Aug 07, 2017

The most recent scientific updates to U.S. EPA’s AERMET meteorological data processing tool (version 16216) include a new regulatory default option, ADJ_U*. This new option, which was officially approved for regulatory use in May 2017 after an approximately three-year beta testing period, addresses a long-standing issue with AERMOD and is of interest to many industries because for near-ground-level sources, it can reduce maximum modeled concentrations by as much as 50%.

Most existing AERMOD meteorological data, including that provided by many regulatory agencies, does not yet incorporate this new option. The BREEZE Data Team can provide updated meteorological data that does include the option and complies with all regulatory standards and guidance. 

Detailed Excerpt: 

New U.S. EPA modeling guidance (Appendix W) has officially taken effect as of May 21, 2017. One immediate impactful change in the new guidance is the approval of the “ADJ_U*” meteorological data processing option as a regulatory standard. This new option can have a significant effect on model results, and is not incorporated into older AERMOD meteorological data sets that are still in widespread use. Some basic facts about ADJ_U*: 

  • Designed to counteract AERMOD’s tendency to overpredict concentrations under low wind speed, stable atmosphere conditions (typical nighttime environment) 
  • Reduces peak modeled concentrations substantially in many cases 
  • Affects primarily sources close to the ground (fugitive sources and shorter stacks) 
  • Approved by U.S. EPA as a standard model option (special approval no longer required) 
  • Functions by modifying a turbulence parameter called surface friction velocity (u*) that is calculated by AERMET, effectively adding some additional mechanical turbulence to the modeled atmosphere for the met conditions that tend to cause AERMOD to overpredict concentrations 


In a test case using a U.S. Gulf Coast location with a mix of source types (ground-level fugitives and stack sources), near-ground level sources were found to have up to a 51% reduction in maximum 1-hour ground level concentrations when using ADJ_U*. 

The regulatory standard version of ADJ_U* was issued as part of U.S. EPA’s late-2016 update to AERMET. This means meteorological data processed before late 2016 does not incorporate the option and the meteorological data provided by many regulatory agencies has not yet been updated with the option. 

The BREEZE Data Team can help you determine if your meteorological data is using the new ADJ_U* option and, if it is not, can process a new meteorological dataset for you that uses the option. We routinely process meteorological data for locations around the world, complying with the latest regulatory requirements and guidance from U.S. EPA and other U.S. and international regulatory agencies. In addition to processing meteorological data for a large base of industry and air quality consulting clients, BREEZE has completed several projects assisting state regulatory agencies with updating AERMOD meteorological data across their entire state, allowing the agency to provide standardized, up-to-date meteorological data to all industries and organizations performing dispersion modeling in the state. These projects are typically done according to the exact preferences and standard practices of the particular regulatory agency and detailed documentation of the AERMET processing methodology (together with all input and output files from the data processing) are included. If you would like to receive up-to-date (including ADJ_U*), AERMOD-ready meteorological data, or to ask questions about ADJ_U* and other recent changes to AERMET, contact the BREEZE Data Team at worldgeodata@trinityconsultants.com or +1 972-661-8881.