Title: William T. Hutzell, Shawn J. Roselle, Annmarie G. Carlton, and O. Russell Bullock
1Changes to the Multi-Pollutant version in the
CMAQ 4.7
- William T. Hutzell, Shawn J. Roselle, Annmarie G.
Carlton, and O. Russell Bullock - Atmospheric Modeling Division
- US EPA
2Background Multi-Pollutant Model
- Developed to simulate criteria and hazardous air
pollutants in a single modeling study - examine co-benefits of emission reductions over
multiple interest - O3, Particulate Matter, and Hazardous Air
Pollutants (HAPs) - Roselle et al. (2007) presented a prototype of
the Multi-Pollutant Model - mechanism called CB05TXHG_AE4_AQ
- Based on CB05 mechanisms for mercury and other
HAPs in CMAQ version 4.6
3Multi-Pollutant Model in version 4.7
- Updates prototype in Roselle et al (2007)
- photochemical production of Secondary Organic
Aerosols (SOA) - aerosol physics for SOA and interactive coarse
mode - cloud chemistry of organic compounds and SOA
- In-calculations for dry deposition and emission
processes - New mechanism called CB05TXHG_AE5_AQ
- Specific settings needed to build and run the
Multi-Pollutant model. - Consult release notes on building and running the
model.
4Goals of this Presentation
- Describe major changes to new science options for
Multi-Pollutant Model - Present differences in predictions from CMAQ
using CB05CL_AE5_AQ, the standard version - Highlight differences in predictions from the
prototype of the Multi-Pollutant Model
5Gas Chemistry
- Adds to CB05CL_AE5_AQ the species and reactions
for Hg compounds and other HAPs from
CB05HG_AE4_AQ and CB05CLTX_AE4_AQ - Two methods compute the chemical transformation
of gas phase Hg and other HAPs - One participates in ozone and radical
photochemistry - Other does not affect ozone and radical
concentrations and serves as reactive tracers. - Changes from CB05TXHG_AE4_AQ
- adds a new reaction, HG CL ? HGIIGAS
- This reaction should produce Hg(I)
- HGIIGAS redefined as reactive gaseous mercury
- i.e., Hg(I) Hg(II).
- Hg(I) assumed to quickly convert into Hg(II)
- the oxidation process not explicitly represented
6Aerosols
- Adds aerosol species representing mercury and
other toxic metals - They do not affect aerosol microphysics and
deposition rates - These aerosols species do coagulate and mode
merge - Mercury species differ from the other metallic
aerosols - photochemical source of particulate mercury
- goes directly into the accumulation mode
- assumes accumulation mode dominates condensation
onto the three aerosol modes - unlike version 4.6 where fine modes divided
condensation based on their surface area
7In-Cloud Chemistry
- Adds in-scavenging for mercury and other metallic
aerosols. - Adds cloud chemistry for atmospheric mercury
- Based on Bullock and Brehme (2002)
- Indirectly affects other aqueous species
- modifies the minimum time step used in the
numerical solution when the mercury species have
the fastest rate of change. - mercury chemistry requires using the gas phase
HO2, HOCl and Cl2 based on Lin et al. (1998). - affects pH and ion balance in cloud droplets
8In-Cloud Chemistry (cont.)
- Possible effects from changes
- change particulate sulfate
- wet deposition of HO2, HOCl and Cl2
- can produce HOCl from clouds with low or no
participation.
9Inline Vertical Diffusion
- Aerosol emissions includes routines for
particulate mercury and other metals - Emissions includes source of Cl2 over open
oceans. - Set off by default
- Set on with the environment variable,
CTM_CL2_SEAEMIS - Source mimics implied heterogeneous production
for sea salt aerosols (Spicer et al. 1998) - Knipping and Dadbub (2002 and 2003) proposed a
mechanism but not used - reaction efficiencies are not well defined
- CB05CL_AE5_AQ does not include ClNO2 and ClONO2.
10Comparison to Standard CMAQ, i.e.,CB05CL_AE5_AQ
- Using two weekly periods in January and July 2002
- Domain covered Continental US
- grid cell had 36X36 km2 horizontal dimensions
- 14 vertical layers in s pressure coordinates
- Comparison used the weekly averages
- tile plots of differences from CB05CL_AE5_AQ,
i.e., standard model - scatter plots showing difference versus
standards prediction
11HOCl
Higher HOCl production appears higher in January
12Ozone
Ozone higher in winter and correlate with HOCL
but generally within the accuracy of the
chemistry solver.
13Impact of Ozone DifferenceBenzene
Januarys ozone differences alter OH thereby
Benzene
14Particulate Sulfate
Januarys ozone differences also have small
effect on sulfate production
15Hg Changes between CB05TXHG version 4.6 and 4.7
16Areas for further improvement
- Gas Phase Chemistry for Mercury
- explicitly representing products
- Oceanic Cl2 source
- representing heterogeneous production
- possible with the proposed SAPRC07 mechanism
- Bi-Directional Surface Flux for Mercury
- addressed science model release in version 4.7
- see release notes by Jesse Bash
- Cloud chemistry does not include Cr(III) and
Cr(VI) redox reactions
Disclaimer Although this work has been reviewed
by EPA and approved for publication, it does not
necessarily reflect their policies or views.