Measurements and Quality Assurance
The DEBITS scientific activities are mainly based on measurements of precipitation chemistry to quantify wet deposition, as well as aerosol and gas concentrations in order to estimate dry deposition. The DEBITS stations are representative of the 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 a long-term timeseries of ground-based observations. The inclusion of data of urban sites in the DEBITS-II program is aimed at determining the impact of urbanisation and anthropogenic activities on the Earth System.
Wet deposition measurements are carried out using standardised rainwater sampling, preservation and chemical analyses procedures. Meteorological rain gauges are used for the evaluation of wet deposition at all DEBITS sites. To obtain comparable data sets for precipitation chemistry with a high quality standards, an experimental strategy comprised of:
- wet-only sampling on the event scale (samples taken only when rainfall occurs) preservation of the chemical content using a biocide or by freezing
- quality assurance of all samples using criteria from the US EPA concerning ionic and conductivity balances, as well as through annual analytical laboratory performance checks using the WMO protocol for chemical analyses
Quantification of dry deposition of gaseous species is carried out using passive sampling techniques. Measurements of biogeochemically important species such as SO2, NO2, NH4 (gas), HNO3, O3 and VOC’s are undertaken at all sites. Dry deposition of particles is estimated from either bulk measurements or from measurements in two size classes (PM 2.5 and PM 10.0). Air sampling is carried out using various filters, membranes and using standardised chemical analyses. Direct flux measurement methods, such as Eddy Correlation or Eddy Accumulation, which have been used in several field programs in tropical areas, provide estimates of deposition velocities suitable for determining dry deposition rates from the measured ambient concentrations at the DEBITS sites.