H <sub>2</sub> in Antarctic firn air: Atmospheric reconstructions and implications for anthropogenic emissions
John D. Patterson, Murat Aydın, Andrew M. Crotwell, Gabrielle Pétron, Jeffrey P. Severinghaus, Paul B. Krummel, R. L. Langenfelds, E. S. Saltzman
Abstract
Significance Atmospheric molecular hydrogen (H 2 ) levels influence the lifetime of greenhouse gases and the levels of tropospheric ozone. The extent to which human activities have influenced the global H 2 budget is not well established due to our limited knowledge of past variations in atmospheric H 2 levels. Here, we reconstruct atmospheric H 2 over the last 150 y using Antarctic firn air. We find a roughly 70% rise in atmospheric H 2 over the twentieth century that can be attributed to human activities. Surprisingly, there is no evidence that anthropogenic emissions of H 2 decreased during the late twentieth century due to reduced automotive emissions associated with air pollution controls. It is likely that nonautomotive anthropogenic H 2 emissions have been underestimated.