Adapting Automatic Water Samplers for the Isotopic Study of Rainfall at High Temporal Resolution

Area of Science:

• Hydrology
• Atmospheric Science
• Analytical Chemistry

Background:

• Stable water isotopes in precipitation serve as crucial tracers for atmospheric processes.
• High temporal resolution isotopic studies require automatic rain samplers, which are often costly to build.
• A commercial water autosampler was modified to enable intra-event precipitation sampling and prevent post-sampling evaporation.

Purpose of the Study:

• To develop a low-cost method for high-resolution precipitation sampling for isotopic analysis.
• To modify a commercial water autosampler to prevent post-sampling evaporation.
• To assess the suitability of the modified autosampler for intra-event rainfall sampling.

Main Methods:

• Modified a commercial water autosampler by reducing bottle volume and opening area.
• Conducted evaporation tests to determine minimum sample volumes for negligible isotopic fractionation.
• Investigated the impact of autosampler air moisture saturation on sample integrity.
• Analyzed samples using dual-inlet isotope ratio mass spectrometry and cavity ring-down spectroscopy.

Main Results:

• Evaporative enrichment of heavy isotopes is negligible for samples >10 mL compared to analytical uncertainty.
• Intentional saturation of the autosampler's atmosphere significantly reduces post-sampling evaporation.
• The modified autosampler is suitable for intra-event rainfall sampling under specific conditions.

Conclusions:

• Low-cost, high-resolution precipitation sampling for isotopic analysis is now feasible.
• Intentional air saturation of the sampler effectively prevents post-sampling evaporation, a novel approach.
• Open-access instructions for sampler modification are available, facilitating scientific community replication.