Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published February 1993 | public
Journal Article

Photochemical modeling of the Southern California air quality study


The Southern California Air Quality Study (SCAQS) provides detailed experimental observations that can be used to explore the causes of the Los Angeles smog problem. In the present study, the CIT photochemical airshed model is updated and then applied to the August 27-29, 1987, SCAQS intensive monitoring period. Using measured meteorological parameters, measured initial and boundary conditions, and the official emission inventory prepared by the government, ozone concentrations are underpredicted by 23% on average. Recent field experiments suggest that emissions of organic gases and carbon monoxide are understated in the official emission inventory. When the organic gas emissions from on-road vehicle engine exhaust are increased as suggested by emission rate measurements made in a Los Angeles area roadway tunnel during SCAQS, ozone predictions match the observed concentrations more closely (the mean normalized bias in ozone predictions for this case is +1%). Reactive hydrocarbon concentrations are underpredicted by 35% in the base case calculation, but are underpredicted by only 12% in the increased emission case. Results of this study thus support prior estimates that the organic gas emissions in Los Angeles have been understated in recent years.

Additional Information

© 1993 American Chemical Society. Received for review June 1, 1992. Revised manuscript received October 15, 1992. Accepted October 26, 1992. This study was sponsored by the Coordinating Research Council (CRC) under Project SCAQS-8. We gratefully acknowledge the assistance of Bart Croes and Paul Allen of the California Air Resources Board in supplying SCAQS-related data. We also thank Dr. Julia Lester of the South Coast Air Quality Management District for providing biogenic emission data. We thank all of the CRC reviewers for their numerous helpful comments.

Additional details

August 20, 2023
October 19, 2023