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From the same journal

Analysis of long-term observations of NOx and CO in megacities and application to constraining emissions inventories

Research output: Contribution to journalArticle


  • Birgit Hassler
  • Brian C. McDonald
  • Gregory J. Frost
  • Agnes Borbon
  • David C. Carslaw
  • Kevin Civerolo
  • Claire Granier
  • Paul S. Monks
  • Sarah Monks
  • David D. Parrish
  • Ilana B. Pollack
  • Karen H. Rosenlof
  • Thomas B. Ryerson
  • Erika von Schneidemesser
  • Michael Trainer


Publication details

JournalGeophysical Research Letters
DateAccepted/In press - 29 Aug 2016
DateE-pub ahead of print - 22 Sep 2016
DatePublished (current) - 28 Sep 2016
Issue number18
Number of pages11
Pages (from-to)9920-9930
Early online date22/09/16
Original languageEnglish


Long-term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970–2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. cities demonstrates that motor vehicle emissions controls were largely responsible for U.S. urban NOx/CO trends in the past half century. Differing NOx/CO enhancement ratio trends in U.S. and European cities over the past 25 years highlights alternative strategies for mitigating transportation emissions, reflecting Europe's increased use of light-duty diesel vehicles and correspondingly slower decreases in NOx emissions compared to the U.S. A global inventory widely used by global chemistry models fails to capture these long-term trends and regional differences in U.S. and Europe megacity NOx/CO enhancement ratios, possibly contributing to these models' inability to accurately reproduce observed long-term changes in tropospheric ozone.

Bibliographical note

©2016. American Geophysical Union. All Rights Reserved. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

    Research areas

  • chemistry-climate models, emissions, inventories, long-term trends, megacities

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