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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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Conventional Emissions Inventories: Maximizing Strengths and Minimizing Vulnerabilities
G. M. Hidy
Envair/Aerochem
The development of local and national emissions inventories in North America has followed a long established practice, largely designed in the early 1970s. NARSTO reviews in 2001 (ozone) and 2003 (PM) have noted that inventories serve a number of different purposes that require different levels of accuracy and precision in space and time. Applications address needs for source specific inventories used for permitting and regulatory compliance, urban and regional planning, industrial technology change, and air quality modeling. Inventories are based on a simple formula incorporating an emission factor, a process input rate, an activity pattern, and an emission control factor. The acquisition of these data for a large number of sources has proceeded over the years based on limited testing of single sources, and subsequent organization by local and national authorities. The inventories have been extended using emissions models to extrapolate inventory data in space and time for air quality assessments.
The emissions inventories prepared by Canada, Mexico and the United States generally have served a number of qualitative and semi-quantitative applications well for regulatory management processes. Nevertheless, the inventories (and the models) have long been known to have critical inaccuracies which have directly affected management decisions in a number of locations. Recently the requirements for quantification of emissions has reached a point where uncertainties for all categories, especially the large source categories, need to be defined or determined. This has placed substantial demands on the current system that have led investigators to seek a combination of innovative ways to verify the inventories using source measurements, air monitoring data, and air quality modeling techniques. These approaches vary in costs from “modest to very expensive”. To minimize the vulnerability to decision making, new, innovative practical approaches to emissions characterization are needed, that will complement the conventional inventories. The key to adopting a new portfolio of techniques emerging from the technical community will be the integration of the conventional practice with the new methods such that long term trends in emissions and human activities are documented.