ARB Research Seminar

This page updated June 19, 2013

Evaluation of a Gas-Phase Atmospheric Reaction Mechanism for Low NOx Conditions

Photo of William P. L. Carter, Ph.D.

William P. L. Carter, Ph.D., University of California, Riverside

May 27, 2004
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


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 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.

Speaker Biography

Dr. William P. L. Carter holds a joint appointment at the Air Pollution Research Center and the College of Engineering Center for Environmental Research and Technology (CE-CERT) at UC Riverside. His research concerns the gas-phase atmospheric reactions of volatile organic compounds (VOCs) and the assessment of ozone and other impacts of VOCs in the atmosphere. This includes developing chemical mechanisms for airshed models, conducting environmental chamber experiments to evaluate and improve these mechanisms, and utilizing them in airshed models to develop ozone reactivity scales for VOCs. Ozone reactivity scales he developed have been incorporated into several VOC emissions regulations in California. Dr. Carter's current projects include utilizing a new environmental chamber facility for more comprehensive evaluation of gas-phase and particle formation mechanisms, evaluating impacts of selected coatings VOCs, updating and improving the SAPRC-99 mechanism, developing improved condensed mechanisms for models, and improving methods for incorporating speciation data into airshed models.

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