This report summarizes the efforts undertaken by Sonoma Technology, Inc. (STI) on behalf of the California Air Resources Board (ARB) to characterize, by day of week, activities associated with emissions of air pollutants. Activity data were collected in the South Coast Air Basin (SoCAB) during summer 2002. Activity data are an underlying component of emission inventories. In recent years, the ozone weekend effect, where ambient ozone concentrations tend to be higher on weekends than on weekdays in major urban areas, has been of particular interest.
A variety of tools were used to characterize day-of-week and time-of-day activity patterns for major types of emissions sources in the SoCAB: (1) telephone and mail surveys; (2) installation of global positioning systems (GPS) in volunteers' cars; (3) measurements of traffic volumes at fixed locations; (4) acquisition of continuous emissions monitoring systems (CEMS) data for major point sources of NOx; and (5) confirmation of emissions sources and activity patterns by in-neighborhood observers. The results show that activity levels generally decline on weekends (especially Sunday) relative to weekdays for (1) on-road mobile sources (about 10-25 percent with larger, 50-75 percent decreases for heavy-duty vehicles), (2) commercial off-road mobile sources (about 90-95 percent) and (3) commercial area sources (about 75-80 percent). In addition, NOx emissions from point sources declined about 5-10 percent on weekends. In contrast, activity levels for recreational sources (e.g., barbecues and recreational vehicles [boats, ATVs]) increased about 25-165 percent on weekends relative to weekdays. As observed in previous analyses, not only does the amount of vehicular activity change, but the timing also changes from a bimodal distribution associated with morning and afternoon commutes to work and school on workdays to a broad midday peak on weekends. New insights were gained from the instrumented light-duty-vehicle study: a high proportion, about 35 percent, of the highway vehicle miles traveled (VMT) occurred at speeds greater than 65 miles per hour and an apparent fewer number of trips per day were made than were counted in a previous study (about 2 less on both weekdays and weekends-4.7 vs. 6.7 on weekdays and 3.8 vs. 5.9 on weekends).
The results from this study can be used to refine summertime activity estimates and their associated emissions by time of day and day of week. Improved activity estimates will result in improved emission estimates and air quality modeling, which will help ensure that health-protective and cost-effective policies and plans are developed for controlling criteria pollutants and toxic air contaminants.
Lyle R. Chinkin is the Senior Vice President for Emissions, Policy, and Geographic Information Systems Services at Sonoma Technology, Inc. (STI). Those business areas encompass the preparation and assessment of stationary and mobile source emission inventories for use in air quality analyses and control strategy development. Mr. Chinkin is a nationally recognized expert in emission inventory preparation and assessment and air quality analyses. He has provided technical support to the U.S. Department of Justice Environmental Enforcement Division and has been appointed to the National research Council of the National Academy of Sciences Committee on the Effects of Changes in New Source Review Programs for Stationary Sources of Air Pollutants. He has performed numerous emission inventory and air quality studies primarily for government agencies. He also has directed analyses for industrial associations. His work involves emission inventory field measurements, surveys, development, improvement, preparation, and evaluation. He also serves as STI's corporate General Manager.
Ms. Dana Coe Sullivan is STI's Manager of Emissions Assessment. Ms. Sullivan has planned or coordinated several emissions studies, including a field study of ammonia emissions in California and development of gridded ammonia inventories for California, the Salt Lake City region, and the nine Midwestern states of the Central Regional Air Partnership (CENRAP). Some of Ms. Sullivan's other recent accomplishments include field studies and data analyses of weekday-weekend emissions activity patterns, development of emissions estimation guidance documents for northern California counties and the San Joaquin Valley, observational field surveys and analyses of PM emissions activities, and gridded emission inventories of offshore facilities in the Gulf of Mexico. In addition, Ms. Sullivan has been responsible for designing the algorithms that underpin two emission estimation software tools for the petroleum production industry. Currently, Ms. Sullivan is working on the development of emission inventories for the CENRAP, including inventories of agricultural and prescribed burning activities, on-road mobile sources, off-road mobile sources, and agricultural dust.
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