Project at a Glance

Title: Evaluation of a gas-phase atmospheric reaction mechanism for low NOx conditions.

Principal Investigator / Author(s): Carter, William P. L

Contractor: UC Riverside

Contract Number: 01-305

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity


The ability SAPRC-99 atmospheric chemical mechanism to predict photochemical smog formation under low NOx conditions was evaluated by comparing model predictions to results experiments from three different environmental chamber facilities. These included new experiments from our UCR EPA environmental chamber, and previous experiments at from the Tennessee Valley Authority (TVA) and the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) chambers. The facility and procedures for the new UCR EPA experiments, and the procedures for modeling data from all three chambers, are discussed. The results indicated no apparent low NOx mechanism performance problem for SAPRC-99 for simple chemical systems and for ambient surrogate reactive organic gas (ROG) - NOx experiments with ROG/NOx ratios high enough for maximum ozone formation potentials to be achieved. However, a consistent underprediction bias for NO oxidation and O3 formation rates was found in simulations ambient surrogate ROG - NOx experiments at low ROG/NOx ratios. The widely used Carbon Bond 4 mechanism was even worse in this regard. Furthermore, new aromatic - CO - NOx experiments indicate problems with current aromatic mechanisms that may be the cause of the low ROG/NOx underpredictions. Integrated reaction rate calculations indicate that increasing the accuracy in representing combination reactions of organic peroxy radicals will probably have an insignificant effect on model predictions. It is concluded that at a minimum new aromatic mechanisms need to be developed for model predictions to be consistent with available data.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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