Comparison of the Industrial Source Complex and AERMOD dispersion models: case study for human health risk assessment.

15. Users Guide to the Building Profile Input Program (BPIP); EPA-454/R-93-038; U.S. Environmental Protection Agency; Office of Air Quality Planning and Standards: Research Triangle Park, NC, 1995.

16. Compendium of Reports from the Peer Review Process for AERMOD; U.S. Environmental Protection Agency; Office of Air Quality Planning and Standards: Research Triangle Park, NC, 2002; available at http://www.epa.gov/scram001/7thconf/aermod/dockrpt.pdf (accessed 2006).

17. Sorbjan, Z. Air Pollution Meteorology. In Air Quality Modeling--Theories, Methodologies, Computational Techniques, and Available Databases and Software. Vol. 1: Fundamentals; Zannetti, P., Ed.; EnviroComp Institute and A & WMA: Pittsburgh, PA, 2003; Chapter 4, pp 37-100.

18. Revised Draft User's Guide for the AERMOD Meteorological Preprocessor (AERMET); U.S. Environmental Protection Agency; Office of Air Quality Planning and Standards: Research Triangle Park, NC, 1998; available at http://www.epa.gov/scram001/7thconf/aermod/aermetug.pdf (accessed 2006).

19. Paine, R.J.; Lew, F. Consequence Analysis for ISC-PRIME, Prepared for the Electric Power Research Institute (EPRI), Palo Alto, CA; EPRI Publications No. TR-2460026, National Technical Information Service (NTIS) Publications No. PB98-156516; U.S. Department of Commerce, NTIS: Springfield, VA, 1997.

20. Schulman, L.L.; Strimaitis, D.G.; Scire, J.S. Addendum to ISC3 User's Guide. The Plume Rise and Building Downwash Model, 1997; available at http://www.epa.gov/scram001/7thconf/iscprime/useguide.pdf (accessed 2006).

21. Trinity Consultants. BREEZE ISC and AERMOD Users Guide, Version 3.5. Trinity Consultants: Dallas, TX, 2001.

22. Air Toxics Risk Assessment Reference Library, Vol. 1: Technical Resource Manual; EPA-453-K-04-001A. U.S. Environmental Protection Agency; Office of Air Quality Planning and Standards: Research Triangle Park, NC, 2004.

23. National Research Council. Science and Judgement in Risk Assessment; National Academies: Washington, DC, 1994.

24. Beychok, M.R. Fundamentals of Stack Gas Dispersion, 3rd ed. Newport Beach, CA, 1994.

About the Authors

Dr. Keith Silverman is a director and Dr. Joan Tell is a senior project engineer in the Global Safety and the Environment Department at Merck & Co., Inc. based in Whitehouse Station, NJ. Dr. Edward Sargent is the managing director of EV Sargent LLC and Dr. Zeyuan Qiu is an assistant professor in the Department of Chemistry and Environmental Sciences at New Jersey Institute of Technology, Newark, NJ. Please address correspondence to: Keith Silverman, Merck & Co., Inc., 2 Merck Drive, Whitehouse Station, NJ 08873; phone: +1-908-423-4102; fax: +1-908-735-1496; e-mail: keith_silverman@merck.com.

Keith C. Silverman and Joan G. Tell

Global Safety and the Environment, Merck & Co., Inc., Whitehouse Station, NJ

Edward V. Sargent

EV Sargent LLC., Watchung, NJ

Zeyuan Qiu

Department of Chemistry and Environmental Sciences, New Jersey Institute of Technology, Newark, NJ

RELATED ARTICLE: IMPLICATIONS

Air quality models are typically used to predict the fate and transport of air emissions from industrial sources to comply with federal and state regulatory requirements and environmental standards, as well as to determine pollution control requirements. This study compares two common models (ISC and AERMOD), the magnitude differences in ambient air concentrations predicted by the models, and the subsequent human health effects predicted using the results from the two models. Table 1. Source parameters used in the modeling. Source Type Parameters Units Site 1 Site 2 Point Height m 21.4 16.5

