Weekend/weekday Ozone Observations in the South Coast Air Basin: Volume I – Executive Summary

(STI) conducted a study of the causes of elevated ozone levels on weekends in the South Coast (Los Angeles) Air Basin (SoCAB). This work was conducted over a period of 30 months beginning in December 1999. In the initial phase of the study, DRI examined the spatial, temporal, and statistical distributions of ozone, carbon monoxide, total non-methane hydrocarbons, and nitrogen oxides for routine monitoring sites in the SoCAB with continuous data from 1981 to 1998. STI reviewed available activity data for VOC and NOx emissions and investigated important meteorological phenomena in the SoCAB in the context of day-of-week variations. The results and findings from these retrospective analyses are summarized in the following three volumes: In the second phase of the study, a field measurement program was conducted in September-October 2000 to collect and assemble air quality and emission activity databases to examine relationships between emission patterns and key air quality parameters relevant to the weekend ozone effect. The following interim report presents preliminary results from the field study and describes the applicable measurement methods and approaches for data analysis: The final report of this study consists of the three volumes referenced below. The Executive Summary (Volume I) provides a synthesis of the results obtained by DRI and STI with respect to a variety of hypotheses for the weekend ozone effect. Volume II documents the results ii obtained by DRI from the Phase II field study. It also summarizes the retrospective analyses performed during Phase I and additional analyses that were conducted by DRI to update the findings from Phase I. Volume III is a summary of STI's analysis of the prevailing meteorology during the Phase II field study and their collection of emission activity data in support of this study. Volume III also includes a discussion of weekday/weekend differences in hydrocarbon emissions and ambient concentrations. We gratefully acknowledge the administrative and technical support provide by Dr. Douglas Lawson of NREL and Mr. Brent Bailey of the CRC. We thank the South Coast Air Quality Management District for access to the Azusa and Pico Rivera monitoring stations and for operating their continuous gas chromatograph at the Pico Rivera PAMS site during the study. We also thank the California Air Resources Board for collecting hydrocarbon speciation data at Los Angeles – North Main. We also gratefully acknowledge the Bay Area Air Quality Management District for use of their monitoring van and the …