Non-rain deposition significantly modifies rain samples at a coastal site

Rain water sampling in marine areas was undertaken by four groups working independently at the same time at the same place. The analytical results of the samples collected exhibit large variations and the main cause of these variations is the “non-rain deposition” as sea salt during 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 were 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 under 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 sampling and analysis, especially if joint comparative experiments are conducted at different sites.