Diameter m 0.37 0.4

Temperature [degrees]C 25 20

Exit velocity m/sec 3.8 0.4 Area Release height m 1 1

X-length m 5 5

Y-length m 12 12 Volume Release height m 9.75 9.75

Initial lateral dimension m 5.3 5.3

Initial vertical dimension m 4.5 4.5 Table 2. The parameter values for calculating the HI and LICR. Parameter Description Value Units Site 1

ER Methylene chloride -- 7.1 x g/sec

stack [10.sup.-2]

ER Methylene chloride -- 7.0 x g/sec

area [10.sup.-3]

ER Methylene chloride -- 8.0 x g/sec

volume [10.sup.-3]

RfC Methylene chloride 1 mg/[m.sup.3]

IUR Methylene chloride 4.7 x 1/([micro]g/[m.sup.3]) Site 2 [10.sup.-7]

ER Hydrazine -- stack 2.5 x g/sec

[10.sup.-4]

ER Methylene chloride -- 7.0 x g/sec

area [10.sup.-3]

ER Methylene chloride -- 8.0 x g/sec

volume [10.sup.-3]

RfC Hydrazine 2.0 x mg/[m.sup.3]

[10.sup.-4]

IUR Hydrazine 4.9 x 1/([micro]g/[m.sup.3])

[10.sup.-3]

RfC Methylene chloride 1 mg/[m.sup.3]

IUR Methylene chloride 4.7 x 1/([micro]g/[m.sup.3])

[10.sup.-7] Notes: ER = emission rate. Table 3. Maximum off-site ground-level air concentrations predicted by the various models for both sites using a unit emission rate. Air Dispersion Averaging ([micro]g/[m.sup.3])/(g/sec) Model Period Site 1 Site 2 Point Sources

ISC Total period 6.2 52.0

AERMOD Total period 7.4 18.6

ISC 1 hr 571.2 4,907.2

AERMOD 1 hr 333.0 576.4

ISC-PRIME Total period 9.2 30.8

AERMOD-PRIME Total period 7.7 9.0

ISC-PRIME 1 hr 284.2 1,123.7

AERMOD-PRIME 1 hr 247.6 405.4 Area Sources

ISC Total period 369.4 67.4

AERMOD Total period 213.0 111.9

ISC 1 hr 34,147.3 11,765.5

AERMOD 1 hr 17,858.0 14,947.5 Volume Sources

ISC Total period 36.4 37.5

AERMOD Total period 43.8 19.7

ISC 1 hr 1,679.3 3,676.7

AERMOD 1 hr 1,399.8 702.8 Table 4. Predicted maximum HQ and LICR values. Air Dispersion HQ Model Site 1 Site 2 Point Sources

ISC 2.4 x [10.sup.-4] 1.0 x [10.sup.-1]

AERMOD 2.8 x [10.sup.-4] 3.7 x [10.sup.-2]

ISC-PRIME 3.5 x [10.sup.-4] 6.1 x [10.sup.-2]

AERMOD-PRIME 2.9 x [10.sup.-4] 1.8 x [10.sup.-2] Area Sources

ISC 1.4 x [10.sup.-3] 2.5 x [10.sup.-4]

AERMOD 8.0 x [10.sup.-4] 4.2 x [10.sup.-4] Volume Sources

ISC 1.6 x [10.sup.-4] 1.6 x [10.sup.-4]

AERMOD 1.9 x [10.sup.-4] 8.5 x [10.sup.-5] Air Dispersion LICR Model Site 1 Site 2 Point Sources

ISC 7.1 x [10.sup.-8] 2.1 x [10.sup.-5]

AERMOD 8.4 x [10.sup.-8] 7.6 x [10.sup.-6]

ISC-PRIME 1.0 x [10.sup.-7] 1.3 x [10.sup.-5]

AERMOD-PRIME 8.8 x [10.sup.-8] 3.7 x [10.sup.-6] Area Sources

ISC 4.2 x [10.sup.-7] 7.6 x [10.sup.-8]

AERMOD 2.4 x [10.sup.-7] 1.3 x [10.sup.-7] Volume Sources

ISC 4.7 x [10.sup.-8] 4.9 x [10.sup.-8]

AERMOD 5.7 x [10.sup.-8] 2.6 x [10.sup.-8]