Measurement of Atmospheric He/N2 (Helium to Nitrogen) Ratio as a Tracer of Stratospheric-Tropospheric Exchange

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This project supports the development of new instrumentation to measure very precisely the ratio of the concentration of helium (He) to nitrogen (N2) in the atmosphere. Measurements of this ratio will be used to evaluate the exchange of atmospheric constituents between the stratosphere (the layer of the atmosphere just above the troposphere) and the troposphere, the lowest portion of the atmosphere closest to the Earth's surface. Better understanding of stratospheric-tropospheric exchange (STE) is important for increasing general knowledge about the atmosphere and improving models that predict weather and climate.The newly developed instrumentation will be used to: (1) measure long-term trends in He/N2 as recorded in the Scripps Institute of Oceanography archive of high pressure gas cylinders of air that extends back to the 1970s; (2) conduct real-time measurements of He/N2 for a period spanning one year at La Jolla, where stratospheric influences are expected in association with Santa Anna wind events; and (3) test new methods to allow He/N2 ratios to be measured in flask samples. Modeling studies will be used to assess the expected stratospheric influences on the He/N2 ratio. This project is expected to provide the first estimates of seasonal and synoptic variations in the He/N2 ratio. This effort will also improve the ability of Ar/N2 measurements to serve as a constraint on ocean warming. The new technique will be used to advance the understanding of stratospheric circulation and the resulting implications for tropospheric chemistry, and ultimately, by assessing the sources of these compounds, to attain a better understanding of the effects of human activities on the atmosphere.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.