| Air pollution is caused by the emission of
gas, liquid vapour, or solid particulate matter into the atmosphere as a result of human
activity. Apart from the impact on the natural environment, air pollution can adversely
affect human health and well being. Sufficient increases in the concentrations of various
ambient air-pollutants can cause increased mortality, morbidity and deficits in pulmonary
function as well as cardiovascular and neurobehavioral effects. |
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| Contents of CONTEXTUAL INFO on Air
Quality: |
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| Air pollution and climatic inversion |
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| The CMA, like many other cities in the world, is faced with deteriorating
air quality. Increased air pollution coupled with adverse climatic conditions, result in a
decrease of ambient air quality in the CMA. The CMA experiences higher pollution levels
during March and September due to low level temperature inversions where pollutants are
trapped in a mass of stable air (CMC, 1998). The high concentrations of nitrogen oxides
(NOx) and hydrocarbons, during inversion conditions, and the high level of
solar activity during cloudless and wind free days, increases the probability of
photochemical smog episodes (CMC, 1998). In addition to health effects, smoke-related air pollutants contribute to
incidences of brown haze that extend over most of the CMA. This haze reduces visibility
and degrades the natural beauty of the metropole.
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| Air quality monitoring |
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| At present continuous air quality monitoring is carried out at 9 sites
throughout the CMA (see Map 1). Presently, the concentration levels of the following pollutants
are monitored: lead; sulphur dioxide; oxides of nitrogen, ozone and particulate matter
(PM10). Volatile organic compounds (VOC) have been monitored in specific surveys. Carbon
dioxide and monoxide are not yet monitored.
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| Figure 1,
2 and 3 show the concentration levels for
nitrogen dioxide, sulphur dioxide and ozone respectively. Figure 4
shows lead levels for the monitoring stations at Goodwood and City Hall. The variability
in annual means can be attributed to variations in climatic conditions, rather than any
improvement in controlling the source of the pollutant. Nitrogen dioxide levels are particularly high at City Hall in the
CBD and are primarily caused by vehicles. The levels of sulphur dioxide, a pollutant
emitted from industrial sources and diesel vehicles, show a decline in recent years. The
annual means of ground level ozone, which is formed by the reaction between nitrogen
oxides and volatile organic compounds (VOC) in the presence of sunlight (UV light), have
remained fairly constant between 1992 and 1997.
Lead levels have been relatively low since
the reduction of lead in petrol in 1989, however the levels at Goodwood show an upward
trend and those at City Hall are, on average, higher. |
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| Figure
1 |
| Nitrogen dioxide
levels at City Hall and Goodwood (source: CMC, 1998) |
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| Figure
2 |
| Sulphur dioxide
levels at City Hall and Goodwood (source: CMC, 1998) |
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| Figure
3 |
| Ozone levels at City
Hall and Goodwood (source: CMC, 1998) |
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| Figure
4 |
| Lead (Pb) levels at
City Hall and Goodwood (source: CMC, 1998) |
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| Figure 5, 6, 7, and 8 show the number of times the World
Health Organisation (WHO) guidelines were exceeded and the number of times that 50% of the
guideline was exceeded for nitrogen dioxide, sulphur dioxide and ozone. The number of
times that 50% of the guideline is exceeded is a good indication of trends, although not
an air quality standard. For nitrogen dioxide the CBD shows an upward trend from 1992,
dropping in 1996 while Goodwood is more variable (Figure 5 and 6). There have been few sulphur dioxide exceedances in recent years at
City Hall (Figure 5), however a few exceedances have been recorded
at the Table View site due to local industry sources (CMC, 1998). The number of days on
which 50% of the WHO guideline for ozone levels was exceeded has increased since 1992
(Figure 8). All
tables are extracted from the baseline study on air quality undertaken by Air Pollution
Control and Air Quality Monitoring Divisions of the CMC (CMC, 1998).
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| Exceedances
of the World Health Organisation Guideline for nitrogen dioxide (1988-1996) (source:
CMC, 1998) |
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| Exceedances
of the World Health Organisation Guideline for sulphur dioxide (SO2: 1988-1996)
and ozone (O3: 1992-1997) (source: CMC, 1998) |
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| Figure
9 |
Number
of days on which 50% of the United Kingdom Guideline for Particulate Matter less than 10
microns was exceeded
(source: CMC, 1998) |
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| The number of days on which 50% of the
United Kingdom (UK) guideline for particulate matter was exceeded is shown in Figure 9. This percentage is a good indicator of trends in pollution
levels. There has been an increase in the number of days that 50% of the UK guideline was
exceeded in 1996 and 1997 at Drill Hall and Goodwood. Particulate matter (PM10 and
PM2.5) pose a health risk as they can penetrate deep into the lungs. They also
have a negative effect on visibility over the CMA. PM2.5 has been shown to be
the larger contributor to brown haze which occurs over the CMA at certain times of the
year, with 47% resulting from diesel vehicles (ERI, 1997). Petrol vehicles and wood fires
also contribute significantly to these high levels. |
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| Table 1 provides the World Health Organisation
guidelines for levels of nitrogen dioxide, sulphur dioxide, ozone and lead, and the United
Kingdom guidelines for particulate matter concentrations. These provide a benchmark to
indicate unacceptably high levels of air pollution, which pose a threat to human health.
The current South African daily guideline for particulate matter is 180 µg/m3,
which is currently being revised, has never been exceeded at any monitoring station in the
CMA. Developed countries have adopted a daily guideline of 50 µg/m3, which is
exceeded at most monitoring sites in the CMA on 10 to 35 days per year. |
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Pollutant |
Guideline |
Organisation |
| Nitrogen Dioxide |
200 µg/m3
– hourly mean |
World Health
Organisation |
| Sulphur Dioxide |
125 µg/m3
– 24 hour mean |
World Health
Organisation |
| Ozone |
120 µg/m3
– 8 hour running mean |
World Health
Organisation |
| Lead |
0.5 µg/m3
– annual mean |
World Health
Organisation |
| Particulates (sub
10 microns) |
50 µg/m3
– 24 hour running mean |
United Kingdom |
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| In addition to the quantitative monitoring of air pollution levels, local
councils also monitor qualitative data in the form of complaints from the public with
respect to air pollution. In 1998, a total of 303 complaints, regarding various forms of
air pollution and ranging in severity, were registered throughout the CMA: 38 in
Blaauwberg; 109 in City of Cape Town; 49 in South Peninsula; 4 in Helderberg; 26 in
Oostenberg; and 77 in the City of Tygerberg.
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