Precipitation samples are taken for all rainfall events using automatic precipitation collectors specifically designed for the IDAF network. The samples are analysed for:
- pH, Conductivity, major Inorganic and Organic ions:
(Cl- , NO3- , SO42-, HCO3- , CO32-, Na+, NH4+, K+, Mg2+, Ca2+, HCOOH, CH3COOH, C2H5COOH)
The automatic precipitation collectors function with a high degree of cleanliness, with a separate polyethylene bag being used for each precipitation event. A detector automatically opens the aperture, whose area of collection is 225cm2 when rainfall occurs and hermetically seals the collector when precipitation stops. This prevents aerosols from being deposited in the collector outside of precipitation events.
Greiner tubes are used to collect 50cm3 from each sample. These tubes are then frozen or refrigerated before analysis at the Laboratoire d’Aérologie. The preservation of the rainwater samples is an important problem because of microbial degradation which can modify the chemical composition of the sample collected. Samples are collected for a minimum of 90% of rain events representative of a rainy season.
pH, conductivity and ion chromatography analyses are submitted to the WMO quality controls and he US EPA/ WMO criteria for ionic balance are applied and presented in the database for each sample.