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DEBITS: Deposition of Biogeochemically Important Trace Species Task Coordinators Dr. Kobus Pienaar, Convenor Dr. Corinne Galy, IDAF coordinator Dr. Paulo Artaxo, LBA coordinator Dr. Luciene Lara, LBA coordinator Dr. R. Balasubramanian, CAD coordinator Dr. Leong Chow Peng, CAD coordinator Dr. Gregory R. Carmichael, Modeling coordinator DEBITS II is presented as a new IGAC task, following the success of the first phase of DEBITS within the IGAC framework. It addresses the second of IGAC's overall science questions: to provide a fundamental understanding of the processes that control the distributions of chemical species in the atmosphere and their impact on global change and air quality1. I. Motivation and background Wet and dry deposition of chemical species to the earth’s surface plays an essential role in controlling the concentration of gases and aerosols in the troposphere. The chemical content of atmospheric deposition is the signature of several interacting physical and chemical mechanisms such as: emission and source amplitude; transport in and dynamics of the atmosphere; atmospheric chemical reactions; and removal processes. The study of deposition thus allows for tracing the temporal and spatial evolution of atmospheric chemistry and is a pertinent indicator for evaluating natural and anthropogenic influences. In regions where biogeochemical cycles are disturbed by human activities, atmospheric deposition can be either an important source of toxic substances or a source of nutrients for the ecosystems. Having an understanding of chemical deposition is therefore an essential aspect of a global interdisciplinary approach to developing a predictive capacity for the input of the main determinants into the functioning ecosystems. The IGAC programme was created in response to a growing international concern about
rapid changes in the global atmospheric composition and the impact of these changes on
mankind. One of the main successes for IGAC to date has been to highlight studies in
atmospheric chemistry in the Tropics, stressing the key importance that tropical
atmospheric chemistry has on the global composition of the atmosphere. Under phase I,
DEBITS also focussed on the tropical regions because:
II. Past and present activites In 1998, the scientific objectives of the original DEBITS plan were refocused as follows:
To fulfill these objectives, the first action of the DEBITS committee was to define a set of experimental and analytical protocols to assure data quality, and to secure the inter-comparison of the measurements of wet and dry deposits for all DEBITS stations. The participation of all DEBITS stations in the GAW laboratory intercomparisons and acceptance of the GAW data quality objectives and operating procedures is encouraged in order to facilitate the production of comparable data sets. The DEBITS scientific activities are mainly based on measurements of controlled precipitation chemistry to quantify wet deposition and aerosol and gas concentrations in order to estimate dry deposition. The DEBITS stations are representative at a regional scale and are specially equipped with instrumentation to measure or estimate atmospheric deposition parameters. Each has been created and maintained with the goal of producing long-term time-series. The organisational framework of DEBITS was established with the launch of three scientific programmes aimed at studying deposits in different regions: CAAP (Composition and Acidity of Asian Precipitation, 1990), IDAF (IGAC DEBITS Africa, 1994) and LBA in Amazonia (The Large Scale Biosphere Atmosphere Experiment in Amazonia, 1998). A map of the DEBITS network is presented in Figure 1.  DEBITS in Asia began in 1990 and was originally an IGAC task entitled “Composition
and Acidity of Asian Precipitation” (CAAP) initiated by the Department of Meteorology at
Stockholm University (MISU) and the Division for Atmospheric Research, CSIRO, Melbourne.
Within this activity support was provided, mainly from Sida (cf. Section VII), to a number
of countries in Asia to set up sampling stations. Workshops were supported to facilitate the
exchange of data on acidification in the region (such as the CAAP workshop in Bombay in 1992).
