Environmental Engineering Reference
In-Depth Information
2.14 A Comparison of Multiple Ozone and Particulate
Matter Source Apportionment Models
Kirk Baker and Brian Timin
U.S. Environmental Protection Agency
1. Introduction
It is useful to understand what types of sources or regions are contributing to
ozone estimated by photochemical grid models. Understanding the contribution
from particular sources to specific geographic receptor locations helps regulators
develop effective emissions control strategies. Source apportionment is an alter-
native approach to zero-out modeling and has the advantage of being much more
efficient with computational resources. The incremental run-time associated with
the additional source region tracking is far less than performing numerous iterative
zero-out simulations.
Ozone source apportionment tracks the contribution to model ozone estimates
from pre-cursor emissions of nitrogen oxides (NOX) and volatile organic com-
pounds (VOC). Particulate source apportionment tracks contributions to particulate
species from pre-cursor emissions. Ozone and particulate source apportionment
are implemented in state of the science photochemical grid models CMAQ and
CAMx.
The Milwaukee metropolitan area was chosen for an exercise comparing absolute
model predictions and source contribution estimates using CAMx and CMAQ
source apportionment. The source apportionment estimates are compared for 11
specific geographic tags, all other sources that were not tagged, and boundary
conditions at monitors located in Milwaukee and Waukesha counties in Wisconsin.
The 11 tags constitute the emissions from all source sectors in entire counties or
groups of counties.
2. Methods
Each model was applied with particulate source apportionment to a modeling
domain covering the Midwest United States with 12 km sized grid cells over 4
months in 2002: January, April, July, and October. Ozone source apportionment is
only applied for the month of July 2002. The SMOKE emissions model was run
separately for each source region to ensure that each geographic region tag only
contains emissions for that specific area. Ozone source apportionment in CAMx
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