Stephen Montzka
GML Senior Scientist
Mailing Address:
NOAA Global Monitoring Laboratory
325 Broadway R/GML
Boulder CO 80305-3328
Phone: 720-295-9701
Email: stephen.a.montzka@noaa.gov
Research Interests:
Measuring and understanding changes in the chemical composition of the global atmosphere, particularly related to ozone-depleting substances, greenhouse gases, and hazardous air pollutants; identifying the role of natural and human-related influences on hemispheric to global-scale atmospheric composition; diagnosing variability in the atmosphere's oxidizing capacity, in terrestrial photosynthesis, and in stratosphere-troposphere exchange; quantifying fluxes of trace gases from the United States as a whole and on the scale of individual States; and effectively communicating scientific results to interested parties, nationally and internationally, including the public and policy makers.
Current Research
My research primarily involves making and interpreting trace gas atmospheric concentration measurements over multiple decades of over 30 trace gases at 45 sites distributed throughout the globe. The measurements are obtained from high-precision gas chromatography-mass spectrometric methods and most recently enabled the discovery of an apparent violation of the most successful international environmental agreement to date, the Montreal Protocol on Substances that Deplete the Ozone Layer. The unexpected increase in global emissions of CFC-11, an ozone-depleting substance banned by the Montreal Protocol in 2010, appears to have abated following this discovery in 2018. Measurements of other trace gases obtained from this program have also been used in recent studies for 1) quantifying emissions of other potent greenhouse gases and ozone-depleting substances on global scales and also regionally across the United States; 2) investigating sources and quantifying impacts of short-lived chlorine- and bromine-containing gases arising from natural processes and human activities (e.g., dichloromethane) but that are not controlled by the Montreal Protocol; 3) diagnosing the global and relative hemispheric concentration of the hydroxyl radical and estimating the impact of those changes on the global budget of methane; and 4) improving our understanding of regional and global budgets of carbonyl sulfide, which may enhance our understanding of carbon dioxide uptake by terrestrial photosynthesis.