SO₂ pollution. In urban areas around the CBD and higher income areas such as Sandton, Randburg, Melville and Southgate, lead from vehicle emissions and dust from mines (for the southern areas) cause pollution. In the inner city, SO₂ and O₃ levels are especially high in winter. In urban areas and the inner city, TSP (Total Suspended Particle) levels are also high due to exhaust emissions and re-suspended dust from vehicles. All pollution levels rise in the winter due to pollutants from vehicle emissions, coal fires, industries and mining areas being trapped close to the surface by temperature inversion layers. Circulation patterns over South Africa in the winter also do not disperse pollutants in a wavelike fashion as in summer.

A selected measurement of air pollution has been done in the former Johannesburg City Council area.

ANALYSIS OF AIR POLLUTION ACCORDING TO MAJOR SOURCES

• The worst affected area is around the Johannesburg CBD, which includes the industrial areas from Denver in the east to Industria North and Industria West in the west. These industries also lie mostly along the main rail and road commuter ways, which also experiences pollution from vehicle emissions. Traffic also converges in the CBD from the rest of Greater Johannesburg during the daytime. Morning and afternoon pollution levels along major roads coming into and leaving the CBD are consequently bad, with high primary (NO, CO and hydrocarbons) and secondary (ozone and NO₂) pollutant levels.

The Newtown monitoring station that covers the CBD shows an increase in average annual ozone levels from 0,012 to 0,013 ppm, as well as CO levels from 2,33 to 2,51 ppm during 1995/1996. A rise in ozone levels of 2-3 ppb per annum is estimated in the inner city. Carbon monoxide (CO) levels at Newtown is also much higher than at the other three monitoring stations, mainly due to vehicle emissions, and exceeds the national guideline during winter. Newtown further shows a decrease in NO_x, NO₂ and NO annual averages from 1995-1996 (GJMC Photochemical Smog Monitoring Program, 1996). Hourly averages of non-methane hydrocarbons at Newtown show an increase in winter. Levels rose from 0,4 ppm (which was below the national average hourly limit) in January 1999, to 7 ppm in February, then 21 ppm in March, 34 ppm in April, 46 ppm in May, 92 ppm in June and 54 ppm in July. This is due to the increase in coal fires, as well as seasonal circulation patterns and the temperature inversion level, which occur in autumn and winter.

Pollution in the CBD is further affected by wind blown dust from the mining belt, which increases TSP levels. Dust levels, measured as particulate matter (PM10 of size 10 um in ug/m³) exceeded the average daily guideline at Newtown once in February 1999, twice in April, 15 times in May, 10 times in June and 4 times in July 1999. This underlines the fact that winter circulation patterns in South Africa do not disperse pollutants due, in addition, to the role of inversion layers.

• To the south of the CBD through to Southgate, pollution comes mainly from the mining belt, as well as the large industrial areas such as City Deep, Booysens, Electron, Tulisa Park and Aeroton. The City Deep (industrial) monitoring station shows the second highest levels of CO after Newtown. Vehicle emissions and the burning of rubbish also affects this area. At the South Hills (suburban / residential) monitoring station, ozone levels are much higher than at the other stations, and exceeds the national average of 0,01 ppm during winter. This may be due to the fact that over 91% of the population here uses gas as a source of lighting, The burning of petroleum gas, as well as other fossil fuels increases primary and secondary (ozone) pollutants. The industries surrounding the area worsen the situation.

Annual average ozone levels decreased from 1984-1986 from 0,037 ppm to 0,016 ppm, then steadily increased to 0,033 ppm in 1990, and has since decreased and levelled out around 0,028 ppm. Annual average NO₂ levels at South Hills dropped from 0,1 ppm in 1984 to 0,02 ppm in 1985, and have since mainly fluctuated around this level. Annual average SO₂ levels have been fluctuating around 0,006 ppm.

• Air quality in the whole area surrounding Soweto is bad, where excessive amounts of coal is being burned. The worst affected areas are Diepkloof, northwest of Soweto, the whole area from Devland to Nancefield southeast of Soweto, where industries and informal settlements play a role, and the informal settlements from Klipspruit to Protea South. Use of energy rises here from June to September, and concentrations are only dissipated after the spring rains and when summer wind circulation patterns return. This explains why the national guideline for particulate matter (mostly smoke) is exceeded 20-30% of the time (in the winter months) in these coal-burning residential areas. Dust from untarred roads, refuse burning and bad odours from the Goudkoppies Landfill site, the Orlando Power station and informal industries also contribute to air pollution.

According to UNEP (1996) the coarse fraction of particulate matter (15>PM<2,5um) is the highest at lowest elevation sites and informal shanty areas in Soweto, where population densities are the highest and coal burning is excessive. Levels are the highest at Dhlamini, Jabavu and Chiawelo, which are at low to middle elevations, and low to middle socio-economic levels. Levels are the lowest at Diepkloof and Meadowlands to the north, which have a middle-high elevation and middle to high socio-economic status (Sithole et al, 1994, in UNEP, 1996). The particulate matter is derived from coal burning, dust, burning of garbage (lead, nickel, copper, zinc), vehicles (lead), biomass burning and secondary production of sulphates.

• In the formal residential areas of Lenasia and Ennerdale, and the informal settlements of Zakariyya Park, Vlakfontein, Elandsfontein and Lawley, pollution comes mainly from dust from untarred roads, rubbish and coal burning, and light industries. The worst affected areas are the informal settlements of Zakariyya Park, Thembelihle, Vlakfontein and Hospital Hill south of Lenasia, where excessive coal burning takes place. The Grasmere, Finetown and Weilers Farm areas east of Ennerdale, also burn excessive amounts of coal, and also lie next to the N1 and other major roads where vehicle emissions play a role. In the southern most part of the metropolitan area pollution is bad at the Poortjie settlement and to the east of Orange Farm. Excessive amounts of coal burning, vehicle emissions and dust from gravel roads and open land or agricultural activities are the causes.