Calpuff

CALPUFF CHEMISTRY UPGRADE

Prepared by
Prakash Karamchandani,
Shu-Yun Chen and Christian Seigneur

Atmospheric & Environmental Research, Inc.
2682 Bishop Drive, Suite 120
San Ramon, CA 94583

Prepared for
American Petroleum Institute
1220 L Street NW
Washington, DC 20005

Document CP277-07-01
February 2008

TABLE OF CONTENTS

Executive Summary...................................................................................... ES-1
1.

Introduction ...................................................................................................... 1-1

2.

Improvements to CALPUFF ............................................................................. 2-1
2.1 Improvements to Gas-phase Chemistry .................................................... 2-12.2 Improvements to Treatment of Inorganic PM ........................................... 2-3
2.3 Improvements to Treatment of Organic PM ............................................. 2-3
2.4 Implementation of Aqueous-phase Chemistry and Wet Removal ............. 2-6
2.5 User Guidance for New CALPUFF Chemistry Options............................ 2-8

3.

Model SimulationResults................................................................................. 3-1
3.1 Description of Simulations....................................................................... 3-1
3.2 Effect of Modifications in RIVAD/ARM3 Scheme .................................. 3-2
3.3 Effect of Improvements to Inorganic Aerosol Equilibrium Treatment .... 3-14
3.4 Effect of New Aqueous-Phase ChemistryTreatment.............................. 3-18
3.5 Effect of Improvements to Secondary Organic Aerosol Treatment ......... 3-21

4.

Sensitivity Studies ............................................................................................ 4-1
4.1 CALPUFF Sensitivity Studies ................................................................. 4-1
4.1.1 Effect of relativehumidity............................................................ 4-1
4.1.2 Effect of temperature.................................................................... 4-6
4.1.3 Effect of background NH3 concentration .................................... 4-11
4.2 Box-Model Sensitivity Studies............................................................... 4-11

5.

Conclusions and Recommendations.................................................................. 5-1

6.

References ........................................................................................................ 6-1

CALPUFF Chem istry Upgrade

i

EXECUTIVE SUMMARY
This report describes improvements made to CALPUFF, the preferred U.S. EPA model
for assessing long-range transport of air pollutants and their impacts onFederal Class I
areas under the Prevention of Significant Deterioration (PSD) program. These
improvements were made to the chemistry modules of CALPUFF to address some of the
shortcomings of the model.
The improvements to CALPUFF were tested using an existing plume chemistry database
for a large coal-fired power plant in central Tennessee. CALPUFF simulations were
conducted for three days inJuly 1999. Sensitivity studies with CALPUFF were
conducted to examine the effects of variations in relative humidity, temperature, and
background ammonia concentrations on model results. Box-model sensitivity studies
were also conducted to test the changes to the inorganic aerosol thermodynamic
equilibrium module.
The improvements made to CALPUFF include:


Correction of an error in theRIVAD gas-phase chemistry scheme treatment of
background ozone (O3), which can lead to an overestimation of the formation of
secondary particulate matter (PM) from the oxidation of primary species such as
sulfur dioxide (SO2) and nitrogen oxides (NOx). The error was due to a lack of
update of the O3 concentrations; it was corrected by saving a history of puff O3
concentrations so that the O3...