Implications of AERMOD on a Chemical Plant William B. Jones Roger P. Brower Zephyr Environmental Corporation Columbia, Maryland Presented at 100 th Annual AWMA Conference and Exhibition Pittsburgh, PA June 26, 2007

Outline of Presentation Background on project Comparative Modeling –ISC3 –AERMOD Conclusions

Background on Project Chemical plant in southwestern Louisiana Several permitting efforts required modeling over the past few years (modeling done with ISC3) November 9, 2006: AERMOD replaced ISC3 as preferred dispersion model Chemical plant was curious as to what effect going from ISC3 to AERMOD would have

Three projects examined Vinyl Acetate –Modeling performed in 2005 –In support of Title V application for Plant’s polyethylene manufacturing complex Butadiene –Modeling performed in 2003 –In support of revised Title V application for Plant’s ethylene/styrene manufacturing complex PM10 –Modeling performed in 2003 –In support of “retroactive” PM10 NAAQS and PSD Increment modeling

Comparative Modeling Vinyl Acetate Original ISC3 modeling –Initially only Plant sources, then offsite sources –Flat terrain (no receptor elevations) –Meteorological data from 2004 (Lake Charles surface and upper air) AERMOD modeling –Plant sources only –Flat terrain (no receptor elevations) –Meteorological data from 2004 (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

LDEQ Default Meteorological Values Taken from “Developing State-Wide Modeling Guidance for the Use of AERMOD, A Workgroup’s Experience” (Presented at 2005 Louisiana AWMA Fall Conference)

Comparative Modeling Vinyl Acetate: ISC3 Results Source Highest predicted 8-hr concentration (ug/m3) BDRYER BDRYER BEXTRDR36.50 BPELLET822.22

Comparative Modeling Vinyl Acetate: AERMOD Results Source Highest predicted 8-hr concentration (ug/m3) BDRYER BDRYER BPELLET BPELLET431.90

Comparative Modeling Vinyl Acetate: Q-Q Plot, AERMOD and ISC3

Comparative Modeling Vinyl Acetate Observations Highest contributing source is same with ISC3 and AERMOD Highest source-specific impacts for each model roughly the same AERMOD consistently over predicts relative to ISC3 (for highest 8-hr concentrations)

Comparative Modeling Butadiene Original ISC3 modeling –Initially only Plant sources, then offsite sources –Flat terrain (no receptor elevations) –Meteorological data from 2000 (Lake Charles surface and upper air) AERMOD modeling –Plant sources only –Flat terrain (no receptor elevations) –Meteorological data from 2000 (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

Comparative Modeling Butadiene: ISC3 Results Source Highest predicted annual concentration (ug/m3) 1296_D WPT35_ _96C WPT34_ _D

Comparative Modeling Butadiene: AERMOD Results Source Highest predicted annual concentration (ug/m3) 5_89A_S _89A_S WPT34_ _89A_W _89A_S

Comparative Modeling Butadiene: Q-Q Plot, AERMOD and ISC3

Comparative Modeling Butadiene Observations Major contributing sources in ISC3 are not consistent with those in AERMOD Highest source-specific impacts for AERMOD are higher (roughly an order of magnitude) than ISC3 AERMOD consistently over predicts relative to ISC3 (for highest annual concentrations)

Comparative Modeling PM10 Original ISC3 modeling –Initially only Plant sources, then offsite sources –24-hr and Annual NAAQS and PSD Increment –Flat terrain (no receptor elevations) –Meteorological data from (Lake Charles surface and upper air) AERMOD modeling –Plant and offsite sources –24-hr NAAQS only –Flat terrain (no receptor elevations) –Meteorological data from (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

Comparative Modeling PM10: ISC3 Results (1996) Source Highest second-high predicted 24-hr concentration (ug/m3) LC_COAL _ FIRE_ CIT13_ _

Comparative Modeling PM10: AERMOD Results (1996) Source Highest second-high predicted 24-hr concentration (ug/m3) LC_COAL FIRE_ STY20_ _ _

Comparative Modeling PM10: Q-Q Plot, AERMOD and ISC3 (1996)

Comparative Modeling PM10 Observations Major contributing sources in ISC3 are consistent with those in AERMOD –The two Plant sources in the Top 5 for ISC3 and AERMOD only had increases in their predicted 24-hr concentrations of 20% and 12% going from ISC3 to AERMOD (larger increases from offsite sources) Highest source-specific impacts for AERMOD are higher than ISC3 AERMOD and ISC3 are consistent in lower concentrations (AERMOD sometimes slightly lower), but at higher concentrations AERMOD over predicts relative to ISC3 (for highest second-high concentrations)

ConclusionsConclusions Examined vinyl acetate, butadiene, and PM10 modeling AERMOD nearly always predicted higher concentrations than ISC3 –For some lower PM10 concentrations AERMOD slightly under predicted relative to ISC3 Plant should exercise caution in future permitting efforts that involve updated previous dispersion modeling analyses

Contact Information Zephyr Environmental Corporation Little Patuxent Parkway, Suite 320 Columbia, Maryland Bill Jones ; visit us at and