Growth in numbers of motor
vehicles
Motor vehicles are the
main source of emissions of carbon monoxide, oxides of nitrogen
and organic compounds in the DMA. In addition, ground level
emissions from motor vehicles can have a greater local impact
than industrial emissions from chimney stacks. As motor vehicle
ownership, old and poorly maintained vehicles, and
the use of unleaded petrol without the use of catalytic
converters increases, the impacts on air quality
increases. The most significant impacts are likely to be
increased carbon monoxide concentrations, followed by
increases in nitrogen oxides and volatile organic compounds.
This will especially be the case near the higher density
traffic intersections and during peak traffic hours.
Industrial
development
Industrial processes are the main
source of anthropogenic particulate matter and sulphur
dioxide emissions in the DMA. They also emit significant levels of
oxides of nitrogen and organic compounds. When compared to the
United States and some countries in Europe, the coal and heavy
fuel oil burned by industry in the DMA has a high sulphur content.
This, combined with inefficient emission controls, has resulted in high sulphur
dioxide concentrations in heavily industrialised areas such as Durban South
Basin. As Durban's economy
grows, the pressure on air quality from industrial activity
will increase.
Influence of
climate
Local weather patterns and topography generally have a great influence
on air quality. In the DMA, pre -cold frontal weather systems
are often characterised by calm periods which can last
for several days, especially in winter. This
allows pollutants to accumulate with associated
decline in air quality. Strong winds have also been
found to cause "downdrafting" of pollutants towards the
ground.
During the winter months, there is
also a greater tendency for surface (temperature)
inversions at night which prevents
the dispersion of pollutants. A temperature inversion forms
when weather conditions trap a layer of dense air in an urban
basin or valley. In effect, a lid of warm air covers the
region and prevents the upward-flowing air currents (that
would disperse pollutants) from developing, and air
pollutants can build up to significant levels. At
sunrise, surface heating typically causes the inversion
'blanket' layer to dissipate and improves dispersion
conditions. Winter nights are also often characterised by land
breezes in the form of stable north westerly winds. In
conjunction with night time drainage winds down valleys, these
conditions do not favour pollutant dispersion and also result
in the carrying of pollution from inland regions towards the
coast.
