Download Gas Phase HAP Chemistry

Changes to the Chemical
Mechanisms for Hazardous Air
Pollutants in CMAQ version 4.6
W. T. Hutzell1, G. Pouliot2, and D. J. Luecken1
1Atmospheric
Modeling Division,
U. S. Environmental Protection Agency
2Atmospheric
Sciences Modeling Division,
Air Resources Laboratory, National Oceanic and Atmospheric
October 16, 2006
Background
• CMAQ version 4.5 has two different mechanisms
for Hazardous Air Pollutants (HAPs).
 CB4TX1P
 SAPRC99TX2P
• Each includes a specific type of HAPs.
 identified to produce large health risks over urban
areas
 treated because they can be simulated as gas phase
compounds.
• Each omits toxic components in Particulate
Matter (PM)
 Also linked to large risks to health over urban areas.
Background (cont.)
• Version 4.6 introduces two new mechanisms for
several HAPs.
• Each includes HAPs in CMAQ version 4.5.
• They also include more gas phase HAPs,
• As well as aerosol phase HAPs that represent
several toxic metals and diesel emissions.
• One mechanism, called SAPRC99TX3, builds
upon SAPRC99TX2P.
• The other, called CB05CLTX, adapts the
Carbon Bond 05 (CB05) mechanism.
Gas Phase HAPs
HAP
New HAPs in
CMAQ version 4.6
Acrylo nitrile
C arbon Tetrachloride
Propylene Dichloride
1,3-Dichlo ride Propene
1,1,2,2-Tetrachloride Ethane
Benzene
Chloroform
1,2-Dibromome thane
1,2-Dichlorome thane
Ethyle ne Oxide
Methylene Chloride
Perchloroethylene
Trichloroethylene
Vinyl Chloride
Naphthalene
Quino line
Hydrazine
2,4-Tolue ne Diisocyanate
Hexamethylene 1,6-Diisocyanate
Maleic Anhydride
Triethylamine
1,4-Dichlo robenzene
Total Formaldehyde
Total Acetaldehyde
To ta l Acrolein
1, 3-Butadiene
Formalde hyde Emissions Tracer
Acetalde hyde Emissions Tracer
Acrolein Emissions Tracer
CAS#
107-13-1
56-23-5
78-87-5
542-75-6
79-34-5
71-41-2
67-66-3
106-93-4
107-06-2
75-21-8
75-09-2
127-18-4
79-01-6
7501-4
91-20-3
91-22-5
302-01-2
584-84-9
822-06-0
108-31-6
121-44-8
106-46-7
50-00-0
75-07-0
107-02-8
106-99-0
50-00-0
75-07-0
107-02-8
Aerosol Phase HAPs
HAP
Beryllium Compounds
Nickel Compounds
Chromium (III) Compounds
Chromium (VI) Compounds
Lead Compounds
Manganese Compounds
Cadmium Compounds
Diesel Emissions Tracer
General Treatment in
Chemical Transport Model
• All HAPs undergo advection and diffusion.
• Wet deposition is determined by the HAP’s phase
 modal scavenging rate if aerosol phase
 the Henry's Law Constant if gas phase
• Dry deposition also depends on the HAP’s phase
 modal deposition velocity if aerosol phase
 nonzero deposition velocity if gas phase
• when screening implies dry deposition as important
Gas Phase HAP Chemistry
•Two methods calculate photochemical destruction and
production.
•First method adds species and reactions to O3 and radical
chemistry.
•HCHO, CH3CHO, 1,3-butadiene, acrolein and several
emission tracers
•reactions can affect numerical solution for O3 and radicals
•Second method estimates destruction based on O3 and radical
solution.
•calculation does not affect O3 and radicals
•Why use this approach?
•emissions are already accounted in lumped species
•low reactivity or emissions imply small effect on O3 and
radicals
Aerosol Phase HAP Processes
• They track emissions of toxic components within PM.
