Meteorological data sets processed for use in AERMOD applications are available for download. There are 24 stations available throughout the South Coast Air Basin. These files were developed using the U.S. EPA's AERMET processor and pre-processors AERMINUTE Version 15181 and AERSURFACE Version 13016. The meteorological data files are suitable for use with the most recent version of AERMOD (Version 16216r).
Table 1 lists the 24 stations with AERMOD-ready meteorological data (i.e., *.sfc and *.pfl files) that are processed with the ADJ_U* option. The current data set is labeled as Version 9, with 5-years of available data between the years 2010 - 2016. More details on the Version 9 data set are provided below.
Version 9 Meteorological Stations List - Provides the full station list, abbreviations, year's availability, geographical information, and surface characteristics of each meteorological station. (PDF, 272kb)
The raw data used in the AERMET meteorological processor is also available by request only for use on a case-by-case basis. In the event that AERMET will be used to develop a project-specific meteorological data set, please contact South Coast AQMD modeling staff and provide a protocol to support the processing of meteorological data. The protocol should include an explanation of why AERMET processing is necessary, why new surface characteristics are more appropriate, AERSURFACE input and output files, processing methodologies, options used in AERMET, and other supporting information.
Methodology for Processing Meteorological Data for AERMOD Applications (Version 9)
The meteorological data was processed with U.S. EPA’s AERMET Version 16216. Raw meteorological data from South Coast AQMD’s monitoring stations and the Automated Surface Observing System (ASOS) stations were collected for the years of 2010 – 2016. Hourly wind and temperature data were collected from both South Coast AQMD and ASOS stations, while cloud cover and 1-minute wind data was only available from the ASOS stations. The ASOS 1-minute wind data was processed with U.S. EPA’s processor AERMINUTE Version 15272 and included in AERMET for ASOS stations with the use of a wind speed threshold of 0.5 m/s, which is consistent with U.S. EPA’s guidelines.
Surface characteristics, such as albedo, Bowen ratio, and surface roughness, were determined from U.S. EPA’s processor AERSURFACE Version 13016. Each station’s Bowen ratio varies by year based on the year’s precipitation total compared to the 30-year climatological average precipitation. This comparison resulted in a year being classified as Average, Dry, or Wet. For the period of 2010 – 2016, most years fell into the Dry category, with exceptions in 2010 and 2016. Data from the 1992 USGS Land Use and Land Cover dataset was used as the land cover input into AERSURFACE and arid region was set to “Yes”.
After the meteorological data was processed with AERMET, the data went through QA/QC to determine if it passed the U.S. EPA’s threshold of less than ten percent missing data by quarter and less than 15 percent calm hours by quarter. The most recent five years of data meeting the QA/QC criteria were then determined for each station, with some stations being eliminated for use in dispersion modeling applications. A number of South Coast AQMD stations that had been available in the past were determined to no longer be useable for this update, due to not passing the U.S. EPA’s QA/QC criteria, the station being discontinued, or due to having a co-located ASOS station available. Additionally, the ASOS stations within the Basin were included to provide robust coverage for dispersion modeling purposes.
ADJ_U*
The ADJ_U* option was specified in AERMET for all stations found in Table 1. ADJ_U* is now a regulatory option in the AERMOD modeling system that adjusts the surface friction velocity parameter in the surface file (*.sfc) to improve model performance for sources that have peak concentrations under low wind, stable atmospheric conditions. The ADJ_U* option should only be applied to ASOS data or site-specific meteorological stations that do not include turbulence data. All of the stations that South Coast AQMD processed meet these requirements, as turbulence data is not collected at South Coast AQMD monitoring stations.
If meteorological data without the ADJ_U* option is needed for any of the Version 9 stations, please submit a request to South Coast AQMD staff listed on this page. Data will be processed on a case-by-case basis and will typically require an 8 – 12 week wait time based on staff availability.
Choosing the Appropriate Meteorological Station for Modeling
The meteorological station that best represents the facility’s meteorological conditions (such as prevailing winds), terrain, and surrounding land use should be used in all modeling analyses. This means that the closest meteorological station to the facility is not always the most representative meteorologically.
All technical justification used in choosing the appropriate meteorological station for dispersion modeling and health risk assessments should be included in the report submitted with the analysis and all electronic modeling files. Please contact South Coast AQMD modeling staff for questions related to choosing the most appropriate meteorological station for your analysis.