Comparison of Rainwater Silver Concentrations from Seeded and Non-seeded Days in León (Spain)

J L Sanchez, J Dessens, J L Marcos, J T Fernández


The long-term hail suppression projects arouse the public opinion's intrest in the levels of pollution that may be reached in the precipitation.  Even though the seeding material that is usually employed is AgI, and in spite of numerous references denying the toxicity of these emissions, it is easy to estimate the amount of AgI in rainwater, and the results obtained reassure the public opinion.  Within the hail suppression project corresponding to the acronym PALA (Plan for Hail Suppression Aims), which has been carried out in León (Spain) since 1986, there is a network of generators giving a total of nearly 200 grams of AgI per hour.  34 rain gages were employed to collect rainwater samples that have then been analyzed to determine the silver concentration.  The average concentration on seeding days in 4.6 ppb, which is well below toxic concentration levels.

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