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

Changes to the Chemical Mechanisms for Hazardous Air Pollutants in CMAQ version 4.6

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 HAPsHAP CAS#

Acrylonitrile 107-13-1 Carbon Tetrachloride 56-23-5 Propylene Dichloride 78-87-5 1,3-Dichloride Propene 542-75-6 1,1,2,2-Tetrachloride Ethane 79-34-5 Benzene 71-41-2 Chloroform 67-66-3 1,2-Dibromomethane 106-93-4 1,2-Dichloromethane 107-06-2 Ethylene Oxide 75-21-8 Methylene Chloride 75-09-2 Perchloroethylene 127-18-4 Trichloroethylene 79-01-6 Vinyl Chloride 7501-4 Naphthalene 91-20-3 Quinoline 91-22-5 Hydrazine 302-01-2 2,4-Toluene Diisocyanate 584-84-9 Hexamethylene 1,6-Diisocyanate 822-06-0 Maleic Anhydride 108-31-6 Triethylamine 121-44-8 1,4-Dichlorobenzene 106-46-7 Total Formaldehyde 50-00-0 Total Acetaldehyde 75-07-0 Total Acrolein 107-02-8 1, 3-Butadiene 106-99-0 Formaldehyde Emissions Tracer 50-00-0 Acetaldehyde Emissions Tracer 75-07-0 Acrolein Emissions Tracer 107-02-8

New HAPs in CMAQ version

4.6

Aerosol Phase HAPsHAP

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

July 2001

ug/m^3, 1,3-Butadiene from SAPRC99TX3

ug/m^3, 1,3-Butadiene from SAPRC99TX3

ug/m^3, Beenzene SAPRC99TX3

ug/m^3, Beenzene SAPRC99TX3

Gas Phase Destruction Differences: Examples, CB05CLTX – SAPRC99TX3

1,3-Butadiene Benzene

OH, 24 hour Averages: CB05CLTX – SAPRC99TX3

July 2001 January 2001

ppmV, OH from SAPRC99TX3

ppm

V, D

iffer

ence

OH

ppmV, OH from SAPRC99TX3

ppm

V, D

iffer

ence

OH

Gas Phase Production Differences: Summary, CB05CLTX – SAPRC99TX3

January 2001

July 2001

ug/m

^3, D

iffer

ence

Pho

toch

emic

al H

CH

O

ug/m^3, Secondary CH3CHO from CB05CLTX

ug/m

^3, D

iffer

ence

Pho

toch

emic

al C

H3C

HO

ug/m

^3, D

iffer

ence

Pho

toch

emic

al C

H3C

HO

ug/m

^3, D

iffer

ence

Pho

toch

emic

al H

CH

O

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:Summary, CB05CLTX – SAPRC99TX3

January 2001

July 2001

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

ng/m

^3, D

iffer

ence

Cr(

III) A

ccum

ulat

ion

Mod

eng

/m^3

, Diff

eren

ce C

r(III

) Acc

umul

atio

n M

ode

ug/m

^3, D

iffer

ence

Die

sel T

race

r Coa

rse

Mod

eug

/m^3

, Diff

eren

ce D

iese

l Tra

cer C

oars

e M

ode

ug/m^3, Diesel Tracer Coarse Mode from SAPRC99TX3

Aerosol Differences: Examples, CB05CLTX – SAPRC99TX3Cr(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.