Environmental Science and Engineering Seminar

The reported emissions of many anthropogenic greenhouse gases (GHGs) are inconsistent with their measured rates of increase in the atmosphere, most often showing that emissions are underreported.  Emissions of purely anthropogenic industrial GHGs, as distinct from those that also have natural biogenic sources, ought to be comparatively easy to quantify at their sources, but many of these gases show among the largest discrepancies with atmospheric measurements, and also have the largest global warming potentials (GWPs).  The Advanced Global Atmospheric Gases Experiment (AGAGE) has been studying these issues for a number of years and for a wide range of non-CO₂ GHGs, using real-time high frequency measurements and archived air samples.  Examples of large inconsistencies in global emissions include SF₆ and CF₄.  Based on high-frequency measurements of C₂F₆/CF₄ emission ratios using trajectory analysis in East Asia and Australia it is possible to separate and quantify the roles of the aluminum and semiconductor industries in contributing to the global increases of these two potent GHGs.  Measurements of HFC-23 (CHF₃), another very potent GHG, are used to locate and quantify its regional emissions through inverse modeling, and to show the role of the Clean Development Mechanism (CDM) in modulating its emissions.  And measurements of NF₃, a very potent GHG with rapidly growing uses in the electronics industry, show that despite very large initial discrepancies between reported and measured global emissions, industry can respond positively to such findings and effect major improvements in the percentage of NF₃ production that is emitted.  In the context of climate legislation, the solution to discrepancies between bottom-up and top-down emissions assessment lies in the use of improved optimal estimation methods and an expanded observational base to refine emission parameters globally and regionally.