Science Inventory

EFFECTS OF USING THE CB05 VERSUS THE CB4 CHEMICAL MECHANISMS ON MODEL PREDICTIONS

Citation:

LUECKEN, D. J. AND G. SARWAR. EFFECTS OF USING THE CB05 VERSUS THE CB4 CHEMICAL MECHANISMS ON MODEL PREDICTIONS. Presented at 5th Annual CMAS Conference, Chapel Hill, NC, October 16 - 18, 2006.

Impact/Purpose:

The objective of this task is to improve EPA's ability to accurately predict the concentrations and deposition of air pollutants in the atmosphere that are known or suspected to cause cancer or other serious health effects to humans, or adverse environmental effects. It is an essential component of EPA's National Air Toxics Assessment (NATA), which seeks to identify and quantify the concentrations and sources of those hazardous air pollutants which are of greatest potential concern, in terms of contribution to population risk. It is a major contributor to NERL's Air Toxics Research Program.

"Air toxics" or "hazardous air pollutants" (HAPs) is a category that covers a large variety of chemicals, which range from relatively non reactive to extremely reactive; can exist in the gas, aqueous, and/or particle phases; display a large range of volatilities; experience varying deposition velocities, including in some cases revolatilization; and are emitted from a wide variety of sources at a large variety of different scales. In addition, concentrations of air toxics are needed by regulators for both short (days) as well as long (up to a year) time scales. These requirements challenge our current capabilities in air quality models far beyond the needs for other pollutants, such as ozone. The specific work being done under this task involves 1.) developing and testing chemical mechanisms which are appropriate for describing the chemistry of air toxics; 2.) incorporating these chemical and physical mechanisms into EPA's CMAQ modeling system and applying the model at a variety of scales; and 3.) developing the methods for using models to predict HAPs concentrations at subgrid or neighborhood scales; and 4.) using these tools to assess the magnitude and variability of concentrations to which urban populations are exposed.

Description:

The Carbon Bond 4 (CB4) chemical mechanism has been widely used for many years in box and air quality models to predict the effect of atmospheric chemistry on pollutant concentrations. Because of the importance of this mechanism and the length of time since its original development, the CB05 chemical mechanism was developed in 2005 and implemented in CMAQ release v4.5, and a final version is available in the 2006 CMAQ release (v4.6).

During 2006, concentration predictions by CMAQ using the CB05 chemical mechanism are being extensively compared with predictions using the older CB4 chemical mechanism, as well as with observational data. While some of the differences between the CB4 and the CB05 mechanisms are small, there are some significant differences in a few of the oxidant and particulate matter (PM) species, and the magnitude of these differences vary both temporally and spatially. In this study, we examine where and when the largest differences between the two mechanisms tend to occur.

Record Details:

Record Type:DOCUMENT( PRESENTATION/ EXTENDED ABSTRACT)
Product Published Date:10/16/2006
Record Last Revised:11/06/2006
Record ID: 159804