This work subsequently broadened to include the assessment of ecosystem sensitivity to acidic
depositions. Findings from this work have since been used to identify areas at risk from acidic
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 of the IGBP. 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 Sweden and Australia. The main objectives of CAD are:
In 2000, the CAD program emphasis was shifted to de-emphasize the rainwater acidity issue and expand the goal of including dry deposition measurements. DEBITS in Africa was created in 1994, with the launch of the IDAF (IGAC DEBITS AFRICA) program. The scientific objectives of the IDAF programmes were defined at the Yamoussoukro Workshop in Ivory Coast (December 1994). DEBITS/AFRICA has acknowledged the global importance of biomass burning, land use change and industrization resulting from rapid population growth. These activities lead to important anthropogenic emissions and to desertification, which may generate atmospheric reactive carbon, nitrogen, sulphur and dust, likely producing atmospheric acidity and acid depositions. These may result in adverse effects upon vegetation/soil/water systems and produce high levels of aerosol haze, which would in turn 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:
Ten IDAF sites, representative of the greater African ecosystems, were operating in 2002 and several meetings have been organized (Abidjan 1995, Toulouse 1998 and 2001). African scientists in charge of monitoring stations also visited Toulouse (1 to 3 months). A database that includes a description of the stations and chemical data on rainfall, gaseous species and particles is available on http://www.medias.obs-mip.fr/idaf/. DEBITS in Amazonia is one of the activities comprising the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA; http://lba.inpa.gov.br/lba/indexi.html). In addition to looking at the dry and wet deposition at several sites in Amazonia, DEBITS is also looking at deposition patterns in the industrialized 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 programme, four wet and dry deposition sampling stations were set up in Brazil; in addition, the station of Petit-Saut (French Guiana) was implemented within the IDAF framework in cooperation with French researchers. One aspect these five deposition stations' foci is to determine the importance of the atmospheric part of the nutrient cycle from natural and secondary forests and managed lands. Observations at five DEBITS sites span gradients of intense land use and climate, and each now has observations over a period of several years. These ongoing, localized data are complemented by periodic large-scale airborne observations and intensive ground based experiments. Important results have shown the crucial role of the vegetation cover in determining aerosol and CCN concentrations, as well as water balances in the region and the many potential feedbacks between the ecosystem and the physical and chemical climate of the region. III. Future activites Within the new structures established for IGBP Phase II, the DEBITS science community plans to adopt a twofold approach:
Finally, the historical links between DEBITS and the WMO GAW program and WMO regional networks will be maintained and strengthened through DEBITS becoming a "contributing partner" of this initiative 4. IV. Principles and specific scientific questions The underlying principles of the new DEBITS II task is to promote and facilitate international
atmospheric deposition research that will lead to a better understanding of responses and feedbacks
within the Earth System. The task is driven by scientific questions related to global atmospheric
chemistry, and its activities will be focused in regions of high impact on sensitive ecosystems and
human health. The specific scientific questions being addressed under the second phase of DEBITS are:
V. Quality assurance and methodologies The scientific activities of DEBITS are mainly based on quality-controlled measurements of precipitation chemistry to quantify wet deposition, as well as aerosol and gas concentrations to estimate dry deposition. DEBITS stations, representative at the regional scale and specially instrumented to measure or estimate atmospheric deposition parameters, have to be maintained or created for long-term time-series. Additional measurements, permitting a better estimate of depositions, will require field experiments dedicated to atmospheric chemistry at the regional scale. The inclusion of data of mega-pole sites in DEBITS II is aimed at determining the impact of urbanisation and anthropogenic activities in general on the Earth System. Wet deposition measurements will be continued using a standardised rainwater
sampling, preservation and chemical analysis procedure. Meteorological rain gauges are used for the
evaluation of wet deposition at all the sites. To obtain comparable data sets for precipitation
chemistry with a high quality assurance, an experimental strategy comprised of:
