GAW Report No. 205 - IGAC Project

CHAPTER 2 - AFRICAvehicles, such as second hand engines from Europe (France-Aurevoir vehicles) and fromgeneralized 2-wheels individual transportation. The relative importance of traffic sources on NO 2 ,CO and VOC emissions is highlighted in Table 1 for Ouagadougou.Table 1 - Gas pollutants and their origin in Ouagadougou (in tons/year)PollutantsNO2 CO VOCEmission typeWood combustion 98 17.127 1.346Charcoal combustion 40 5.64 443Automobile 846 3.766 479Motorbikes 12 1.980 1.188Total 996 28.517 3.456Moreover, urban environment is degraded by external factors. For example, dust transportfrom northern deserts causes visibility reductions during Harmattan periods in late fall and winter(late November to mid-March). This pollution, reaching the surface in winter, is found aloft (900-1800 m) in summer. A second example as shown in Dakar [Doumbia et al., 2012], is generalizedbiomass burning that occurs during winter (dry season) [Liousse et al., 2010]. Finally, climaticfactors also play an important role: high temperatures and humidity in coastal cities, drought,winds, etc., cause conditions for intense photochemistry, which results in strong pollution formationenhancement.As a result, these cities and megacities are increasingly facing very acute public healthproblems due to air pollution at the origin of inhalation, ingestion and dermal contacts with pollutantgases and particles of all sizes (from nanometers to micrometers) and compositions.Seven representative capitals are selected in West Africa, Abidjan (Ivory Coast), Cotonou(Benin), Bamako (Mali), Dakar (Senegal), Ouagadougou (Burkina Faso), Lagos (Nigeria) andAccra (Ghana). For each of them, environmental features will be highlighted in terms ofgeographical location, population and other pertinent economical parameters. This will allow amore detailed examination of the impact of those parameters upon air quality in West African subregions.Ouagadougou in Burkina Faso (12° 22' 20" N, 1° 31' 15" W, 300 m a.s.l.) is the country's largestcity, with a population of 1.5 million inhabitants (2006). Ouagadougou, has a flat topography, withvery poor peripheral environment, and is regularly swept by harmattan winds. Based on theKöppen climate classification, this city features a typical tropical savanna climate. The city is in theSoudano-Sahelian area, with rainfall of about 900 mm per year. The rainy season stretches fromMay to October, with 30°C average temperature. The dry season runs from December to May witha minimum temperature (19°) in December-January and maximum temperature (45°) from Marchto May. Primary industries are food processing and textiles.Abidjan (5° 19' N, 4° 02'W) is the economical capital of Ivory Coast. It is the largest city of thecountry and the third-largest French-speaking city in the world, after Paris and Kinshasa. With apopulation of 8.9 million in 2006, Abidjan will soon become a megacity. The city has a tropicalmonsoon climate with a long rainy season from May to July, a short rainy season (September–November) and two dry seasons, though rain is observed even during these dry seasons. Abidjanis generally humid throughout the year, at levels generally higher than 80 percent. Total rainfall is31