Evaluation of Dispersion Models for Particulate Matter

Focus Area

Air Quality


Air Quality






2-3 years

Research Idea Scope

In 2012, the EPA MOVES
model became a requirement for air emissions modeling on transportation
projects.  In addition to MOVES, EPA
regulations require dispersion modeling using one of two allowable dispersion
models for analyzing particulate matter: AERMOD and CAL3QHCR.  The challenge faced by state DOTs is that the
two dispersion models produce different results.  Related research is conflicting about which
model is more accurate and appropriate for various project conditions.  This uncertainty poses risks to state DOTs
(e.g., increased project schedule and budget) and opens the door to legal


To address these challenges, research is needed to:


* Evaluate the performance of regulatory air quality dispersion
models (AERMOD and CAL3QHCR) compared to measured data for particulate matter
for typical highway, intermodal and transit project types.

* Identify, obtain and quality assure data as needed for this
purpose, including near-road monitoring, meteorological, traffic and other

* Determine the most critical input data to improve accuracy and
reduce uncertainty, based on the results of the model evaluation.


Involve key stakeholders in the study as appropriate, including
the US EPA, US DOT, state DOTs, experts from the academic community, and others
as may be determined in the study.


The final report will:

* Document the accuracy and level of uncertainty for each
dispersion model

* Recommend the appropriate model and critical inputs for each
project type

* Outline potential model improvement areas

* Provide options for consideration for future updates to the EPA
Guideline on Air Quality Models (Appendix W of 40 CFR Part 51)


Background: This topic area was also suggested at the 2012 TRB
meeting of the Transportation and Air Quality Committee (ADC20) Project-Level
Analysis Subcommittee and included in suggestions for best practices for model
improvement programs in the 2012 annual SCOE meeting and 2013 TRB ADC20
Project-Level Analysis Subcommittee meetings.


Topic area supported by:

* Tim Sexton, Chair, AASHTO SCOE, Chair, Air Quality, Energy and
Climate Change Subcommittee

* Jackie Ploch, AASHTO SCOE, Vice-Chair,  Air Quality, Energy and Climate Change

* Christopher Voigt, AASHTO SCOE Research Task Force, Air Quality,
Energy and Climate Change Subcommittee Representative

Urgency and Payoff

Both models are currently being used by state DOTs depending on user preference,
understanding of current EPA guidance, and/or project conditions.  State DOTs and other project sponsors have an urgent need to know which model (AERMOD and CAL3QHCR) is the most accurate,
appropriate, and cost-effective for various project scenarios.  If certain project conditions result in
significant differences between modeled results, there could be technical,
procedural, and legal implications.

Suggested By

Christopher Voigt, Virginia DOT

[email protected]