Science Advisory Group - Atmospheric Deposition

The Science Advisory Group for Total Atmospheric Deposition (SAG-TAD) is one of seven SAGs that provide advice and guidance for the Global Atmosphere Watch Programme. The SAG-TAD replaces the SAG for Precipitation Chemistry (SAG-PC). The recently published Global Assessment of Precipitation Chemistry and Deposition demonstrated the importance of total (wet plus dry) atmospheric deposition in characterizing exchange processes between the atmosphere and earth surface. This led the SAG-PC to recommend that the group broaden its focus from precipitation chemistry to total atmospheric deposition and change its name to the SAG-TAD. The SAG-TAD is better able to provide comprehensive advice and guidance on issues such as critical loads or evaluation of model-derived estimates of total atmospheric deposition.

At WMO headquarters in Geneva in early 2017, the SAG-TAD held a workshop on combining atmospheric deposition measurements with model estimates of deposition to produce global maps of atmospheric gas and aerosol concentrations as well as wet, dry, and total deposition. Workshop proceedings have been published as a GAW report entitled, Global Atmosphere Watch Workshop on Measurement-Model Fusion for Global Total Atmospheric Deposition (MMF-GTAD).

Members of the SAG-TAD contribute expertise in such areas of atmospheric chemistry and deposition as (1) scavenging of gases and particles both during and in the absence of precipitation, (2) precipitation chemistry sampling and analysis, (3) gas and aerosol sampling and analysis, and (4) wet and dry deposition fluxes and loads. Nominated by the WMO, SAG-TAD members assist in the management and implementation of the GAW Atmospheric Deposition Programme.

Below is a summary of the role and responsibilities of the SAG-TAD in three areas: Operation, Organization, and Research.


  1. Archive global precipitation chemistry and deposition data and metadata and enable users to access data on-line via the World Data Centre for Precipitation Chemistry.
  2. Provide data sets for user communities such as atmospheric modellers and ecosystem effects researchers.
  3. Harmonize and improve methods for precipitation chemistry and deposition measurements by
    1. promulgating updated guidelines, data quality objectives and standard operating procedures for sampling and analysis; and
    2. promoting the Quality Assurance-Science Activity Centre’s Inter-laboratory Comparison Studies.
  4. Assist with the implementation of new sites, especially in areas poorly represented.


  1. Coordinate with other SAGs and other scientific activities such as ambient gas and aerosol monitoring, atmospheric modelling, ecosystem effects studies, climate research, etc.
  2. Provide information on atmospheric deposition and measurements in a form readily understood by scientists and non-scientists alike.
  3. Support training and promote capacity-building activities.
  4. Seek and secure support for SAG-TAD activities.


  1. Quantify spatial and temporal trends in precipitation composition and total deposition on regional and global scales.
  2. Develop, improve, and apply inferential methods to estimate dry deposition.
  3. Pursue measurement-model fusion methodologies to estimate total deposition.
  4. Improve understanding of atmospheric deposition of chemical species of current and emerging interest (e.g. organic acids, black carbon, metals, phosphorus, mercury, nitrogen).