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Comparison of CAMx and CMAQ PM2.5Source Apportionment Estimates

Kirk Baker and Brian Timin

U.S. Environmental Protection Agency, Research Triangle Park, NC

Presented at the 2008 CMAS Conference

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Background

• Photochemical model source apportionment is a useful tool to efficiently characterize source contribution to PM2.5

• Implemented particulate source apportionment in CMAQv4.6

• Compared the source apportionment results with other model system: CAMx

• Existing inputs developed for Milwaukee pilot project used for comparison of source apportionment results

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PPTM & PSAT

• The Particle and Precursor Tagging Methodology (PPTM) has been implemented in CMAQ v4.6

• Particulate Source Apportionment Technology (PSAT) has been implemented in CAMx v4.5

• Tracks contribution to mercury and PM sulfate, nitrate, ammonium, secondary organic aerosol, and inert species

• Estimates contributions from emissions source groups, emissions source regions, and initial and boundary conditions to PM2.5 by adding duplicate model species for each contributing source

• These duplicate model species (tags) have the same properties and experience the same atmospheric processes as the bulk chemical species

• The tagged species are calculated using the regular model solver for processes like dry deposition and advection as bulk species

• Non-linear processes like gas and aqueous phase chemistry are solved for bulk species and then apportioned to the tagged species

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PM2.5 Source Apportionment Modeling for Milwaukee Pilot Project

CAMx v4.5 and CMAQ v4.612 km modeling domain4 months in 2002:

Jan, Apr, Jul, OctEvaluating 24-hr average

contributions from 11 source regions, the rest of the modeling domain, & boundary conditions

Emissions processed separately for each source region

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Region 12 – All non-tagged areas in domainRegion 13 – Boundary conditions

Source Regions

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Model Performance

• Daily 24-hr PM predictions at Milwaukee (550790026) and Waukesha (551330027) county STN monitors over all modeled days

• Model-Model estimates shown at right

• CMAQ tends to predict more nitrate than CAMx

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Model Performance

CMAQ CAMx

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Contribution Estimation

• Evaluated contribution at Milwaukee (5) and Waukesha (1) monitors

• PM2.5 = SO4+NO3+NH4+POC+EC

• Examined 1) top 10% days, 2) average over all days, and 3) compared daily estimates– Days included in top 10% analysis: Q1=6, Q2=6, Q3=0,

Q4=3

• Contribution from 11 source regions (counties), ICBC, all other non-tagged sources

• Did not track SOA due to low model estimations and resource constraints

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Total PM2.5 Contribution Estimation

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0.5

1

1.5

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2.5

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3.5

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4.5

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1 2 3 4 5 6 7 8 9 10 11

Source Region

Co

nc

en

tra

tio

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/m3

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CMAQ Top Days CAMx Top Days CMAQ All Days CAMx All Days

# Source Region1 Milwaukee2 Washington3 Ozaukee4 Waukesha5 Racine6 Sheboygan + Fond du Lac7 Dodge + Jefferson + Walworth8 Kenosha9 Cook10 Lake(IL) + McHenry + DuPage + Kane11 Lake(IN) + Porter + Will

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24-hr Avg Total PM2.5 Contribution Estimation: Top 10% Days

# Source Region1 Milwaukee2 Washington3 Ozaukee4 Waukesha5 Racine6 Sheboygan + Fond du Lac7 Dodge + Jefferson + Walworth8 Kenosha9 Cook10 Lake(IL) + McHenry + DuPage + Kane11 Lake(IN) + Porter + Will

CMAQ CAMx

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CMAQ

CAMx

4-month average total PM2.5 contributions from source areas 1-6

Region = 1 2 3 4 5 6

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CMAQ

CAMx

4-month average total PM2.5 contributions from source areas 7-11

Region = 7 8 9 10 11

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Distribution of 24-hr avg Contribution Estimations

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24-hr avg Contributions estimated by CMAQ and CAMx

Specie r2 CVSO4= 0.82 128NO3- 0.59 218NH4+ 0.78 132EC 0.89 91OC 0.93 97*N = 20,111

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24-hr avg Contributions estimated by CMAQ and CAMx

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24-hr avg Contributions estimated by CMAQ and CAMx

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24-hr avg Contributions estimated by CMAQ and CAMx

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Domain Maximum 24-hr avg Initial Condition Contribution

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Remarks

• CMAQ estimates more nitrate and as a result estimates larger nitrate contributions

• CMAQ seems to estimate larger local contributions from primarily emitted species

• Spatial extent of average contributions similar between models

• Average contributions over high model days very similar at the Milwaukee/Waukesha monitors

• Initial contributions drop out of model after 5-7 days• Would like to compare with CMAQ-DDM for future work

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Acknowledgements

• Tom Braverman, US EPA

• ICF International (Sharon Douglas and Tom Myers)

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Kenosha County 24-hr max contribution

Sulfate

Nitrate

Primary OC

JAN APR JUL OCT