Issue 27 Jan 2003 - IGAC Project

ically important trace species by dry and wet
depositional processes
• to investigate the chemical and physical factors that
regulate deposition fluxes
To accomplish these objectives, the first actions of the
DEBITS committee included the definition of experimental
and analytical protocols to ensure data quality (Box 1)
and the establishment of guidelines for inter-comparisons
of wet and dry deposition measurements for all DEBITS
stations.
In 1998, the scientific objectives of DEBITS were redefined
and as follows:
• to determine, at the regional scale, and mainly through
measurements, the atmospheric removal rates of
biogeochemically important trace species by dry and
wet deposition
• to resolve atmospheric budgets of key elements (S, N
Ca, C1 …) at the regional scale
• to ascertain the chemical and physical factors that
regulate deposition fluxes and to develop
parameterizations to be integrated into regional and
global atmospheric chemistry models
The organizational framework of DEBITS was established
with the initiation of three scientific programs in
important tropical regions: Composition and Acidity of
Asian Precipitation (CAAP) in 1990, IGAC DEBITS
Africa (IDAF) in 1994, and the Large Scale Biosphere
Atmosphere Experiment in Amazonia (LBA) in 1998. A
map of the DEBITS network is presented in Figure 1.
The CAAP program
CAAP began in 1990 following the publication of
Acidification in Tropical Countries by Rodhe and Herrera
(1988). At that time, it was acknowledged that there was a
major gap in our knowledge of deposition in Asia. This was
particularly true for high quality monitoring data and
regionally representative deposition data. Indeed, most of
the existing wet deposition studies had been limited to
urban areas. The main goals of CAAP were:
• to quantify the wet deposition component of the
atmospheric cycles of nutrients such as S,
N, C, P and sea salt
• to assess the current rate of rainwater acidity
throughout the region and to identify the
acid/basic species involved
CAAP has organized workshops within the region several
times during the past decade including Singapore in
1990, Bombay in 1992, and Bangkok in 1998. The purpose
of these meetings was to discuss the achievements of the
program up to that time and to propose future goals. These
included the measurement of the chemical composition of
precipitation and the surface air concentration of reactive
trace gases and aerosol particles from which dry deposition
can be estimated. Additional agenda items included the discussion
of procedures for quality control, the representativeness
of measurement stations and the publication of
results.
Box 1 – DEBITS experimental and
analytical protocols
DEBITS measurements require the adoption of standardized rainwater sampling, preservation and chemical analysis. To
obtain comparable and high quality data sets for precipitation chemistry, a standard experimental strategy was established
which includes:
• wet-only sampling for a specific event or a daily basis,
• efficient preservation of chemical content
using a biocide or freezing
• use of U.S. Environmental Protection Agency criteria based
on ionic and conductivity balances,
• annual analytical laboratory performance check with WMO
protocols for chemical analysis
Dry deposition measurements require measurement of gaseous concentrations by passive gas sampling for S0 2 , N0 2 ,
NH 3 , HN0 3 and 0 3 . Dry deposition of particles will be estimated from PM 10 sampling, or in two size classes (fine and
coarse modes), on membrane filters followed by chemical analysis.
IGACtivities 3