In light of the release of version 11059 of AERMET, the meteorological data processor for AERMOD, the WDNR has processed updated meteorological datasets for air dispersion modeling. These meteorological datasets contain years 2006-2010 (replacing 1998-2002). A few stations will be discontinued due to non-availability of minutely wind data (a new feature of AERMET version 11059). In addition, a few new stations will be added. According to lead modeler John Roth, once the 2006-2010 datasets are released and any transition period has ended, modeling considering the 1998-2002 data will not be accepted. The WDNR is currently working on a transition plan before releasing the meteorological data on their website. In the meantime, if a facility is working on 1-hour SO2 statewide compliance modeling or conducting modeling for a Prevention of Significant Deterioration (PSD) application for PM10, PM2.5, SO2, or NOx, meteorological data can be obtained by request from John Roth.
The new meteorological data coupled with the new version (11103) of AERMOD could yield very different results depending on the stack parameters and building configuration at the facility. This is especially apparent for stacks with poor dispersion as well as volume sources. One potential reason for this difference is the availability of minutely wind speed data reduces the number of hourly "calm" observations that were processed with the previous version of AERMET ("calm" wind speed events trigger the "calms processing routine" which sets the modeled concentration to zero for the hour). In addition, the threshold for low wind speeds has been reduced from 3 knots to 1-2 knots. Thus, the combination of these factors yields a greater number of low wind speed events which could yield higher concentrations for more 1-hour events.