climate variability

Africa: tripling of anthropogenic pollution

Explosive demography, massive urbanization, anarchic deforestation: West Africa is facing major changes, which augur a tripling of anthropogenic pollution. (1) between 2000 and 2030. What will be the impact on the health of populations and ecosystems, but also on meteorology and climate? The European DACCIWA programme, which brings together 16 partners, including the CNRS, the University of Toulouse III - Paul Sabatier, etc., is focusing on this question. It will eventually make it possible to improve weather and climate forecasting in this little-studied region. While a major campaign of airborne and ground-based measurements took place at the beginning of the summer, the programme is delivering its first results: it shows in particular that a large part of the pollution comes from open-air landfills.
Ahe DACCIWA program (Dynamics-Aerosol-Chemistry-Cloud interactions in West Africa)10 billion, funded by the European Union and coordinated by the Karlsruher Institute for Technology in Germany, focuses on the links between weather, climate and air pollution in West Africa, from Côte d'Ivoire to Nigeria. It enables scientists for the first time to fully investigate the impacts of natural and anthropogenic emissions on the region's atmosphere and human health through a large-scale field campaign in June and July 2016.
The air along the Gulf of Guinea is a complex and unique mixture of different gases and aerosols. (2)These include monsoon winds laden with sea salt, Saharan winds carrying dust, forest and domestic fires, open dumps in cities, cohorts of offshore tankers, oil platforms and an aging fleet of cars, among others. At the same time, the multiple cloud layers that develop in this environment strongly influence weather and climate. The composition of the air and its influence on cloud formation and dissipation has never been studied in this region. Meteorological and climate models are therefore still incomplete with regard to aerosol-cloud interactions in a chemical environment as complex as that of the Gulf of Guinea.
Air pollution in Africa has been underestimated according to a Franco-Ivorian team, led by the CNRS aerology laboratory in Toulouse, which produced maps, country by country, for 2005 and estimated the evolution of air pollution for 2030. On the African continent, air pollution is mainly due to human activities. As explained by our colleagues from RFi AfricaAfter developing several scenarios, the researchers found that estimates of pollutant emissions, particularly in Central, West and East Africa, were significantly underestimated. According to the researchers, pollutant emissions are as high in African cities as in the heavily polluted capitals of other countries that were previously better documented, such as China, India and France. 
Today, if we consider all anthropogenic emission sources, the African continent represents between 5 and 20% of pollution on a global scale, depending on the particles or gases considered (soot carbon, organic carbon, sulphur dioxide, nitrogen dioxide, carbon monoxide). And if no action is taken, it could contribute between 20 and 50% in the coming years. A significant ratio due to the fact that elsewhere, these same emissions have already decreased.

Among the means implemented in the DACCIWA programme, three research aircraft have made it possible to monitor air pollution from ports and major coastal cities (Abidjan, Accra, Lomé, Cotonou, Lagos) inland.
The ATR 42, of the French Instrumental Aircraft Service for Environmental Research (CNRS/MétéoFrance/CNES), is one of the 3 research aircraft that have worked in a coordinated manner over the countries of the Gulf of Guinea (with the Falcon 20 of the German Space Agency (DLR) and the Twin Otter of the British Antarctic Survey). It carried more than two tons of in situ and remote sensing equipment. This airborne campaign documented the
It also provided information on regional sources of pollution such as biomass fires from the southern hemisphere or desert dust. Very localized sources were characterized by these operations (flares, industrial site, port) as well as natural emissions from vegetation. In the photo below, the plane flies over the port of Lomé (Togo). Sébastien Chastanet/LA/OMP/UPS

Significant resources were also deployed on the ground: for two months, three heavily instrumented sites in Ghana, Benin and Nigeria continuously measured clouds and many of the physical phenomena that contribute to their formation or dissipation. In addition, meteorological balloons were released several times a day throughout the region and ad hoc measurements of urban air pollution and health surveys were carried out in Abidjan (Côte d'Ivoire) and Cotonou (Benin).
The "supersite" of Savé (Benin). On the picture above is a balloon(in the foreground) and a rain radar (building with a
 dome). The Aerology Laboratory (CNRS/Université Toulouse III - PaulSabatier) installed a UHF radar, an instrumented tower for the
meteorology and atmospheric chemistry (photo on the right), and has put inis using a lightweight drone to measure the temperature and humidity of the air. Sébastien Chastanet/LA/OMP/UPS

