Environmental Engineering Reference
In-Depth Information
2.8 Development and Application of the CMAQ Ozone
and Particle Precursor Tagging Methodologies
(OPTM and PPTM)
Sharon G. Douglas, Thomas C. Myers, Jay L. Haney, and Yihua Wei
ICF International, San Rafael, California, USA
1. Introduction
The Community Multiscale Air Quality (CMAQ) model is a state-of-the-science,
regional air quality modeling system that is designed to simulate the physical and
chemical processes that govern the formation, transport, and deposition of gaseous
and particulate species in the atmosphere. This paper describes the recent enhance-
ment of the CMAQ model to include source attribution capabilities for ozone and
particulate matter. The Ozone and Precursor Tagging Methodology (OPTM) and
the Particle and Precursor Tagging Methodology (PPTM) are designed to provide
detailed, quantitative information about the
contribution
of selected sources,
source categories, and/or source regions to simulated ozone and fine particulate
(PM
2.5
) concentrations, respectively. Emissions of precursor pollutants from selec-
ted sources, source categories, or source regions are (numerically) tagged and then
tracked throughout a simulation. The contribution from each tag to the resulting
simulated concentration of ozone, PM
2.5
, or any of the PM
2.5
component species
for any given location within the CMAQ modeling domain can be quantified.
2. Overview of OPTM and PPTM
The CMAQ simulation processes include advection, dispersion (or turbulent
mixing), chemical transformation, cloud processes, and wet and dry deposition.
Within the model, tagging is accomplished by the addition of duplicate model
species variables for each source, source category, or source region that is to be
tagged. For OPTM, the duplicated modeled species are ozone, oxides of nitrogen
(NO
x
), and volatile organic compounds (VOCs). For PPTM, the duplicated species
include all PM-related sulfur, nitrogen, and secondary organic compounds, as well
as primary organic carbon, elemental carbon, and other inorganic particulates. PPTM
can also be applied for mercury. The tagged species have the same properties and
are subjected to the ssameprocesses (e.g., advection, chemical transformation,
deposition) as the actual (or base) species. Because the tagged species are separate
from the base species, tagging does not alter or affect the base simulation results.
OPTM and PPTM have been implemented in versions 4.5, 4.6 and 4.7 of CMAQ.
