title: C4 plant isotopic composition (delta13C) evidence for urban CO2 pollution in the city of Cotonou, Benin (West Africa).
abstract: The carbon isotopic composition (delta13C) of plants can reveal the isotopic carbon content of the atmosphere in which they develop. The delta13C values of air and plants depend on the amount of atmospheric fossil fuel CO2, which is chiefly emitted in urban areas. A new indicator of CO2 pollution is tested using the delta13C variation in a C4 grass: Eleusine indica. A range of about 4 per thousand delta units was observed at different sites in Cotonou, the largest city in the Republic of Benin. The highest delta13C values, from -12 per thousand to -14 per thousand, were found in low traffic zones; low delta13C values, from -14 per thousand to -16 per thousand, were found in high traffic zones. The amount of fossil fuel carbon assimilated by plants represented about 20% of the total plant carbon content. An overall decrease in plant delta13C values was observed over a four-year monitoring period. This decrease was correlated with increasing vehicle traffic. The delta13C dataset and the corresponding geographical database were used to map and define zones of high and low 13C-depleted CO2 emissions in urban and sub-urban areas. The spatial distribution follows dominant wind directions, with the lowest emission zones found in the southwest of Cotonou. High CO2 emissions occurred in the north, the east and the center, providing evidence of intense anthropogenic activity related to industry and transportation.
authors.affiliation: UMR Microbiologie et Géochimie des Sols INRA, Université de Bourgogne, Centre des Sciences de la Terre, 6 Bd Gabriel, 21000 Dijon, France.
authors.forename: Nelly C
authors.initials: NC
authors.lastname: Kèlomé
authors.forename: Jean
authors.initials: J
authors.lastname: Lévêque
authors.forename: Francis
authors.initials: F
authors.lastname: Andreux
authors.forename: Marie-Jeanne
authors.initials: MJ
authors.lastname: Milloux
authors.forename: Lucien-Marc
authors.initials: LM
authors.lastname: Oyédé
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution; D001541:Benin; D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes / Q000032:analysis*; D002947:Cities; D031748:Eleusine / Q000737:chemistry* / Q000378:metabolism; D004784:Environmental Monitoring / Q000379:methods; D001335:Vehicle Emissions
chemical_list: D000393:Air Pollutants; D002247:Carbon Isotopes; D001335:Vehicle Emissions; D002245:Carbon Dioxide