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Seven trees are needed to absorb the carbon monoxide produced by one car. The equation is best explained when one knows that the average-sized tree absorbs one and half kilogrammes of CO2. On the other hand, driving your car for 50km per day produces almost 11.5 kilogrammes of CO2. The green belt's first phase (left) is one ambitious project that aims at reducing air pollution, especially around Greater Cairo. This aims at planting 500,000 trees to cover 100km around the capital, fed by treated water from sewage stations in various parts of the city. So far, almost 11,000 feddans have been planted in 16 governorates.