On 07/24/2015, EPA released an updated version of the AERMOD model. Key technical changes in the new version are as follows:
- Includes option in AERMET to adjust the surface friction velocity (u*) to address issues with AERMOD model over prediction under stable, low wind speed conditions.
- Includes a low wind option in AERMOD to address issues with model over prediction under low wind speed conditions. The low wind option will increase the minimum value of the lateral turbulence intensity (sigma-v) from 0.2 to 0.3 and adjusts the dispersion coefficient to account for the effects of horizontal plume meander on the plume centerline concentration.
- Modifications to AERMOD formulation to address issues with over prediction for applications involving relatively tall stacks located near relatively small urban areas.
- Includes regulatory default options to address plume rise for horizontal and capped stacks.
- Includes buoyant line source option based on the BLP model.
- Updates to the NO2 Tier 2 and Tier 3 screening techniques coded within AERMOD for assessments related to 1 hour NO2 standards. Tier 2 technique will be ARM2 which is based on hourly measurements of the NO2 to NOx ratios and provides more detailed estimates of this ratio based on the total NOx present. For Tier 3 technique, the existing detailed screening options of the Ozone Limiting Method (OLM) and PVMRM which have been available as non-regulatory, non-default options in AERMOD for many years is formally incorporated as regulatory options.
Please contact your EPS consultant for more information.