AERMET is the meteorological preprocessor used to prepare data into a format usable by the AERMOD modeling system. One of the four types of data ready by AERMET is hourly surface observations collected into one of several preformatted data file formats. For several years, the primary format used in AERMET’s Surface Pathway has been the Integrated Surface Hourly Database (ISHD) hosted by the National Centers for Environmental Information (NCEI).
In late 2025, NCEI announced the retirement of their Integrated Surface Dataset (ISD) program and replaced it with the Global Historical Climatology Network hourly (GHCNh) dataset. The GHCNh network includes the vast majority of the ISD data sources plus more than 100 additional ones. More information about GHCNh is available on the NCEI website.
This change is significant for AERMET because GHCNh is not yet available as a readable format for the model. The U.S. EPA is currently working on incorporation of GHCNh into AERMET as an available Surface Pathway input format. The next release of AERMET in 2026 will include this capability.
Until the U.S. EPA publishes the new version of AERMET later this year, modelers can continue to use data from the existing ISH database in the original archival TD-3505 format. Data is available through late August 2025. Because NCEI will not complete the remainder of 2025 in the TD-3505 format, modelers who need to process the most recent five-year period should continue to use data from 2020-2024 or consult with their regulatory agency for further guidance.
Lakes Environmental Software can also help with any data processing needs you may have. Further information about our meteorological data services – including the ability to process local station data – can be found on our website.