Corinne Jambert

Gaseous emissions and oxygen consumption in hydroelectric dams: A case study in French Guyana

Methane, carbon dioxide, and hydrogen sulfide emissions from the hydroelectric dam of Petit Saut on the Sinnamary River in French Guyana have been measured over a 2 year period. Since the beginning of the reservoir filling (January 1994), 300 km 2 of tropical forest have been submerged. Emissions of CH 4 by diffusion and by bubbling into the atmosphere or by degassing of the water released into the river, as well as the stock of dissolved gases in the lake, and their temporal evolutions were determined. Maximum emissions of 800 t CH per day were reached in February 1995, corresponding to dissolved CH 4 concentrations of 14 mg 4 L -1 in the water column. The biological oxidation of methane results in a strong oxygen consumption in lake and river waters. Total emissions of CH 4 and CO 2 from January 1994 to December 1995 were calculated from the whole data set, which also allows us to calculate the total carbon loss since reservoir filling. About 10% of the carbon stored in soil and vegetation was released in gaseous form within 2 years.

Nitrogen compound emissions from fertilized soils in a maize field pine tree forest agrosystem in the southwest of France

The use of nitrogen fertilizers in agriculture is a significant source of reactive nitrogen compounds for the atmosphere. Emissions of NO, NH3, and N2O were measured on irrigated maize fields, on acidic podzols, set up in a large pine tree forest system in the southwestern part of France. Measurements were carried out over a yearly period: before, during, and after fertilization. Trace gas emissions appear to be strongly linked to soil characteristics and to the type of fertilizer and application procedures used. All emissions are strongly enhanced after fertilizer application, although NO and N2O emissions are observed all year long. No emission was observed on forest soils which only constitute an atmospheric NO2 sink. The imbalance of the nitrogen budget (up to 100 kg N ha−1) might be explained by gaseous emissions into the atmosphere, watertable pollution by nitrate and ammonium ions remaining very low. This is one of the peculiarities of this agrosystem.

Measurements of nitric oxide and ammonia soil fluxes from a wetsavanna ecosystem site in West Africa during the DACCIWA fieldcampaign

Biogenic fluxes from soil at a local and regional scale are crucial to study air pollution and climate. Here we present field measurements of soil fluxes of nitric oxide (NO) and ammonia (NH3) observed over four different land cover types, i.e. bare soil, grassland, maize field, and forest, at an inland rural site in Benin, West Africa, during the DACCIWA field campaign in June and July 2016. At the regional scale, urbanization and a massive growth in population in West Africa have been causing a strong increase in anthropogenic emissions. Anthropogenic pollutants are transported inland and northward from the megacities located on the coast, where the reaction with biogenic emissions may lead to enhanced ozone production outside urban areas, as well as secondary organic aerosol formation, with detrimental effects on humans, animals, natural vegetation, and crops. We observe NO fluxes up to 48.05 ngN m−2 s−1. NO fluxes averaged over all land cover types are 4.79± 5.59 ngN m−2 s−1, and maximum soil emissions of NO are recorded over bare soil. NH3 is dominated by deposition for all land cover types. NH3 fluxes range between −6.59 and 4.96 ngN m−2 s−1. NH3 fluxes averaged over all land cover types are−0.91±1.27 ngN m−2 s−1, and maximum NH3 deposition is measured over bare soil. The observations show high spatial variability even for the same soil type, same day, and same meteorological conditions. We compare point daytime average measurements of NO emissions recorded during the field campaign with those simulated by GEOS-Chem (Goddard Earth Observing System Chemistry Model) for the same site and find good agreement. In an attempt to quantify NO emissions at the regional and national scale, we also provide a tentative estimate of total NO emissions for the entire country of Benin for the month of July using two distinct methods: upscaling point measurements and using the GEOS-Chem model. The two methods give similar results: 1.17± 0.6 and 1.44 GgN month−1, respectively. Total NH3 deposition estimated by upscaling point measurements for the month of July is 0.21 GgN month−1.

A Modelling Perspective of the Summer 2013 and 2014 ChArMEx/SAFMED Chemistry Intensive Campaigns: Origin of Photo-Oxidant and Aerosol Formation over the Western Mediterranean

During summers 2013 and 2014, two three weeks intensive campaign took place over the western Mediterranean basin in order to investigate photo-oxidant and aerosol sources over the region. Within the frame of the MISTRALS/ChArMEx (Chemistry-Aerosol Mediterranean Experiment) program and the ANR/SAFMED (Secondary Aerosol Formation in the MEDiterranean) project, this campaign included an extensive experimental set-up based on ground-based, balloon-borne, aircraft and satellite measurements. In this paper, a modeling perspective of the campaign is given, based on simulations with the regional chemistry-transport model, CHIMERE, in a configuration shaped for the Mediterranean region. Major sources of photo-oxidants, and aerosols are addressed: long range transport from continental Europe, pollution build-up from shipping emissions, marine emissions, organic aerosol formation from biogenic and anthropogenic VOC emissions, dust emissions.