• Microphysical processing is similar to elemental carbon and
unidentified coarse mode PM.
 do not affect microphysical processes and deposition due
to their tracking function.
• They also do not affect cloud chemistry.
• Last point is not valid for two HAPs.
 “Cr(VI) + 3e-  Cr(III)” can occur via chemistry within
cloud droplets.
 Shortcoming is an avenue for model developers within
CMAS.
Simulation Details
• Domain covered the continental US and
spanned from surface to 100 mb.
• Horizontal grid size was 36X36 km2
• Emissions came form the combined 1999
NEI and Air Toxics database.
• Meteorology represented January and
July 2001 based on MM5 simulations.
Gas Phase Destruction Differences:
Summary, CB05CLTX – SAPRC99TX3
January 2001
ug/m^3, Beenzene SAPRC99TX3
ug/m^3, 1,3-Butadiene from SAPRC99TX3
July 2001
ug/m^3, Beenzene SAPRC99TX3
ug/m^3, 1,3-Butadiene from SAPRC99TX3
Gas Phase Destruction Differences:
Examples, CB05CLTX – SAPRC99TX3
1,3-Butadiene
Benzene
OH, 24 hour Averages:
CB05CLTX – SAPRC99TX3
January 2001
ppmV, Difference OH
ppmV, Difference OH
July 2001
ppmV, OH from SAPRC99TX3
ppmV, OH from SAPRC99TX3
ug/m^3, Difference Photochemical HCHO
January 2001
ug/m^3, Difference Photochemical CH3CHO
Gas Phase Production Differences:
Summary, CB05CLTX – SAPRC99TX3
ug/m^3, Difference Photochemical HCHO
July 2001
ug/m^3, Secondary CH3CHO from CB05CLTX
ug/m^3, Difference Photochemical CH3CHO
ug/m^3, Secondary HCHO from CB05CLTX
ug/m^3, Secondary HCHO from CB05CLTX
ug/m^3, Secondary CH3CHO from CB05CLTX
Gas Phase Production Differences:
Examples, CB05CLTX – SAPRC99TX3
Formaldehyde
Acetaldehyde
Aerosol Phase Differences:
ug/m^3, Difference Diesel Tracer Coarse Mode
January 2001
ng/m^3, Difference Cr(III) Accumulation Mode
Summary, CB05CLTX – SAPRC99TX3
ng/m^3, Difference Cr(III) Accumulation Mode
July 2001
ug/m^3, Diesel Tracer Coarse Mode from SAPRC99TX3
ug/m^3, Difference Diesel Tracer Coarse Mode
ng/m^3, Cr(III) Accumulation Mode from SAPRC99TX3
ng/m^3, Cr(III) Accumulation Mode from SAPRC99TX3
ug/m^3, Diesel Tracer Coarse Mode from SAPRC99TX3
Aerosol Differences:
Examples, CB05CLTX – SAPRC99TX3
Cr(III), Accumulation Mode
Diesel PM, Coarse Mode
What does CL in CB05CLTX mean?
• CB05CLTX contains additional species and reactions
not in SAPRC99TX3.
 Six species track emissions from anthropogenic and
biogenic sources (see version 4.6 release notes).
 Other species simulate the fate and transport of Cl2 and
HCl.
• Additional reactions represent how chlorine
compounds affect ozone.
 Reactions are based on Yarwood et al. (2005).
 We added the reaction, “HCl + OH  Cl.”
• NOTE, current mechanism settings omit Cl2 and HCl
emissions.
Closing Points
• New HAP mechanisms have not been evaluated
against observations.
• Each gives results consistent to the mechanisms
from that they were derived, i.e., CB05 or
SAPRC99.
• The new mechanisms then allow simultaneously
studying criteria and numerous toxic pollutants.
Disclaimer: The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency
(EPA) and U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number
DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and
approved for publication, it does not necessarily reflect their policies or views.