Ozone
Environmental and health effects of ozone
Measurement of ozone
Ozone is an indicator of photochemical smog. Ozone is a colourless, highly reactive gas with a distinctive odour. It is formed naturally by electrical discharge (lightning) and in the upper atmosphere at altitudes of between 15 to 35km. Stratospheric ozone protects the Earth from harmful ultraviolet radiation from the sun.
However at ground level, elevated levels of ozone are produced
by photochemical reactions involving other air pollutants. Given sunlight and
suitable meteorological conditions, nitrogen oxides and volatile organic compounds
can react to form photochemical oxidants (also known as photochemical smog)
of which ozone is the principal component.
 |
The production of photochemical oxidants usually occurs over several hours which means that the highest concentrations of ozone normally occur on summer afternoons, in areas downwind of major sources of ozone precursors.
|
sunlight
|
sunlight
|
|||
| NO + VOCs |
>
|
NO2 + O2 |
>
|
NO + O3 |
Combustion processes (including motor vehicle engines, power stations, or bushfires) are major sources of nitrogen oxides and volatile organic compounds (VOCs) that react in sunlight to form photochemical oxidants.
Bushfires generate large quantities of the primary pollutants that form ozone, in addition to the everyday emissions from other sources. In recent years, ozone levels in south-east Queensland in excess of guideline values have almost always been associated with bushfires or burning-off events that occur during still weather conditions. The still conditions cause the emissions to build up near the source instead of being dispersed on winds.
Environmental and health effects
of ozone
At ground level, elevated ozone concentrations can cause health and environmental
problems. As well as affecting vegetation growth and damaging materials such
as rubber, fabric, masonry, and paint, it can also reduce visibility. Ozone
can affect the human cardiac and respiratory systems, irritating the eyes, nose,
throat, and lungs.
Ground-level ozone irritates the respiratory tract when present at concentrations
significantly above natural background levels. Symptoms of ozone exposure include
itchy and watery eyes, sore throats, swelling within the nasal passages and
nasal congestion. Effects from ozone are experienced only for the period of
exposure to elevated levels.
Air quality standards
The recommended air quality goals of 0.10 ppm (1-hour exposure period)
and 0.08 ppm (4-hour exposure period) have been derived to maintain ambient
concentrations below the levels at which effects are seen in sensitive members
of the population.
Measurement of ozone
Ozone exhibits strong absorption in the ultraviolet spectrum around 250nm
(nanometres). It is this very property by which the ozone layer protects the
Earth from the high energy UV radiation emitted from the sun and it is utilised
in the instruments that monitor ground-level ozone concentrations.
Ambient air is drawn through a flow cell which is irradiated with ultraviolet light of wavelength 254nm. The degree of UV light absorption compared with ozone-free air generated using a manganese dioxide scrubber, is a measure of the amount of ozone. Ozone is also measured using DOAS instrumentation.
 |
Last updated: 07 April 2006
