Photochemical aging of volatile organic compounds in the Los Angeles basin: Weekday-weekend effect

Carsten Warneke, Joost A. De Gouw, Peter M. Edwards, John S. Holloway, Jessica B. Gilman, William C. Kuster, Martin Graus, Elliot Atlas, Don Blake, Drew R. Gentner, Allen H. Goldstein, Robert A. Harley, Sergio Alvarez, Bernhard Rappenglueck, Michael Trainer, David D. Parrish

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


During the CalNex (California Research at the Nexus of Air Quality and Climate Change) field study in May-June 2010, measurements of volatile organic compounds (VOCs) were performed in the Los Angeles (LA) basin onboard a NOAA research aircraft and at a ground site located in Pasadena. A weekday-weekend effect in ozone, caused by lower NOx emissions due to reduced diesel truck traffic in the weekends, has been previously observed in Los Angeles and other cities. Measurements in the Caldecott tunnel show that emission ratios of VOCs do not vary with the day of the week, but measurements during CalNex2010 show a VOC weekday-weekend effect through faster photochemical processing at lower ambient NOx mixing ratios. Ambient VOC enhancement ratios of long-lived species such as benzene are the same between weekdays and weekends, whereas enhancement ratios of short-lived species, such as trimethyl benzene, are up to a factor of three lower on weekends. Based upon the observed differences in VOC enhancement ratios to CO, we determine that photochemical processing was on average 65%-75% faster on weekends during CalNex2010, which indicates that ambient OH radical concentrations were larger by this factor causing the observed change in VOC composition. A box model calculation based on the Master Chemical Mechanism was used to verify the increase in photochemical processing in the weekends. Key PointsSpatial and temporal photochemical processing in Los AngelesVOC weekday-weekend effectFaster photochemistry in weekends

Original languageEnglish (US)
Pages (from-to)5018-5028
Number of pages11
JournalJournal of Geophysical Research: Atmospheres
Issue number10
StatePublished - May 27 2013


  • Faster photochemistry in weekends
  • Spatial and temporal photochemical processing in Los Angeles
  • VOC weekday-weekend effect

ASJC Scopus subject areas

  • Atmospheric Science
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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