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

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)

Air Toxics Regional Model

• CMAQ

– with benzene chemistry

– with “diesel particles” species

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)

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)

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

Nested Modeling Domains

47

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

Emissions of Benzene (moles/hr)

Benzene Concentrations (ppm)15 July 1995, 6 a.m., 12 km resolution

Benzene Concentrations (ppm)15 July 1995, 6 a.m., 4 km resolution

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

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

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

Emissions of Diesel Particles (kg/hr)

Diesel Concentrations (g/m3)15 July 1995, 6 a.m., 12 km resolution

Diesel Concentrations (g/m3)15 July 1995, 6 a.m., 4 km resolution

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

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

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

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