Testing and development of a new precipitation gauge for chemical analysis

Abstract

Representative sampling of precipitation above ground is very difficult because the sampler itself affects the trajectory of the meteor. If chemical analysis of the precipitation is of interest, the sampling has to be made well above the ground. Samplers made of suitable material but not of optimal aerodynamical shape are traditionally used for collecting precipitation for chemical analysis by environmentalists worldwide. The obtained concentration is multiplied by the precipitation amount to obtain the wet deposition. Sometimes the precipitation amount from the same sampler that collects precipitation for chemical analysis is used and sometimes it is obtained from a standard gauge or from model calculations. Even if the material in the sampler is inert with respect to the ions analysed, the concentration can be wrong. If the sampling efficiency varies with time (due to changes in wind speed or droplet size), the precipitation weighted average concentration will not be correct. A sampler consisting of a snow sack in a wind protective tube has been modified in several steps to resemble a sampler used by meteorologist for measuring the precipitation amount on a daily basis. The two samplers measured similar precipitation amounts when a thinner rim was introduced on top of the tube containing the snow sack.Representative sampling of precipitation above ground is very difficult because the sampler itself affects the trajectory of the meteor. If chemical analysis of the precipitation is of interest, the sampling has to be made well above the ground. Samplers made of suitable material but not of optimal aerodynamical shape are traditionally used for collecting precipitation for chemical analysis by environmentalists worldwide. The obtained concentration is multiplied by the precipitation amount to obtain the wet deposition. Sometimes the precipitation amount from the same sampler that collects precipitation for chemical analysis is used and sometimes it is obtained from a standard gauge or from model calculations. Even if the material in the sampler is inert with respect to the ions analysed, the concentration can be wrong. If the sampling efficiency varies with time (due to changes in wind speed or droplet size), the precipitation weighted average concentration will not be correct. A sampler consisting of a snow sack in a wind protective tube has been modified in several steps to resemble a sampler used by meteorologist for measuring the precipitation amount on a daily basis. The two samplers measured similar precipitation amounts when a thinner rim was introduced on top of the tube containing the snow sack