Implementation and application of sub-grid-scale plume treatment in the latest version of EPA’s third-generation air quality model, CMAQ 5.01

Abstract

The Community Multiscale Air Quality (CMAQ) modeling system Version 5.0 (CMAQv5.0) was released by the U.S. Environmental Protection Agency (EPA) in February 2012, with an interim release (v5.01) in July 2012. Because CMAQ is a community model, the EPA encourages the development of proven alternative science treatments by external scientists and developers that can be incorporated as part of an official CMAQ release. This paper describes the implementation, evaluation, and testing of a plume-in-grid (PinG) module in CMAQ 5.01. The PinG module, also referred to as Advanced Plume Treatment (APT), provides the capability of resolving sub-grid-scale processes, such as the transport and chemistry of point-source plumes, in a grid model. The new PinG module in CMAQ 5.01 is applied and evaluated for two 15-day summer and winter periods in 2005 to the eastern United States, and the results are compared with those from the base CMAQ 5.01. Eighteen large point sources of NOx in the eastern United States were selected for explicit plume treatment with APT in the PinG simulation. The results show that overall model performance is negligibly affected when PinG treatment is included. However, the PinG model predicts significantly different contributions of the 18 sources to pollutant concentrations and deposition downwind of the point sources compared to the base model.

Implications: 

This study describes the incorporation of a plume-in-grid (PinG) capability within the latest version of the EPA grid model, CMAQ. The capability addresses the inherent limitation of the grid model to resolve processes, such as the evolution of point-source plumes, which occur at scales much smaller than the grid resolution. The base grid model and the PinG version predict different source contributions to ozone and PM_2.5 concentrations that need to be considered when source attribution studies are conducted to determine the impacts of large point sources on downwind concentrations and deposition of primary and secondary pollutants.

Acknowledgments

The authors gratefully acknowledge the early access provided by the EPA to the beta version of CMAQ 5, and the several useful discussions with EPA scientists from the Atmospheric Modeling and Analysis Division throughout the course of the study. The authors are also grateful to the anonymous reviewers for their valuable suggestions on improving the paper.

Additional information

Notes on contributors

Prakash Karamchandani

Prakash Karamchandani is a senior manager, Jeremiah Johnson is a senior associate, and Greg Yarwood is a principal at ENVIRON International, Novato, CA.

Jeremiah Johnson

Prakash Karamchandani is a senior manager, Jeremiah Johnson is a senior associate, and Greg Yarwood is a principal at ENVIRON International, Novato, CA.

Greg Yarwood

Prakash Karamchandani is a senior manager, Jeremiah Johnson is a senior associate, and Greg Yarwood is a principal at ENVIRON International, Novato, CA.

Eladio Knipping

Eladio Knipping is a senior technical manager at Electric Power Research Institute (EPRI).