Modeling the dynamic behavior of a droplet evaporation device for the delivery of isotopically calibrated low-humidity water vapor

Abstract. A simple model is presented that gives a quantitative description of the dynamic behavior in terms of water concentration (humidity) and isotope ratios of a low-humidity water vapor generator. The generator is based on the evaporation of a nL-droplet produced at the end of syringe needle by balancing the inlet water flow and the evaporation of water from the droplet surface into a dry air stream. The humidity level is adjusted by changing the speed of the high-precision syringe pump and, if needed, the dry air flow. The generator was developed specifically for use with laser-based water isotope analyzers in Antarctica, and recently described in Leroy-Dos Santos et al. (2020). Apart from operating parameters such as temperature, pressure, water and dry air flows, the model has as "free" input parameters the water isotope fractionation factors and the evaporation rate. We show that the experimental data constrain these parameters to physically realistic values that are in reasonable to good agreement with literature values where available.