This project will support the development of the first global emissions inventory for volcanic hydrogen sulfide (H2S). By improving estimates of natural sulfur emissions to the atmosphere, the uncertainty in the estimates of the global radiative forcing of anthropogenic sulfate aerosols will be reduced. The investigators of the project plan to: (1) make an initial inventory of global volcanic H2S emissions based on current carbon dioxide and sulfur dioxide emissions measured during passive degassing; (2) measure H2S emissions from select volcanoes; (3) use these observations along with previous work to construct a global emissions inventory of H2S from passive volcanic degassing; (4) implement the new volcanic H2S emissions inventory into the GEOS-Chem global chemical-transport model; and (5) examine the global chemical and radiative implications of the volcanic source of H2S. This work will partially support two graduate students, one each at the University of New Mexico and the University of Washington. 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.