SLS Seminar: Michael McLellan (MIT)

Michael McLellan (MIT)
Wednesday, April 18, 2018 - 12:00pm to 1:00pm

Investigating Regional Nitrous Oxide Emissions using Isotopic Ratio Observations and a Bayesian Inverse Framework

Atmospheric nitrous oxide (N2O) significantly impacts Earth's climate due to its dual role as an inert potent greenhouse gas in the troposphere and as a reactive source of ozone-destroying nitrogen oxides in the stratosphere. However, the understanding of its total impact is incomplete as there remain significant uncertainties in the global budget of this gas. Due to unique heavy-atom (15N and 18O) isotopic substitutions made by different N2O sources and its stratospheric sink, the measurement of isotopic ratios in ambient air can help identify the distribution and magnitude of distinct sources. Estimation of N2O source and sink fluxes can be improved by combining isotopically resolved N2O observations with simulations using a chemical transport model including treatments of isotopic signatures of specific surface sources and stratospheric intrusions.

A temporally and spatially dense network of isotopically differentiated N2O observations could provide great advances in disentangling the effects of diverse source sectors on the global N2O budget. I will present the first high-frequency site-specific N2O isotopic composition data from the MIT Stheno-TILDAS continuous wave laser spectroscopy instrument at Mace Head, Ireland. The analysis of seasonal trends and shorter-term events in N2O isotopic ratios measured at Mace Head indicate the influence of emissions from isotopically different sources, as corroborated by contemporaneous correlative trace gas measurements made at Mace Head and by initial Lagrangian modeling results. Ongoing work that combines results from two atmospheric chemical transport models to help constrain source-specific European N2O emissions is also presented.

About the Series

The Atmosphere, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmosphere, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm in 54-915. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.