Sensitivity-Based VOC Reactivity Calculation

Abstract

Volatile Organic Compound (VOC) reactivity scales are used to compare the ozone-forming potentials of various compounds. The comparison allows for substitution of compounds to lessen formation of ozone from paints, solvents, and other products. Current reactivity scales for VOC compounds were first developed using 1-D trajectory/box models for short pollution episodes several decades ago. In this study, they are updated using the 3-D air quality model CMAQ instrumented with DDM-3D. DDM-3D sensitivities are used to update relative reactivity metrics of a number of VOCs over more meaningful timescales. Using sensitivity calculation in the context of an air quality model for reactivity calculations avoids the issues of trajectory assumptions inherent in the 1-D calculations and allow for calculation of regional representative metrics.

Questions and Answers

Questioner: S. Arunachalam

Question: You mentioned lower formaldehyde reactivity calculated with ddm-based model compared to box-model. Why? What is the mechanism that causes this difference?

Answer: Formaldehyde and other aldehydes are more reactive in box model (resulting in higher reactivity quantifications), because the residence time considered doesn’t allow for carryover of products that continue to be chemically active in the CTM.

Questioner: A. Hakami

Question: How did you prepare your individual VOC emissions?

Answer: VOC emissions for the sensitivity calculations where set to 0.0001 mol/s for each species constant over the entire domain. This was a quantity sufficiently small compared to total VOC emissions to not impact base model ozone concentrations.