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Regional Modeling of The Atmospheric Fate and Transport of Benzene and Diesel
Particles with CMAQ
Christian Seigneur, Betty Pun
Kristen Lohman, and Shiang-Yuh Wu
AER
San Ramon, CA
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Acknowledgments
Project A-42-1 funded by the Coordinating Research Council (CRC) and the U.S. DOE Office of FreedomCAR and Vehicle Technologies through the National Renewable Energy Laboratory (NREL)
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Air Toxics Regional Model
• CMAQ
– with benzene chemistry
– with “diesel particles” species
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Benzene Chemistry
C6H6 + OH Products
k = 1.3 x 10-12 cm3 molec-1 s -1 at 298 K
Benzene half-life of about 1 week
OH concentrations from CMAQ chemistry (CBM-IV)
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Diesel Particles
• A fixed bimodal distribution of diesel particles was assumed for the emitted and ambient diesel particles, with modes centering around 0.055 and 0.5 m.
• Dry deposition is simulated using the algorithm of Venkatram and Pleim (1999)
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Application to the Northeast
• Domain: Northeastern United States
• Period: July 11-15, 1995
• Models: 3-D nested regional model (modified CMAQ) with 12 and 4 km horizontal resolution
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Nested Modeling Domains
47
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Emission Inventories
• Benzene: National Toxics Inventory (1996) with spatial resolution by county and annual resolution
• Diesel particles: National Emission Inventory (1996) with spatial resolution by county and annual resolution
• SMOKE emission processing
– surrogate files for spatial distribution (e.g., major highways, population)
– temporal profiles (seasonal, weekday/weekend, diurnal) according to SCC
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Emissions of Benzene (moles/hr)
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Benzene Concentrations (ppm)15 July 1995, 6 a.m., 12 km resolution
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Benzene Concentrations (ppm)15 July 1995, 6 a.m., 4 km resolution
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Comparison of Simulated Urban and Rural Benzene Concentrations (ppm)
Benzene
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 24 48 72
Time from 13 July 1995
ppb
Brigantine
NYC
NYC_observed
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Benzene (ppb)Simulation vs. Measurements
Location Simulation Measurements(1)
Urban 1 - 5 0.9 - 26
Suburban -Rural
0.1 – 0.6
Remote < 0.1 0.008 – 0.2
(1) Finlayson-Pitts & Pitts, 1999
0.1 - 0.5
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Model Performance forBenzene Concentrations
12 km resolution domain
4 km resolution domain
Number of data pairs
67 35
Normalized error 53% 64%
Normalized bias 8% 40%
Correlation coefficient
0.19 0.50
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Emissions of Diesel Particles (kg/hr)
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Diesel Concentrations (g/m3)15 July 1995, 6 a.m., 12 km resolution
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Diesel Concentrations (g/m3)15 July 1995, 6 a.m., 4 km resolution
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Comparison of Simulated Urban and Rural Diesel Concentrations (g/m3)
Diesel Particles
0
2
4
6
8
10
12
14
16
0 24 48 72
Time from 13 July 1995
microgram /m
3
BrigantineNYC
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Elemental Carbon(1) (g/m3)Simulation vs. Measurements
Location Simulation(2) Measurements(3)
Urban 1 - 21 0.8 – 20
Suburban -Rural
0.2 – 2
Remote 0.005 – 0.5
(1) Elemental carbon (EC) is an operational definition of the analytical measurement technique(2) assuming 50% EC in diesel particles(3) Seinfeld and Pandis, 1998
0.5 - 2
0.05 - 0.2
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Elemental Carbon(1) (g/m3)Simulation vs. Measurements on July 15
Location Simulation(2) Measurements(3)
E. Forsythe, NJ 0.53 1.16
Washington, D.C. 1.51 1.89
(1) Elemental carbon (EC) is an operational definition of the analytical measurement technique
(2) assuming 50% EC in diesel particles
(3) IMPROVE
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Conclusion
• CMAQ was modified to simulate two air toxics: – Benzene– Diesel particles
• Regional model gives realistic atmospheric concentrations for benzene and diesel particles
• Regional background can have a significant impact on peak urban concentrations
• Elemental carbon (EC) is not a good surrogate for diesel particles because of other EC sources