Research Projects

Project at a Glance

Project Status: complete

Title: Analysis of historical ozone trends in Los Angeles sorted by the NMHC/NOx ratio.

Principal Investigator / Author(s): Trijonis, John

Contractor: Santa Fe Research Corporation

Contract Number: A1-056-32

Research Program Area: Atmospheric Processes


The EPA EKMA ozone model suggests that the Los Angeles atmosphere is currently in a condition, with respect to the ambient NMHC / NOx ratio, where ozone levels should be extremely sensitive to future reductions in hydrocarbon emissions. A method is devised to test this hypothesis by investigating historical ozone trends grouped according to percentiles in the daily 6:00 a.m. - 9:00 a.m. NMHC / NOx ratio. In essence, the days of lowest NMHC / NOx, ratio in the middle 1960s are used to represent current conditions, and future hydrocarbon reductions are simulated by examining the effect of historical control strategies on the low ratio days.

The method is applied to two ozone receptor sites, Azusa and Downtown Los Angeles, using historical trend data from 1964 to 1978. Special attention is paid to choosing or determining the best ozone air quality indices, source / receptor transport restrictions, historical precursor trends, and EKMA modeling parameters. The historical trend data do not confirm the EKMA hypothesis; contrary to EKMA predictions, historical ozone trends are nearly identical on low, medium, and high ratio days. This finding is inconclusive in the sense that we cannot be sure whether the EKMA hypothesis is erroneous or whether the study has been undermined by errors in the data base (e.g. in the routine data for the ambient NMHC / NOx ratio).


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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