Meteorological data sets processed for use in AERMOD applications are available for download. There are 26 stations available throughout South Coast AQMD’s jurisdiction. These files were developed using the U.S. EPA's AERMET processor Version 22112 and pre-processors AERMINUTE Version 15272 and AERSURFACE Version 20060.

This interactive map (https://www.aqmd.gov/assets/aermet/AERMET_files_And_HRA_Tool.html) shows the 26 meteorological stations and the South Coast AQMD Source Receptor Areas. Site details, surface characteristics, temperature ranges and AERMOD-ready meteorological data (i.e., *.sfc and *.pfl files) can be obtained by clicking on each meteorological station. The current data set labeled as Version 11 contains the most recent 5 years with complete data. Years which do not meet the completeness criteria have been excluded from the *.sfc and *.pfl files.

Map users can also visualize:

• Wind roses at all meteorological sites;
• Background concentrations of criteria pollutants consisting of pollutant maxima and design values measured at 38 sites. These are the same data reported in the “AQ-Card”; and

• Hourly background ozone data at 16 sites, during the same calendar years where the nearest meteorological station (mostly co-located with the ozone monitor) met quality control criteria.

An address search tool and a distance measuring tool are included on the map.

The raw data used in the AERMET meteorological processor is also available by request only for use on a case-by-case basis.  If AERMET will be used to develop a project-specific meteorological data set, please contact the Senior Meteorologist 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 11)

The meteorological data was processed with U.S. EPA’s AERMET Version 22112. Raw meteorological data from South Coast AQMD’s monitoring stations and the Automated Surface Observing System (ASOS) stations within South Coast AQMD’s jurisdiction were collected for the years of 2010 – 2023. Hourly wind and temperature data were collected from both South Coast AQMD and ASOS stations, while cloud cover and 1-minute wind data were 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. Upper air data from the Miramar (NKX) station was used for the upper air data input to AERMET. The ADJ_U* option was enabled in the calculations.

Surface characteristics, such as albedo, Bowen ratio, and surface roughness, were determined from U.S. EPA’s processor AERSURFACE Version 20060. 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. Stations in the Coachella Valley were classified as Dry regardless of the measured precipitation. Data from the 2016 USGS National Land Cover Database (NLCD), including Land Cover, Tree Canopy, and Impervious Cover, was used as the land cover input into AERSURFACE and arid region was set to “Yes”. Twelve equal wind direction sectors were used and the sectors with airports were labeled in the input into AERSURFACE. The ZORAD option was used for the calculations.

After the meteorological data was processed with AERMET, the data went through quality control. An hour was deemed complete only if temperature, wind speed, wind direction and cloud cover data were all concurrently available. Data in a given calendar year did not pass quality control if more than ten percent of measured parameters were missing in any quarter, or more than 10 percent of hours had calm winds in any quarter. Additional checks determined that there were no step changes in measured parameters, that wind roses were consistent with the terrain, that seasonal and diurnal variations were reasonable, and that wind speeds were reasonable. The most recent five years of data meeting the quality control criteria were then identified for each station, with some stations being eliminated for use in dispersion modeling applications. Several South Coast AQMD stations that had been available in the past were determined to no longer be appropriate, due to not passing the quality control criteria or due to having a nearby ASOS station available. Additionally, the ASOS stations within South Coast AQMD’s jurisdiction were included to provide robust coverage for dispersion modeling purposes.

Hourly ozone data concentration data files were also prepared for use with AERMOD’s PVMRM option. Since AERMOD requires ozone background data for every hour of the modeling period, missing data were filled in as follows:

1. Linearly interpolated ozone data when a maximum of 1 hour was missing.
2. For longer periods of missing data, substituted the maximum for each month/hour combination based on historical data at the same site. Please note that historical maxima are only based on the five years where the nearest meteorological station met the AERMOD data completeness requirements.

The timeseries plot of ozone data included in the zip archive identifies which years were used, and which substitution method was applied in each instance of missing data.

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. Turn on the wind roses and use the address search and distance measuring tools in the rightmost tab of the interactive map at https://www.aqmd.gov/assets/aermet/AERMET_files_And_HRA_Tool.html to visualize wind flows at meteorological sites close to the facility location. However please note that the closest meteorological station to the facility is not necessarily the most meteorologically representative site.  

All technical justifications 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.