NON-RAIN DEPOSITION SIGNIFICANTLY MODIFIES RAIN SAMPLES AT A COASTAL SITE

Rain water sampling in marine areas was undertaken by four groups work ing independently at the same lime at the same place. The analytical r esults of the samples collected exhibit large variations and the main cause of these variations is the ''non-rain deposition'' as sea salt d uring the rain itself. The collected water is a mixture of rain water and variable amounts of more concentrated sea salt transported by the wind. This non-rain deposition is influenced by the exposure geometry of the sampler to the wind flow. Because sample conductivity and pH we re measured using exactly the same protocol each time, a quantitative model based on simple conductivity and pH measurements is proposed to compute the amount of dissolved sea salt within samples collected unde r marine conditions. The acid balance of the rain water appears to be not influenced by this non rain deposition. Conclusions given by this work should be taken into account to ensure the data quality of rain s ampling and analysis, especially if joint comparative experiments are conducted at different sites. (C) 1998 Elsevier Science Ltd. All right s reserved.