US EPA

11831401 

Technical Report 

Implementation of the SAPRC-99 chemical mechanism into the Models-3 framework 

Carter, WPL 

2000 

California Air Resources Board (CARB) 

Sacramento, CA 

106 

English 

This report documents the files, software and procedures needed to implement the SAPRC-99 detailed chemical mechanism into the Models-3 software framework. The SAPRC-99 mechanism is a detailed mechanism for the gas-phase atmospheric reactions of volatile organic compounds (VOCs) and oxides of nitrogen (NOx) in urban and regional atmospheres, and represents the state-of-the-art as of mid-
1999. It is a completely updated and expanded version of the earlier SAPRC mechanisms, and is comprehensively documented in a report to the California Air Resources Board (Carter, 1999). It has the
capability of separately representing the atmospheric reactions of ~400 types of VOCs, and can be used to estimate reactivities for ~550 VOC categories. Condensed versions of this mechanism have been
developed for use in regional models, using a more limited number of lumped VOC classes whose mechanistic parameters depend on the mixture of compounds they represent. Different versions can be
used depending on which VOC mixture is used to derive the mechanisms and parameters for these lumped VOC classes. This report describes the implementation of two condensed versions of SAPRC-99 into the Models-3 framework, one where the lumped VOC classes are derived from VOCs measured in ambient air, and one where the lumped VOC classes are derived from VOCs present in a recent EPA emissions inventory. Methods for deriving versions of the mechanism representing other mixtures or emissions inventories, and for explicitly representing selected VOCs for reactivity assessment and other purposes, are discussed. The procedures for obtaining, installing, and using the software and files needed to implement this mechanism are described.