One of the more difficult inputs to characterize in a photochemical modeling study is the estimate of emissions from biogenic sources. There is considerable uncertainty in the emissions factors for individual plant species, as well as how to properly account for external variables that can effect the source strength of biogenic emitters. In general, the standard operating procedure in air quality modeling exercises has been to use a separate model to estimate emissions from these sources. In particular, the Biogenic Emissions Inventory System (BEIS) has been a frequently used tool to complete such assessments (Pierce, 1998). As the state-of-the-knowledge on biogenic emissions has progressed, several versions of the BEIS model have been released. The latest version of the BEIS model (BEIS-3) will be released in 2002. In an attempt to better understand the effects of these revised biogenic estimates on past, present, and future regulatory modeling applications, several air quality modeling simulations were completed for multiple domains and photochemical models.

Air quality simulations will be completed for three separate model configurations:

a) an Urban Airshed Model, version V (UAM-V) application over the eastern U.S. for a July 1995 episode,

b) a Community Multiscale Air Quality (CMAQ) model simulation for the same July 1995 eastern U.S. domain and episode, and

c) a CMAQ application for a western U.S. domain for a July 1996 episode.

Comparisons of model performance for ozone and fine particulates between the BEIS2 and BEIS3 base cases will be completed for each of these configurations. Additionally, it will be determined if either the control signal, control magnitude, or need for future controls could be significantly altered by the incorporation of the new biogenic emissions estimates. To the extent possible, the analyses will also attempt to determine which of the inputs to the biogenic models are particularly sensitive parameters.