Chapter 2: State and Trends
atmosphere and human activities, partly because human activities release pollutants to the atmosphere in amounts that are comparable to, or even exceed, the natural rates of mobilization (Crutzen and Andreae 1990). Tamatamah et al. (2005) estimated that 13.5 tonnes of phosphorus were deposited annually into Lake Victoria from the atmosphere, representing 55 per cent of the total phosphorus input to the lake. In Ghana, Breuning-Madsen et al 2015 noted that the Harmattan dust contributed an average 10 per cent of calcium, magnesium and potassium, and 20–40 per cent of phosphorus from natural sources to agro-ecosystems.
2.1.3 Transboundary emissions and atmospheric deposition
Much of the deposition of air pollutants across the continent is attributable to transboundary sources. This is particularly the case with large suspended particulate matter such as dust. The Sahara Desert is the main global source of dust. About 12 per cent of Saharan dust moves northwards to the Mediterranean Sea and Europe; 28 per cent westwards crossing the Atlantic Ocean to the USA, the Caribbean, and South America; and 60 per cent southwards to the Gulf of Guinea (Engelstaedter et al. 2006).
In West Africa, atmospheric dust, which is composed of Saharan particles and is transported by Harmattan wind, is a significant seasonal climatic event. Continental aerosols are transported by the Harmattan winds from northeast Senegal (Doumbia et al. 2012). The dust affects the chemical quality of rainfall, which typically is alkaline and strongly mineralized. Orange et al. (1993) indicated the existence of an African chemical signature of the atmospheric fluxes, which contributes a suite of chemicals ranging in mass from 1 300 kg per hectare per year in the Sahel zone to 365 kilogrammes per hectare per year in the Guinean zone.
Ozone emissions across Africa’s troposphere are mainly from anthropogenic sources. For example, Aghedo et al. (2007) found an increase of surface ozone concentration of about 2–7 parts per billion by volume (ppbv) in West Africa due to anthropogenic emissions during the boreal summer,
from 1990 to 2010 were consistently over Réunion and the Southern Hemisphere.
while estimated NOx emission increases of 20–30 per cent 2.1.4 Renewable energy resources
Solar energy Despite receiving high solar irradiance, which averages 2 000 kilowatt hours per square meter per year, Africa’s installed capacity of large-scale solar energy is quite low, having increased from 40 megawatts in 2010 to 280 megawatts in 2013 (IEA 2014). Many rural areas in Africa are isolated, and this increases the cost of infrastructure for electricity distribution. As a result, photovoltaic (PV) and concentrating solar power (CSP) systems are an ideal solution for areas without grid connection. Africa’s potential solar energy output from PV and CSP is estimated at 6 567 terawatt hours and 4 719 terawatt hours per year, respectively (IRENA 2011) (More...3).
Wind energy
Africa has abundant wind energy sources, which could help the region to meet its future electricity demand and promote significant economic growth (Mas’ud et al. 2015), with positive health benefits. Wind energy markets in the region remain small, with an estimated 43 MW having been installed in sub-Saharan Africa. The low wind power installation accounts for 4 per cent of global installation, although projects to add 230 MW to the existing capacity are under consideration (Mas’ud et al. 2015).
Renewable energy forms such as wind power have not been a priority for Africa because of technological and funding challenges in a region that has to grapple with other pressing issues such as poverty and poor health provision. As costs related to renewables, wind technology in particular, continue to come down, Africa’s installed wind energy capacity is expected to grow to 3.9 gigawatts by 2020, a figure that is dwarfed by the projected global total of 610 gigawatts by 2020 (Mas’ud et al. 2015).
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