The DEBITS science community supports an integrated approach to atmospheric chemistry studies within the context of the IGAC program. Strong networking and data-sharing with other IGBP program such as iLEAPS (Integrated Land-Ecosystem Atmosphere Study), the GLP (Global Land Project) and SOLAS (Surface Ocean Lower Atmosphere Study) are maintained. This coordinated approach deals with (1) atmospheric chemistry studies at the interface of continental and marine environments and (2) associated impact studies. An integrated social, economic and physico-chemical approach to earth systems maximises the value to society of large international research efforts.
The organisational framework of DEBITS was established with the launch of three scientific programs aimed at studying atmospheric deposition processes in different the tropical regions: CAD (Composition of Asian Deposition), IDAF (IGAC-DEBITS AFrica) and LBA (Large-scale Biosphere-atmosphere experiment in Amazonia). The activities included in the three regional programs are aimed at providing data that benefits studies concerning the interannual-to-decadal variability of deposition fluxes of biogeochemically important trace species. Within the regional programs, various enhanced monitoring and data analysis activities have been and continue to be carried out in order to improve the understanding of deposition processes and impacts on a regional scale (e.g. special field campaigns focused on addressing regional specific needs and questions such as the AMMA task in West Africa).
CAD - Composition of Asian Deposition
DEBITS in Asia began in 1990 and was originally an IGAC task entitled "Composition and Acidity of Asian Precipitation" (CAAP). The project was initiated by the Department of Meteorology at Stockholm University (MISU) and the Division for Atmospheric Research at CSIRO, Melbourne. Support was provided to a number of countries in Asia to set up sampling stations and several workshops were organised to facilitate the exchange of data on acidification in the region (such as the CAAP workshop in Bombay, 1992). This work subsequently broadened to include the assessment of ecosystem sensitivity to acid deposition. Findings from this work have since been used to identify areas at risk to acid deposition. After the 1998 CAAP workshop, it was decided that the network should also consider dry deposition and be renamed the Composition of Asian Deposition (CAD ) forming part of the IGAC/DEBITS activities. Leadership of the network has been transferred to Asian institutions, with a steering committee comprised of representatives from Malaysia, Singapore, Japan and India as well as from Sweden and Australia. The main objectives of CAD are:
- to determine, primarily through measurements, the atmospheric removal rates of biogeochemically important trace species through dry and wet deposition processes in South and South-East Asia
- to establish at regional scale atmospheric budgets of key elements (S, N, Ca)
- to relate the deposition fluxes to the sensitivity of soils and surface waters
- to obtain data for testing regional transport models of sulphur and nitrogen pollutants
IDAF - IGAC DEBITS in AFrica}
DEBITS in Africa was created in 1994, with the launch of the IDAF (IGAC DEBITS in AFrica) program. The scientific objectives of the IDAF program were defined at a workshop held in Yamoussoukro, Ivory Coast. The IDAF project has acknowledged the global importance of biomass burning, land use change and industrialisation resulting from rapid population growth on the African continent. These activities lead to important anthropogenic emissions and to desertification, which may generate atmospherically reactive carbon, nitrogen, sulphur and dust, which in turn likely result in atmospheric acidity and acid deposition. These may result in adverse effects upon vegetation, water and soil systems as well as producing high levels of aerosol haze, which may exert a significant forcing on global climate and have other related effects, such as increasing the level of tropospheric ozone.
The IDAF objectives, which consider the contributions of biomass burning and desertification (soil dust) to atmospheric chemistry specifically in Africa, were defined as follows:
- to estimate, from measurements of wet and dry deposition fluxes, important chemical species (especially N, C (i.e. Organic Aerosol) and S) at regionally representative sites
- to identify the relative contributions of natural and anthropogenic sources to these deposition fluxes
Ten IDAF sites, representative of the major African ecosystems, continue to operate on the continent. Workshops have been organized (Abidjan 1995, Toulouse 1998 and 2001) within the context of the IDAF program and several African scientists in charge of the monitoring sites have also visited Toulouse (1 to 3 months). A database that includes a description of the stations and chemical data on rainfall as well as gaseous and aerosol species is available on the IDAF website.
LBA - Large-scale Biosphere-atmosphere experiment in Amazonia
DEBITS in Amazonia is one of the activities comprising the Large-scale Biosphere-atmosphere experiment in Amazonia (LBA ). In addition to looking at the dry and wet deposition at several sites in Amazonia, DEBITS also considers deposition patterns in the industrialised southern part of Brazil. Amazonia is a key tropical region experiencing strong pressure in terms of land use and land cover changes. The LBA experiment is a large (more than 700 researchers) and long-term (about 10 years) research effort aimed at better understanding this key tropical ecosystem. Within the scope of the LBA program, four wet and dry deposition sampling stations have been set up in Brazil. In addition, the station of Petit-Saut (French Guiana) has been implemented within the IDAF framework in cooperation with French researchers.
These five DEBITS observation sites focus on determining the importance of the atmospheric contribution to the nutrient cycle of natural and secondary forests as well as managed lands. The measurement sites span gradients of different land use and climate, and have each maintained observations for several years. These ongoing, localised measurements are complemented by periodic, large-scale airborne observations in association with intensive ground-based experiments.
Important results have shown the crucial role of vegetation cover in determining aerosol and CCN (cloud condensation nuclei) concentrations, as well as affecting the hydrological balance in the region and the many potential feedbacks between ecosystems and the physical and chemical climate of the region.