**1 9** **th Conference on Air Quality** **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 2** **AERMOD Comments • Low wind speed issues** **• Modeling of roadways for NO 2** **and PM • Problems with modeling small urban areas** **• Need for post-processor to combine multiple AERMOD runs** **• Deposition support • Adjustments for international applications** **3 Low Wind Speed Issues** **• Many investigators report that the worst-case 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 likely create more hours with very low wind speeds** **• AERMOD needs supplemental evaluation to assess the accuracy of these “design** **concentration” predictions 4** **Modeling of Roadway Sources • Short-term NO** **2 ,PM** **10 and PM** **2.5 concentrations are** **dominated by mobile source impacts near major roadw ays** **• Roadways are characterized by enhanced turbulence and** **low wind speeds generated by traffic itself • Review of data from tracer studies and adjustments** **to AERMOD modeling procedures for roadway is an import** **ant issue for EPA to pursue** **• Problems - few long-term monitors near roadways & quantification of emissions, especially PM, is ques** **tionable 5** **Problems with Modeling Small Urban Sources** **• Nocturnal urban mixing height (Ziu) is a function of population** **• For small populations, Ziu can be quite low (e.g., about 200 m for a population of 50,000)** **• This has been found to result in plume capping at night for all plumes, no matter how buoyant,** **leading to counter-intuitive results • EPA should investigate this issue and correct** **the problem 6** **Need for Postprocessor • AERMOD runs can be very long** **• Runs cannot be done separately and combined in postprocessor, as is done** **with CALPUFF • EPA should develop a system like that of** **the CALPUFF system, or translate AERMOD conc. files to CALPUFF-like files** **• TRC may have a draft code that can do this** **7 Deposition Support** **• Dry gas deposition is not included in the implementation guides but in the 2004** **addendum – makes for some confusion • Recommend that AERMOD guidance** **provide further implementation guidance to address use of dry gas deposition factors** **and the use of ANL physical parameters for common pollutants (Wesely, et.al,** **2002) 8** **Adjustments for International Applications** **• International applications have challenges due to 12Z sounding times not at sunrise** **• Bob Paine provided EPA (in October 2007) with several possible enhancements** **– Swapping of 12Z and 00Z sounding time labels – Adjustment of lower part of sounding to reflect mo** **rning minimum sfc temp** **– Enhanced debugging output • EPA should make these enhancements available,** **at least in beta test form 9** **AERSURFACE Comments • Issues with AERSURFACE implementation** **• Sensitivity of modeling to surface characteristics** **10 Issues with AERSURFACE** **Implementation • Land use determination very localized - within 1 km** **– Greater chance of mismatch in surface type between met tower and source** **• For tall stack, buoyant releases, 1 km is too shor t of a** **fetch distance • Low roughness near towers increases likelihood of** **low u** *******and low wind speed issues • Moisture assigned only on an annual basis** **11 Sensitivity Test for Representativeness** **of Surface Characteristics • Brode et al. have written paper for A&WMA 2008** **Annual Meeting on sensitivity modeling • We recommend use of AERSCREEN with** **different runs for met and application site surface characteristics** **• If peak predictions are reasonably similar (say, within 10%), then assume that differences in site** **surface characteristics have a minor effect 12** **AERMET Comments • States advocating use of more recent data sets** **• Many more calms in recent data sets – if considered missing as suggested in GAQM, does** **not meet 90% capture criteria • If many calms, does CALMS preprocessor work** **properly? Conc artificially too low? • Guidance needed on use of recent met data**