed from it. These properties also govern how
far they get into the air passages of the
Additionally, they provide information on the chemical
composition and the sources of particles.
Particles have irregular shapes and their
aerodynamic behaviour is
expressed in terms of the diameter of an idealised sphere. The
sampling and description of particles is based on this
aerodynamic diameter, which
is usually simply referred to as ‘particle size’. Particles
having the same aerodynamic diameter may have different
dimensions and shapes. Some airborne particles are over 10,000
times bigger than others in terms of aerodynamic
Based on size,
particulate matter is often
divided into two main groups:
fraction contains the larger particles with a size ranging
from 2.5 to 10
fraction contains the smaller ones with a size up to 2.5
The particles in the
fine fraction which are
smaller than 0.1
Most of the total mass of airborne
particulate matter is
usually made up of
fine particles ranging from
0.1 to 2.5
Ultrafine particles often
contribute only a few percent to the total mass, though they are
the most numerous, representing over 90% of the number of
1.2 How are particles formed?
are produced by the mechanical break-up of larger solid
coarse fraction can include
dust from roads, agricultural processes, uncovered soil or
mining operations, as well as non-combustible materials released
when burning fossil fuels.
Pollen grains, mould spores, and plant and insect parts can also
contribute to the coarse fraction. Finally, evaporation of sea
spray can produce large particles near coasts.
are largely formed from gases.
Ultrafine particles (up to
are formed by nucleation,
which is the initial stage in which gas becomes a particle.
These particles can grow up to a size of 1
either through condensation, when additional gas condensates on
the particles, or through coagulation, when two or more
particles combine to form a larger particle. Particles produced
by the intermediate reactions of gases in the
atmosphere are called
fossil fuels such as coal,
oil, and petrol can produce
1.3 Which materials are the main components of particulate matter?
On average, the two main components of
particulate matter in
Europe are sulphate and
organic matter. This is
true both for fine particles
(PM2.5) and for
coarse and fine particles
However, near roads mineral dust is also a main component of
On days when the levels of
particulate matter in the
air are high
(PM10 exceeds 50
nitrate is also a major component of both
Soot, also referred to as
black carbon, makes up 5 to10% of
fine particles and somewhat
less of coarse particles;
near certain roads the proportion of soot can reach 15 to