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Project Status: complete

Report Published December 1995:

Title: Critical evaluation of a biogenic emission system for photochemical grid modeling in California.

Principal Investigator / Author(s): Winer, Arthur M

Contractor: UC Los Angeles

Contract Number: 93-725

Research Program Area: Atmospheric Processes

Topic Areas: Modeling, Natural (Biogenic) Sources


Assessing the relative effectiveness of VOC vs. NO, control, or simultaneous control of both precursors, in reducing photochemical smog in California's airsheds depends in part on obtaining accurate biogenic emissions inventories. However, while considerable progress has been made in quantifying the contribution of vegetation emissions of VOC many important uncertainties remain. In particular, the biogenic emission inventories prepared for key California airsheds may be based on inappropriate estimates for any or all of the following: biomass and biomass distribution, emission rate assignments, correction factors for diurnal and seasonal influences, and inaccurate coding or methodologies within available emissions models. The overall objective of this research was to critically and comprehensively evaluate the methodologies and databases with which biogenic hydrocarbon emission inventories are prepared for photochemical modeling in California's airsheds. The results included the following:

* A Critical Review of Biomass Databases
* A Critical Review and Update of Emission Rate Databases, Algorithms and Methodologies
* Assessment of the Utility of Remote Sensing and Aerial Imagery Technologies for Biomass Characterization
* A Critique of Current Vegetation Emission Inventory Models
* Identification of Gaps in Databases and Needed Research
* Recommendation of Valid Protocols for Assembling Biogenic Hydrocarbon Emission Inventories

Among the most important findings and recommendations were the following. There is a paucity of experimental data for leaf mass constants and other biomass metrics. Similarly, less than 25% of the relevant plant species in California have measured biogenic hydrocarbon emission rates and even when such data are available in almost all cases they represent only a single set of environmental and seasonal conditions. Additional measurements are needed and these can be made cost-effectively with guidance from taxonomic relationships. There is an important need to develop canopy correction factors more suitable for California's airsheds. Soil NO, measurements should be made in regions of high agricultural activity. Validation of biogenic emission inventories and model predictions should be attempted through appropriate ambient air measurements of biogenic hydrocarbons. Remote sensing is unlikely to lead to major advances in the near future in biomass characterization. A detailed evaluation of the four current biogenic emissions models suggests the use of BEIS-2, although GEMAP and VEGIES use input parameters that are more detailed and specific to California. Recommended procedures for assembling and verifying biogenic emissions estimates used in photochemical modeling are presented.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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