The first results show, surprisingly, that a large part of the pollution is of organic origin, linked to the permanent combustion, at low temperature, in open-air landfills. The particles produced reduce the amount of solar radiation reaching the ground, modifying the diurnal evolution of temperature, wind and clouds, as well as atmospheric dynamics.
Until 2018, researchers will now analyse these data, supplemented by satellite observations, in order to propose an explanatory scheme of the interaction between atmospheric chemistry, aerosols, low cloud formation and dissipation, radiation balance and precipitation. The aim is to improve meteorological, climate and air quality models, which will support environmental policies for sustainable development in the region, and provide useful indications on the health consequences of air pollution.
Map of population density in the area of interest. From Côte d'Ivoire to Nigeria, a huge coastal megalopolis 2,000 km long is emerging. What will be the consequences on air quality, meteorology and climate?
© Robert Simmon, NASA's Earth Observatory/SEDAC, Columbia University

The French laboratories and services involved in this programme are :
- the Functional and Adaptive Biology Unit (BFA, CNRS/University Paris Diderot): evaluation of the toxicity of particles sampled in Abidjan and Cotonou (Armelle Baeza).
- the Centre national de recherches météorologiques (CNRM, CNRS/Météo-France): contribution to the payload for the measurement of "aerosols", on board the ATR 42.
- the Pierre Louis Institute of Epidemiology and Public Health (IPLESP, Inserm/UPMC): data collection in hospitals in Abidjan and Cotonou, carried out in collaboration with the BFA, in order to analyse the impact of air quality on health (Isabella Annesi-Maesano).
- the Aerology Laboratory (LA, CNRS/Université Toulouse III - Paul Sabatier): coordination of the field campaign on the instrumented supersite at Savé (Benin) and carrying out two air pollution measurement campaigns on urban sites in Côte d'Ivoire and Benin (Céline Mari).
- the Physical Meteorology Laboratory (LaMP, CNRS/Université Blaise Pascal): responsible for the ATR 42 payload for the measurement (in situ and remote) of chemical constituents, aerosol and cloud properties, radiation and atmospheric dynamics (Alfons Schwarzenboeck).
- the Atmospheres, Environments, Space Observations Laboratory (LATMOS, CNRS/UPMC/UVSQ): coordination of the airborne campaign conducted from Lomé (Togo) and weather forecasts in support of aircraft operations (Cyrille Flamant).
- the Dynamic Meteorology Laboratory (LMD, CNRS/Polytechnic School/UPMC/ENS of Paris): forecasting for atmospheric chemistry in support of aircraft operations, in coordination with the LA.
- the Observatoire Midi-Pyrénées (OMP, CNRS/IRD/Université Toulouse III - Paul Sabatier/Météo-France): creation of the DACCIWA Operation center website by the data department of the OMP, to gather and make available the "quick looks" of observations acquired in the field as well as the analyses of the different forecasting centers involved in the project. 
- the Service des avions français instrumentés pour la recherche en environnement (SAFIRE, CNRS/Météo-France/CNES): operator of the French research aircraft.
The DACCIWA project brings together 16 partners from 6 countries: in Germany, the Karlsruher Institut für Technologie and the German Space Agency (DLR); in the United Kingdom, the European Centre for Medium-Range Weather Forecasts, the Met Office, as well as the Universities of Leeds, York, Reading and Manchester; in Switzerland, the ETH-Zürich ; in Ghana, Kwame Nkrumah University of Science and Technology Kumasi; in Nigeria, Obafemi Awolowo University; in France, CNRS, Université Toulouse III - Paul Sabatier, Université Pierre et Marie Curie, Université Blaise Pascal - Clermont-Ferrand II, Université Paris Diderot. The University Félix-Houphouët-Boigny in Abidjan (Côte d'Ivoire) and the University of Abomey-Calavi in Cotonou (Benin) are also associated with the programme.

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(1) emitted by human activities.
(2) particles, solids and liquids in suspension


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