will be employed. Dry deposition quantification for gases and particulates will require the continued monitoring of concentrations by passive gas sampling for SO2, NO2, NH4 (gas), HNO3, O3 and VOC's. In the same way, dry deposition of particles will be estimated from either from bulk measurements or from measurements in two size classes (PM 2.5 and PM 10.0) by sampling air on membranes and using standardised chemical analysis. Direct flux measurement methods, such as Eddy Correlation or Eddy Accumulation, which have been used in field programs in tropical areas as well as other regions, will provide a data set of deposition velocities suitable for determining dry deposition rates from the measured ambient concentrations at the DEBITS sites. VI. Data management and archiving In consultation with contributing partners and potential users, participating scientists in the new
DEBITS II task will:
Moreover, the DEBITS II programme plans to initiate a DEBITS web site that will include general information and a meta-data base using the ISO 19115 format. This web site will have a description of the measurement sites, the experimental methodologies of the DEBITS network and a list of general documentation concerning atmospheric deposition and integrated results produced by the DEBITS II activity. The DEBITS web site will be mirrored in the web sites of the three core programmes (CAD, IDAF and LBA). For the scientific community not linked to Internet, a CD-ROM will be also produced. VII. Educational and Capacity Building DEBITS has a proud record of capacity building in the developing countries. Educational and capacity
building activities will be continued by:
VIII. Timetable The timetable of DEBITS is in accordance with the main goal of DEBITS to create, maintain and expand a long-term time-series of measurements of controlled precipitation chemistry to quantify deposition. The activities included in the three regional programmes (IDAF, CAD and LBA) are all aimed at providing data that would benefit studies on interannual-to-decadal variability of deposition fluxes of biogeochemically important trace species. In the new phase of DEBITS II, special emphasis will be placed on the synthesis of data already collected in previous phases as well as the inclusion of new parameters and insights into future studies (e.g. the inclusion of carbonaceous species, aerosols and particles). This action of DEBITS will be synchronised with scheduled bi-annual IGAC conferences in order to create sufficient time for bi-annual regional workshops and meetings. In agreement with the philosophy outlined above, the following time schedule has been drawn-up by
the Coordinating Committee:
Within the regional programs, various enhanced monitoring and data analysis activities is planned to improve the understanding of deposition processes and impacts on a regional scale. DEBITS scientists will also participate in special field campaigns focused on addressing regional specific needs and questions (e.g. participate in the AMMA task in Africa). IX. Milestones The following milestones are considered to be important in the new phase of DEBITS:
These milestones will be assessed by the number and impact of papers generated by participating scientists. The support given by DEBITS to other shorter-term programmes like AMMA and others are also regarded as important. X. Publication policy The DEBITS science community will actively participate and support the publication of international and multi-disciplinary research results. The added value of collaborating on a global basis within the IGAC framework is one of the main driving forces of this task. Although individual and regional publication will be encouraged, global synthesis of data and intercomparisons will add a lot of value to all participants and the CC will be responsible for driving these actions. It also serves the purpose of international capacity building by co-authoring papers of high quality. It is planned to prepare a significant number of such joint papers during each of the scheduled workshops to be publish in international accredited journals like Atmospheric Environment, Journal of Atmospheric Chemistry, Water, Air and Soil Pollution, Environmental Science and Technology, Tellus and other relevant journals. XI. Task Coordinators and Steering Committee The DEBITS Task coordinators are (contact information given above): References 1http://www.igac.noaa.gov/aboutus.php 2IGAC newsletter no. 27, DEBITS special issue, January 2003, IGACtivities Newsletter. 3J.P Lacaux et al, Wet depositions in the tropics, Chapter 2 “Biosphere Atmosphere Interactions” Part 2.7 : pp53-55, An Integration and Synthesis of a Decade of Tropospheric Chemistry Research, Series: Global Change - The IGBP Series , Brasseur, Guy P.; Prinn, Ronald G.; Pszenny, Alexander A.P. (Eds.), 2003, XIV, 300 p. 131 illus., Hardcover. 4http://www.wmo.ch/web/arep/gaw/gaw_home.html 
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