Cost-effective off-grid automatic precipitation samplers for pollutant and biogeochemical atmospheric deposition

An important transport process for particles and gases from the atmosphere to aquatic and terrestrial environments is through dry and wet deposition. An open-source, modular, off-grid, and affordable instrument that can automatically collect wet-deposition samples allows for more extensive deployment of deposition samplers in fieldwork and would enable more comprehensive monitoring of remote locations. Precipitation events selectively sampled using a conductivity sensor powered by a battery-based supply are central to off-grid capabilities. The prevalence of conductive precipitation - that which initially contains high solute levels and progresses through trace-level concentrations to ultrapure water in full atmospheric washout - depends on the sampling location but is ubiquitous. This property is exploited here to trigger an electric motor (via limit switches) to open and close a lid resting over a funnel opening. The motors are operated via a custom-built and modular digital logic control board, which has a low energy demand. All components, their design and rationale, and their assembly are provided for community use. The modularity of the control board allows the operation of up to six independent wet-deposition units, such that replicate measurements (e.g., canopy throughfall) or different collection materials for various targeted pollutants can be implemented as necessary.