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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Weekday-weekend Emissions Patterns in Southern California: Observations and Implications
Dana Coe, Lyle Chinkin, Tami Funk, Courtney Gorin, Stephen Reid, and Patricia Stiefer
Sonoma Technology, Inc., Petaluma, California 94954
Over the past ten years, average peak ozone concentrations in Los Angeles were as much as 55% higher on weekends than on weekdays (under comparable meteorological conditions), even though weekend ozone precursor emissions are low relative to weekday emissions. Over the past three years, Sonoma Technology, Inc., (STI) has conducted several measurement programs to study weekday-weekend (WDWE) activity patterns for sources of ozone precursor emissions. The objectives were (1) to formulate improved diurnal and weekly emissions activity profiles, which are used as inputs to air quality models, for several source categories; and (2) to contribute (in conjunction with other concurrent research efforts) to the general understanding of weekday-to-weekend variability in air quality, which has been noted in Los Angeles and other urban areas. STI´s measurement programs encompassed an array of emissions source categories: on-road mobile, off-road mobile, major point, residential area, and commercial area sources. A variety of measurement techniques were used. Data were collected by monitoring traffic volumes on surface streets, by surveying residents and businesses by telephone and mail, by monitoring individual volunteers´ travel activity patterns with the use of in-vehicle instruments (i.e., global positioning system receivers with data loggers), by acquiring freeway-based traffic volume data, and by acquiring data from the continuous emissions monitoring systems (CEMS) of major stationary point sources. This paper will present a synthesized overview of STI´s methods and findings with the findings of other researchers. In addition, this paper will include a discussion of the implications of these findings with respect to weekday-to-weekend differences in emissions and ozone air quality in the South Coast Air Basin of southern California. In summary, it will be shown that:
1) WD-WE variabilities in activity patterns have quantifiable impacts on ROG and NO emissions in Los Angeles.
2) When these quantifiable impacts are used to adjust the emission inventory of southern California, it appears that weekend emissions patterns favor ozone formation in Los Angeles to a greater extent than do weekday emission patterns.
3) This phenomenon is due to increased ROG:NO ratios toward a more efficient ozone production x regime and a reduced morning titration capacity of ozone by NOx.