A simple and cost‐effective sample preparation and storage method for stable isotope analysis of atmospheric CO2 for GasBench II/continuous flow isotope ratio mass spectrometry

RATIONALE: The stable isotope compositions of atmospheric CO₂ can provide useful insight into various geochemical processes and carbon cycles on Earth, which is critical for understanding of Earth's changing climate. Here, we present a simple and cost-effective analytical method for the collection and measurement of carbon and oxygen isotope compositions of atmospheric CO₂. METHODS: Air samples of ~150 mL were collected individually or collectively using our simple active air collection system and then extracted on a vacuum purification line to remove noncondensable gases and atmospheric water vapor. The efficiency of removing atmospheric water vapor was tested by using a magnesium perchlorate desiccant trap and a dry ice/ethanol trap. Lastly, a "J-Cut tube sealing/cracking method" was developed to store and transfer purified atmospheric CO₂ to the GasBench II and CF-IRMS system for δ¹³C and δ¹⁸O measurements. RESULTS: The collective active air collection method combined with the full sample air extraction method for a 3-min transfer time or "Full 3m TE" yields the best analytical precision of 0.07‰ (δ¹³C) and 0.04‰ (δ¹⁸O). Removing atmospheric water vapor from air samples is not necessary for δ¹³C, but essential for δ¹⁸O measurements. The J-Cut tube sealing/cracking method shows a near 100% effectiveness for the storage and transfer of atmospheric or any CO₂. CONCLUSIONS: A simple and cost-effect method was developed for the collection, purification, storage, and isotopic analysis of indoor/outdoor atmospheric CO₂ samples for general users. This method utilizes a popular headspace gas sample preparation system for CF-IRMS and an easy-to-build vacuum purification line without involving complex and high-cost devices for the preparation of atmospheric CO₂.