Department of Science, Information Technology and Innovation
What is ozone?
OZONE
Ozone (O3) is a colourless, highly reactive gas with a distinctive odour. It is formed naturally by electrical discharges (lightning),
and in the upper atmosphere at altitudes of 15 and 35km. It is this stratospheric ozone that protects the Earth from harmful
ultraviolet radiation emitted by the Sun.
At ground level, when meteorological conditions are right, elevated levels of ozone are produced by reactions involving
sunlight and other air pollutants, such as nitrogen oxides (NOX) and volatile organic compounds (VOCs). These reactions form
‘photochemical smog’ of which ozone is the principal component. Combustion processes, including motor vehicle engines,
power stations, and particularly bushfires, are major sources of nitrogen oxides and VOCs.
O3
The production of these photochemical oxidants usually occurs over several hours, which mean that the highest concentrations
of ozone normally occur on summer afternoons, in areas downwind of major sources of NOX and VOCs.
Sources of ozone
Why do we measure ozone?
At ground level, elevated ozone concentrations can cause health and
environmental problems. It can affect the human cardiac and respiratory
systems, irritating the eyes, nose, throat and lungs when present at
concentrations significantly above natural background levels. These effects
are only experienced during the exposure to elevated levels of ozone.
Ozone also affects vegetation growth, damages materials, such as rubber,
fabric, masonry and paint, and can reduce visibility.
30
Days >0.100 ppm (Air NEPM objective)
Days >0.080 ppm
25
Oxides of nitrogen
9%
63%
16%
4% 8%
motor vehicles
other mobile
industry
area based
biogenic
burning
Volatile organic
compounds
<1%
6%
22%
61%
6%
4%
1%
20
Volatile organic compounds (VOCs) react with oxides of nitrogen (NOX) to
produce ozone, the main component of smog. Emissions from the natural
processes of plant growth (biogenics) produce 61 per cent of VOC emissions in
South East Queensland.
Vehicles are the greatest man-made source of VOCs, which are created by
burning fuels in engines and evaporation. Vehicles are also the dominant source
of NOX, contributing 63 per cent of the total in South East Queensland.
15
10
5
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0
No discernible trend in ozone has been identified to date. However, with an
increase in urban growth and motor vehicle use the number of days with
high photochemical smog could become more frequent.
How is ozone measured?
Ozone exhibits strong absorption in the ultraviolet spectrum around 250nm
(nanometres). This property is the reason the ozone layer protects the Earth
from the high energy UV radiation emitted from the sun, and it is utilised in
instruments that monitor ground-level ozone concentrations.
To determine the ozone concentration, a sample of ambient air is drawn
through a reaction chamber, which is irradiated with ultraviolet light of
wavelength 254nm from a mercury vapour lamp. The intensity of ultraviolet
light detected by the instrument is reduced depending on how much the
ozone in the sample absorbs it.
A second sample, that has had all ozone removed using a manganese
dioxide (MnO2) scrubber, is then drawn through the reaction chamber,
resulting in a higher intensity of light reaching the detector. The difference
between the two values yields the concentration of ozone in the sample.
For more information about air quality in Queensland,
visit <http://www.qld.gov.au/environment/pollution/monitoring/air/>
or email: <[email protected]>
Air quality standards
The National Environment Protection Measure for Ambient Air Quality (Air
NEPM) standard of 0.10 ppm (one-hour exposure period) and 0.08ppm
(four-hour exposure period) have been derived to maintain ambient
concentrations below the levels at which effects are seen in sensitive
members of the population. In recent years, ozone levels in South East
Queensland above these goals have almost always been associated with
bushfires or controlled burning events during calm weather conditions that
generate large quantities of NOX and VOCs.