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9th Conference on Air Qual

Modeling – A&WMA AB-3 

Comments on AERMOD 

George J. Schewe, CCM, QEP

Trinity Consultants

1717 Dixie Highway, Suite 900

Covington, KY 41011

gschewe@trinityconsultants.com
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AERMOD Comments

• Low wind speed issues• Modeling of roadways for NO2 and PM

• Problems with modeling small urban area• Need for post-processor to combine mult

AERMOD runs

• Deposition support• Adjustments for international applications
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Low Wind Speed Issues

• Many investigators report that the worst-c

AERMOD impacts occur for very low wind 

speeds, especially for low-level sources

• AERMOD has limited evaluation for these 

conditions

• ASOS use of sonic anemometer data and 

averaging of sub-hourly ASOS data will licreate more hours with very low wind spe

• AERMOD needs supplemental evaluation 

assess the accuracy of these “design concentration” predictions
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Modeling of Roadway Sou

• Short-term NO2 ,PM10 and PM2.5 concentrations are 

dominated by mobile source impacts near major r

• Roadways are characterized by enhanced turbule

low wind speeds generated by traffic itself 

• Review of data from tracer studies and adjustmen

AERMOD modeling procedures for roadway is an 

issue for EPA to pursue

• Problems - few long-term monitors near roadways 

quantification of emissions, especially PM, is ques
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Problems with Modeling Sm

Urban Sources

• Nocturnal urban mixing height (Ziu) is a f

of population

• For small populations, Ziu can be quite lo

about 200 m for a population of 50,000)

• This has been found to result in plume ca

at night for all plumes, no matter how buoleading to counter-intuitive results

• EPA should investigate this issue and co

the problem
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Need for Postprocesso

• AERMOD runs can be very long• Runs cannot be done separately and 

combined in postprocessor, as is dowith CALPUFF

• EPA should develop a system like th

the CALPUFF system, or translate 

AERMOD conc. files to CALPUFF-li

• TRC may have a draft code that can 

this
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Deposition Support

• Dry gas deposition is not included in 

implementation guides but in the 200addendum – makes for some confus

• Recommend that AERMOD guidanc

provide further implementation guidaaddress use of dry gas deposition faand the use of ANL physical paramefor common pollutants (Wesely, et.a2002)
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Adjustments for Internation

Applications

• International applications have challenge

12Z sounding times not at sunrise

• Bob Paine provided EPA (in October 200

several possible enhancements

– Swapping of 12Z and 00Z sounding time labe– Adjustment of lower part of sounding to reflec

minimum sfc temp

– Enhanced debugging output

• EPA should make these enhancements a

at least in beta test form
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AERSURFACE Comment

• Issues with AERSURFACE impleme• Sensitivity of modeling to surface 

characteristics
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Issues with AERSURFAC

Implementation

• Land use determination very localized - within 1 

– Greater chance of mismatch in surface type b

met tower and source

• For tall stack, buoyant releases, 1 km is too sho

fetch distance

• Low roughness near towers increases likelihood 

u* and low wind speed issues

• Moisture assigned only on an annual basis
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Sensitivity Test for Representativ

of Surface Characteristics

• Brode et al. have written paper for A&WM

Annual Meeting on sensitivity modeling

• We recommend use of AERSCREEN wit

different runs for met and application site 

characteristics

• If peak predictions are reasonably simila

within 10%), then assume that differencesurface characteristics have a minor effe
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AERMET Comments

• States advocating use of more recent dat• Many more calms in recent data sets – if 

considered missing as suggested in GAQnot meet 90% capture criteria

• If many calms, does CALMS preprocesso

properly? Conc artificially too low?

• Guidance needed on use of recent met d