Helium in old porcelain: The historical variation of the He isotopic composition in air

Abstract

It is still debated whether there is a variation of the atmospheric ³He/⁴He ratio, due to the anthropogenic release of radiogenic ⁴He contained in fossil fuels, in modern era. In this study, we measured the He isotopic ratios in old Chinese and Japanese porcelains assuming that the old atmosphere might have been preserved in vesicles. The trapped noble gases are elementally but not isotopically fractionated. The ³He/⁴He ratios in some old Chinese porcelain are significantly higher than the present air value, indicating that recent human industrial activity might have affected the helium isotopic ratio of the atmosphere. Our result indicates that the rate of change in the atmospheric ³He/⁴He ratio was -0.034 ± 0.018 %/year (2σ) in the last 200 years. Results show that porcelain can be used as a time capsule of the paleoatmosphere during historical age.