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

Distinguished Lecture Series: Dr. Paul Wennberg

Title: “Improving Air Quality: Is less NOx always better?”

Abstract: Regulations aimed at improving air quality in urban areas like Los Angeles have made rapid progress on reducing nitric oxide and hydrocarbon emissions. As old cars have been taken off the street in favor of cleaner new cars and diesel trucks have been retrofitted or replaced, nitric oxide emissions have dropped rapidly. During the last decade, for example, the amount of nitric oxide in Los Angeles's air has dropped by half. Air pollution regulations have also led to reductions in hydrocarbon emissions, but unlike NOx, these decreases are slowing. Hydrocarbons come from a variety of sources, making control strategies more challenging. For example, these compounds are released by the two-cycle engines used in leaf blowers and lawn mowers -- equipment that tends to stay in service longer than cars and is subject to fewer regulations. Thus, we are now entering a phase where declining NOx emissions are not matched by declining hydrocarbon emissions – a phase with little precedent. With respect to ozone levels, there is now significant evidence that we are headed the wrong way in Los Angeles. Improvements in aerosol burden have also slowed. Some of this has been predicted by standard air quality models, but emerging research described here suggests that air quality in a low-NOx / high hydrocarbon world may be worse than anticipated.

Bio: Paul Wennberg is the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Engineering at the California Institute of Technology. He also serves as Director of The Linde Center for Global Environmental Science. He joined Caltech in 1998 after receiving a B.A. from Oberlin College and a Ph.D. from Harvard (both in Chemistry). His research focuses on atmospheric composition. To study the long lived greenhouse gases, he is the Chair of the Total Carbon Column Observing Network and a science team member of the Orbiting Carbon Observatory mission (OCO-2). For air quality, his research group has invented new methods for quantifying gas-phase organic oxidation products in the atmosphere and participates in NASA and NSF funded field activities designed to improve our understanding of air quality and climate.


Friday, February 16, 2018





  • CIRES employees
  • CU Boulder employees
  • General Public
  • NOAA employees
  • Science collaborators


  • DLS
  • Open to Public



CIRES Auditorium, Room 338