There are seven types of criteria pollutants. These are gases and particles that are emitted into the atmosphere
and are harmful to human health. They include gases like nitrogen dioxide, ground level ozone, carbon
monoxide, lead and benzene, sulfur dioxide as well as particulate matter. These are the only pollutants with
national air quality standards (permissible amounts that may be emitted into the air).
Nitrogen Dioxide (NO2) falls into a group of highly reactive gases known as nitrogen
oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2
is emitted through the burning of various types of fuels. Sources include cars, trucks, buses, power
plants, and off-road equipment.
NO2 when at high concentrations in the atmosphere can cause irritation in the airways of
the respiratory system upon inhalation. Respiratory diseases such as asthma may become aggravated
causing symptoms such as coughing, wheezing or difficulty with breathing. These symptoms and side
effects could lead to increased hospital admissions and an increased susceptibility to respiratory
Lead and Benzene
There are many sources that release lead into the atmosphere, a major source being ore and metals
processing ( the lead concentrations are the highest around lead smelter) others include aircraft
that run on aviation fuel containing lead, waste furnaces and lead-acid battery manufacturers.
If lead is taken up by the body it begins to accumulate in the bones and can also cause severe damage
to the central and peripheral nervous systems. Other parts of the body that are affected are the
reproductive system, the kidneys and the heart. Lead exposure to infants and young toddlers has also
shown to decrease IQ levels as well as cause learning disabilities.
Benzene on the other hand is a volatile, organic compound which is emitted mostly from the petrol
chemical industry, vegetation fires and cigarette smoke. Benzene has shown to cause damage to the
immune, reproductive and central nervous systems. Long- term exposure to this chemical has also
proven to cause cancer.
CO is a colorless, odorless gas. Carbon monoxide can be fatal to humans in large quantities. The CO
molecules prevent the body from being able to take up as much oxygen from the air and can cause
strain to the heart or suffocation. CO is at its most dangerous in enclosed spaces (indoors). The
greatest sources of CO are cars, trucks and other vehicles or machinery that burn fossil fuels.
Household items such as gas burning stoves can also release CO.
There is in fact an entire group of sulfur oxides (SOx), all of which are toxic and
harmful to humans. SO2 occurs in the greatest concentrations. Another sulfur oxide
includes SO3 which is of less concern but the presence of which is usually determined by
that of its more significant counter part. SO2 is primarily emitted by sources of fossil
fuel combustion at power plants as well as in industrial processes. Sulfur dioxide is a colorless
gas that has an unpleasant odor and is one of the primary compounds which makes up acid rain,
consequently, it is also harmful to the environment. Exposure to SO2 can harm the human
respiratory system by making breathing difficult. Respiratory issues such as asthma are worsened by
the presence of sulfur oxides.
Ozone consists of three oxygen molecules. Depending on where it is found ozone can be both beneficial
or harmful. Beneficial ozone is found in the upper reaches of the atmosphere (the stratosphere) and
it is responsible for protecting us from harmful ultraviolet radiation from the sun. Harmful ozone
however is found at ground level (it is the main component of smog) where even in small
concentrations it can be harmful to human health.
Particulate matter (or PM) describes the mixture of solid particles and liquid droplets found in the
atmosphere. These particles include dust, dirt, soot, or smoke. These particles can be macroscopic
(visible with the human eye) or microscopic ( a microscope is needed to see them). Particulate
matter pollution is categorized by size, for example PM10 describes
particles with diameters that are 10 micrometers or smaller. PM2.5
however describes particles with diameters of 2.5 micrometers or smaller, these are extremely fine.
These pollutants can be detrimental to an individuals health as they make their way into the lungs
and bloodstream after being inhaled. Particulate matter pollution varies in size, shape and chemical
composition. The sources of these pollutants also vary significantly, some examples of such sources
include construction sites, unpaved roads, soil erosion of fields, smokestacks and wild fires. These
particulates also originate from complex chemical reactions in the atmosphere, the chemical
components of which are emitted by power stations, industries and vehicles.
Air Quality Monitoring
There are many different types of air quality control instruments that are used to measure the
concentrations of any given pollutant in the atmosphere. In South Africa there are currently 94 air
quality monitoring stations that have been set up by the National Ambient Air Quality Monitoring Network
(NAAQMN). These stations are monitored and operated by the South African government. There are many
non-governmental organisations that have their own stations as well. The data from these stations is
used to ensure that the concentrations of certain pollutants do not exceed legal and health limits.
These instruments are mainly used to measure pollutants such as carbon monoxide, sulphur dioxide, lead,
ozone, particulate matter and nitrogen dioxide.