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Since the mid-1970s, ozone concentrations in California’s South Coast Air Basin (SoCAB) have been higher on weekends than on weekdays despite assumed lower emissions on weekends than on weekdays. The objective of the National Renewable Energy Laboratory (NREL) weekend effect project, performed by co-contractors Sonoma Technology, Inc.(STI) and the Desert Research Institute (DRI), is to conduct a study of the possible cause (s) of higher weekend ozone compared to weekday ozone in the SoCAB. In Phase I of this three-phase project, STI acquired emissions activity and meteorological data in order to establish data needs and priorities for Phase II field study data acquisition/measurements and worked with DRI to refine hypotheses for further testing in Phases II and III.

In this report, STI summarizes available emissions data. In order to identify existing sources of emissions activity data, literature reviews were conducted and discussions with several government agencies and industry experts were held. Significant effort was expended for on-road mobile sources since these are the single largest source of emissions in the SoCAB. During Phase II of the project, STI will compile data that can be used in Phase III to assess possible weekend effects. Data to be collected include traffic data on surface streets and freeways and patterns of emissions-related activities at commercial and residential locations near ambient monitors.