Air Pollution levels measured in Egypt exceed air quality limit values
The greater Cairo area also during the Autumn 1999 experienced several air pollution episodes with air pollution levels reaching very high concentrations due to a combination of emission from a number of different sources and adverse weather conditions.
The air pollution problem in Egypt
The main air pollution problem in Egypt is the level of suspended particles. Particles in ambient air are measured as.
- Total suspended particles (TSP),
- Particles less than 10 micrometer in diameter (PM10),
- Black smoke (BS, soot) and
- Dust fall.
The measured concentrations often ranged from 6 to 8 times the Air Quality Limit value (A.Q.L) as given by Environmental Law no. 4 for Egypt. It should be noted that the natural background level of dust in the atmosphere over Egypt is very high, probably higher than the Air Quality Limit level, due to the dry climate, windy conditions with re-suspended dust and large surrounding dessert areas.
SO2 concentrations may also exceed AQL levels in urban areas and close to industrial sources. The levels of NO2 seldom exceeded the AQL levels, even if traffic is one of the main sources for pollution in urban areas. This can be seen in the exceedances of CO limit values in the streets.
Very high concentration of PM10
Dry climate, dessert areas and windy conditions normally generate the larger particles found as TSP or as dust fall. The particles that are causing more health impact to people are the smaller particles. Our measurement show, for instance from data collected at Tabbin in southern Cairo, that the inhalable (thoracic) particles (diameter less than 10 micrometer, PM10) are mainly generated from industrial processes, and may thus also be carriers for other hazardous pollutants. (Sivertsen et.al. 1999). High concentrations of PM10 are also generated by traffic, especially diesel buses, in the streets.
PM10 are collected and analysed in different ways in the EIMP programme. The main differences are the continuous records of PM10 analysed every half-hour by beta attenuation, the sampling of PM10 on filters for gravimetric analyses and the filter analyses of black smoke (soot) by reflectrometric methods.
In Law no. 4 for the Environment of Egypt the only Air Quality Limit value given for PM10 is based on 24-hour average concentrations. The concentration level should not exceed 70 (mg/m3)
To illustrate the PM10 problem in the city centre of Cairo, PM10 and SO2 concentrations are shown as 24 hour average concentrations in the Figure below.
During some periods recorded both in September, October and November the PM10 concentrations were more than 5 times the air quality limit value. During some of these cases also SO2 concentrations exceeded the air quality limit values.
High concentrations of sulphur in some areas
The highest concentrations of SO2, which is an indicator for sulphur emissions from burning of fossil fuels and from industrial processes, were recorded in central parts of Cairo and at some industrial sites in the Delta and in Upper Egypt. The SO2 concentrations in Alexandria were lower than in Cairo, and did never reach the Limit values.
The NO2 concentrations
are about the same in Cairo and in Alexandria. These levels very seldom reach the Air Quality Limit levels.
Air Pollution episodes in Cairo
Air pollution episodes have been recorded in Cairo, as a result of specific meteorological conditions combined with air pollution created by several ground-based sources. Millions of people experienced very high levels of pollutants during these episodes. The main sources were traffic, open-air waste burning and a large number of small enterprises releasing air pollutants near the surface. Low wind speed conditions combined with stable atmospheric conditions created the problem. High concentrations of SO2 and PM10 were recorded on 20 September 1999. Instruments at Quolaly, FumAlKhalig and Maadi all recorded high pollution levels at the same time. “Episodes” can be seen in the Cairo atmosphere on 19-23 October and from 27 Oct to 2 Nov 1999. (see the Figure below)
Meteorology and smog
The main reason for the smog like episode experienced by a large part of the Cairo population, was adverse weather conditions with low and variable winds, high humidity and a strong temperature inversion at a few hundred metres above the surface. The emissions of air pollutants released from a number of different sources near the surface in the Cairo area added to a slowly transport of particles emitted from burning in the Delta.
A high-pressure area was situated north of Egypt with its centre in the Eastern Mediterranean, giving rise to a slowly movement of humid air from the north-east across the Delta into the Cairo area. Subsidence of air in the high pressure caused the formation of a temperature inversion in the lower atmosphere, which created a “lid” on the Cairo air mass. Under this lid the wind speeds were decreasing during the afternoon of 23 October to near calm conditions. At the end the local surface winds were turning to slowly move air pollutants back into Cairo from the south in the evening. The unusual high humidity together with high concentrations of suspended dust and other pollutants created what in Europe is called a “winter type smog episode”.