Alexander Beadle is a science writer and editor for Technology Networks. Prior to this, he worked as a freelance science writer. Alexander holds an MChem in materials chemistry from the University of St Andrews, where he won a Chemistry Purdie Scholarship and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.
Air pollution is the contamination of air – either indoor or outdoor – by chemicals, particulates or biological agents that differ from the natural makeup of the atmosphere. Such pollutants can enter the air via natural means, such as volcanoes, but also as a direct result of human industrial activity.
Download this infographic to explore:
The different types of air pollutants
The sources of air pollution
How these different compounds can be monitored
AIR In this infographic, we explore the different
types of air pollutants and their sources,
as well as highlighting how these different
compounds can be monitored.
SOURCES OF AIR POLLUTION
Air pollution is the contamination of air – either indoor or
outdoor – by chemicals, particulates or biological agents
that differ from the natural makeup of the atmosphere.
Air pollutants can be categorized as primary or secondary
pollutants . Primary air pollutants are emitted directly
into the atmosphere, while secondary pollutants are
byproducts formed in the atmosphere as other gases or
primary pollutants undergo complex chemical reactions.
The World Health Organization (WHO) Global Air Quality
Guidelines establish air quality standards for five common
air pollutants, which have the strongest evidence to
suggest public health concerns.
Air pollutants can also be classified according to their origin (indoor or outdoor, natural or man-made) or
their physical properties, for example:
There are many other common air pollutants that are not formally included in the WHO air quality guidelines,
but that are often presented as contaminants of concern. These include:
Particulate matter includes coarse
particles (with a diameter between
2.5 μm and 10 μm), such as pollen,
wind-blown soil particles and dust
from industrial activities.
Finer particles (diameter less than
2.5 μm) such as the soot and
chemicals generated from the
burning of fuels are also included in
Carbon monoxide is a colorless, odor-less gas
produced by the incomplete combustion of wood
and fossil fuels. As an indoor air contaminant, carbon
monoxide is difficult to detect without specialized
equipment. Carbon monoxide can be potentially lethal
to humans if exposed for a long period of time.
Fixed in place
Long-term data collection for compliance monitoring,
Measurement availability for a wide variety of
Many natural environmental processes can generate
SURFACE DUST, SEA SALT, POLLEN AND SPORES
can all be considered natural sources for particulate
matter. Wind erosion can also introduce new particles
into the air.
VOLCANIC ERUPTIONS AND WILDFIRES can also
introduce soot particles, carbon dioxide and sulfur
dioxide into the atmosphere.
SWAMPS AND PEAT BOGS are natural sources of
the greenhouse gas methane, while lightning strikes
produce significant amounts of nitrogen oxides that
may go on to react with VOCs to form dangerous
In urban areas, most air pollution stems from human
activity, including industry and transport.
ROAD TRANSPORT is the dominant source of air
pollution in urban cities. Increased traffic and
congestion can also increase pollutant emissions.
THE COMBUSTION OF FOSSIL FUELS for transport
and in industrial processes is a major source of the
emission of carbon monoxide, hydrocarbons, nitrogen
oxides and VOCs into the atmosphere. This mixture
contributes towards the formation of more ground-level
ozone, which contributes to smog in industrial areas.
AIRBORNE MICROPLASTICS originating from the
breakdown of plastics and synthetic clothing can enter
the air and water vapor cycle, which carries the plastic
particles into even the most remote areas of the world.
OTHER INDUSTRIAL ACTIVITIES can produce more
specific environmental air pollutants; the agricultural
sector, through its use of fertilizers and rearing of animals,
is a major source for methane emissions and nitrogenbased
pollutants, such as ammonia and nitric oxide.
Sulfur dioxide is another harmful gas that is produced
mainly from fossil fuel combustion. Sulfur dioxide is the
most important acidifying compound responsible for
Portable, can be used in dense, urban environments
Near real-time air quality monitoring for specific
Ease of use supports community and citizen science
Volatile organic compounds (VOCs)
Nitrogen dioxide is a reddish-brown
gas produced predominately through
the burning of fossil fuels. It is one
of the most common indoor air
contaminants, due to heating systems
and cooking. It also plays a key role in
the formation of atmospheric ozone.
Ozone in the upper atmosphere
helps to protect the Earth from
the Sun’s harmful ultraviolet (UV)
rays. But ground-level ozone has
been linked to problems with lung
health. As climate change creates
favorable conditions for ozone
formation, combatting global
ozone production is expected to
be a strong focus for the coming
LEAD AND LEAD COMPOUNDS
RADIOACTIVE RADON GAS
ULTRAFINE PARTICLES BACTERIAL MOLD
SHORT-TERM EFFECTS LONG-TERM EFFECTS
IMPACTS OF AIR
The WHO estimates that almost the entirety of the world’s
population (99%) are breathing in air that exceeds ideal
WHO air quality limits. Regularly breathing in high levels of
air pollutants can be a danger to human health.
Air pollution, both indoor and outdoor, was responsible
for 6.9 million deaths in 2019. Long-term exposure to air
pollutants has also been linked to the development of
various cancers and issues with human and animal infertility.
The WHO now lists data collected in more than 6,000 cities
and settlements from 117 countries in their international air
Traditionally, air quality monitoring has been done at
fixed monitoring stations, often set up by governmental
departments. But the development of new sensing
technologies has also led to shifts in how air pollution is
Wheezing and coughing
Such low-cost, portable air pollution sensors can help support the more traditional monitoring stations
by allowing researchers and citizen science initiatives to contribute real-time, in-field measurements
for areas of interest – such as a city’s downtown during rush hour. Advances in wireless communication
infrastructure have also made it possible for data to be collected from widely dispersed networks of
small real-time sensors.
In addition to ground-based monitoring, satellite mapping data can also be used to monitor changes in
the concentration of carbon dioxide, methane, sulfur dioxide, nitrous oxides and other aerosols. Such
satellite instruments work by detecting tiny differences in the light reflected when sunlight strikes these
molecules and particles in the atmosphere.
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