Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder

Stephen A. Montzka

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-troposhere exchange; quantifying fluxes of trace gases from the United States; and effectively communicating scientific results to interested parties, nationally and internationally, including the public and policy makers.

Current Research

Interpreting observations from a multi-decadal sampling program for over 30 trace gases at 45 sites distributed throughout the global atmosphere is a continuing theme. Data obtained from measurements of these samples via high-precision gas chromatography coupled to mass spectrometry have been used recently for identifying an increase in emissions of CFC-11, an ozone-depleting substance banned by the Montreal Protocol in 2010. This renewed emission increase may suggest delays in ozone recovery as a result of a country or country not adhering to this international agreement. These data have also been used in recent studies for 1) investigating the influence on the ozone layer of increasing concentrations of short-lived gases not controlled by the Montreal Protocol (e.g., dichloromethane), 2) diagnosing the global and relative hemispheric concentration of the hydroxyl radical over time and estimating the impact of those changes on the global budget of methane, and 3) improving our understanding of regional and global budgets of carbonyl sulfide, which may enhance our understanding of CO2 uptake by terrestrial photosynthesis.

In addition to studying atmospheric changes on global scales, the U.S.-centric sampling program managed by the Carbon Cycle Group and NOAA has allowed investigations into national-scale issues. Data obtained from this regional network have been used to quantify national-scale emissions of ozone-depleting substances and non-CO2 greenhouse gases that show how the Montreal Protocol has substantially added to the reduction in U.S. total greenhouse gas emissions in recent years. These data have also been used to improve the quantification and attribution of atmospheric impacts associated with oil and gas exploration and development (including hydraulic fracturing) and enhance our understanding of continental-scale sources and sinks of carbonyl sulfide, a trace gas whose concentration changes over land to appear closely linked to terrestrial photosynthesis.

Recent Highlight

Emissions of CFC-11 graph

Emissions of CFC-11 derived from NOAA/CIRES global atmospheric measurements over time (black symbols and lines) compared to expected changes (dashed gray lines) given production magnitudes reported to the United Nations Environment Programme (green line).  The atmospheric data indicate a surprising increase in emissions of this ozone-depleting chemical in recent years.  This increase implies significant amounts of unreported production after 2010, the year when CFC-11 production was to have been phased-out globally.  Adapted from Figure 2 of Montzka et al. 2018, Nature 

Honors and Awards

  • 2018 Named a Fellow of the American Geophysical Union
  • 2016 Elected Member of the International Ozone Commission
  • 2016 Excellence in Refereeing Citation by GRL
  • 2015 Nominated into the Montreal Protocol's Who's Who
  • 2014 Colorado Governor's Award for High-Impact Research, Team Member
  • 2012 Excellence in Refereeing Citation by JGR-A
  • 2008 NOAA Administrator Award
  • 2008 U.S. Department of Commerce Silver Medal
  • 2007 Excellence in Refereeing Citation by GRL
  • 2007 U.S. EPA Stratospheric Ozone Protection Award
  • 2000 NOAA Research Employee of the Year
  • 1997 U.S. Department of Commerce Silver Medal
  • 1996-2009 Awarded NOAA Outstanding Scientific Paper of the Year Award (nine times)