A Global Survey of Helium in the Troposphere: Advancing the Application of Helium as a Tracer of Natural Gas Usage and Stratosphere-Troposphere Exchange

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This project seeks to conduct a global survey of the noble gas helium building upon a previously developed measurement technique. Helium, which is a difficult gas to measure, can be used as an atmospheric tracer, meaning that new measurements could help us better understand a wide range of processes including large-scale atmospheric transport between the northern and southern hemispheres as well as small-scale processes that emit helium such natural gas extraction. The unique measurements of helium to be collected in this project will provide new insight into a variety of atmospheric transport phenomena and will increase our understanding of the sources and variability of helium and potentially other noble gases. Early career scientists and a graduate student will be supported throughout the course of this project, and the data collected will be shared with the wider scientific community.The new observations to be made during this project will be of the ratio between the gases helium (He) and nitrogen (N2) (He/N2) via a new mass spectrometric measurement technique using a dual-trapping system and cryo-enrichment inlets developed under a previous NSF-funded project. There are four research questions being asked in this proposed work: (1) what is the interannual variability of the most abundant helium isotope 4He?; (2) what are the He/N2 spatial gradients, particularly between the northern and southern hemispheres?; (3) what is the magnitude of seasonal He/N2 variations?; and (4) what can be learned by examining high frequency He variability? This proposed work will use three sources of measurement: historic flask samples collected from previous work that has demonstrated an increasing trend in atmospheric He levels over the last 50 years, the ongoing collection of flask samples collected routinely by the Scripps oxygen program, which is a network of 10 surface flask stations spread out around the Pacific Ocean capable of resolving global-scale signals, and quasi-continuous ambient samples taken at the Scripps Pier in La Jolla, California.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.