DRAFT

METEOROLOGICAL DATA PROCESSING 

USING AERMET

FOR HEM3

US EPA 

Air Toxic Assessment Group

RTP NC 27711

September, 2014
Meteorological Data Processing using AERMET December 2013

For HEM3

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BACKGROUND

The AERMOD meteorological processor, AERMET, and its supporting modeling system 

(AERSURFACE and AERMINUTE) were used to process one year of meteorological 

data for over 800 observation stations across the continental United States, Alaska, 

Hawaii, and Puerto Rico.

METEOROLOGICAL DATA

To estimate the boundary layer parameters required by AERMOD, AERMET requires 

hourly surface weather observations (which may include hourly values calculated from 1-

minute data) and the full (i.e., meteorological variables reported at all levels) twice-daily 

upper air soundings. The surface and upper air stations are paired to produce the required 

input data for AERMOD. 

USEPA meteorologists obtained calendar year 2011 Integrated Surface Hourly Data 

(ISHD) for over 800 Automated Surface Observation System (ASOS) stations spanning 

the entire US, as well as Puerto Rico and the US Virgin Islands, from the National 

Climatic Data Center (NCDC). To support AERMET, ASOS 1-minute data for each 

surface station were also obtained from NCDC in a DSI 6405 format.

Further, upper air sounding data for the same time period for over 80 observation sites 

were obtained from the “NOAA/ESRL” online Radiosonde Database. These datasets 

were produced by ESRL in Forecast Systems Laboratory (FSL) format. Appendix 1 lists 

the surface stations, as well as the location, ground elevation, and anemometer height for 

each station. Figure 1 is a map that shows the locations of all the surface stations. 

Appendix 2 lists the upper air stations and their locations.

AERMET PROCESSING

Utilizing the AERMET meteorological data preprocessor, and the ASOS surface and FSL 

upper air stations, surface and profile files for input into AERMOD were generated 

nationwide. The surface stations were paired with representative upper air stations by 

taking the upper air station closest to each surface station. The AERSURFACE tool was 

used to estimate the surface characteristics for input into AERMET utilizing land cover 

data surrounding the surface station. In addition, the AERMINUTE preprocessor was 

used to process 1-minute ASOS wind data for input into AERMET. Table 1 outlines the 

approach/inputs each of the data preprocessors and tools used to generate the AERMOD

meteorological data.
Meteorological Data Processing using AERMET December 2013

For HEM3

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Figure 1. Surface Stations
Meteorological Data Processing using AERMET December 2013

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Table 1. AERMET Processing Options

AERMET Options Version 13350 1

ASOS Site Yes

Surface Data Format NCDC TD-3505 (ISHD)

Upper Air Data Format FSL, all levels, tenths m/s

Wind Speed Threshold 0.5 m/s

Beta Option (U*) Yes

AERMINUTE Options Version 11325

Include 1 minute ASOS 

Data

Yes, where available TD-6405 

format

AERSURFACE Options Version 13016

Landcover data USGS NLCD92 GeoTIFF format 

(except Alaska and Hawaii which 

used 2001 landcover data)

Radius for Surface 

Roughness Calculations

1 km

Site Characteristics Airport Site (where applicable)

Arid Regions for all sites in AZ, 

NM, UT only

Temporal resolution Monthly, 12 sectors

Site Surface Moisture Average

Snow Cover Late Winter/Winter without 

continuous snow cover – all states 

(except Alaska where we used 

continuous snow)

1 : generated with the pre-public release version of AERMET 13350.

RESULTS

Beginning with version 12345, AERMET allows for a minimum wind speed of 0.5 m/s to 

be utilized when processing monitoring stations that are equipped with sonic 

anemometers and for an adjustment to the surface friction velocity (u*). The public 

version of AERMET available at the time we conducted the processing of this data did 

not include the surface friction velocity adjustment. Also at the time, an updated version 

of AERMET (and AERMOD) was under development that incorporated further surface 

friction velocity adjustments to AERMET version 12345. In anticipation of the update, 

EPA processed meteorological data using a pre-public release version of AERMET and 

incorporated the updated surface friction velocity adjustment in the output. It was EPA’s 

judgement that the pre-public release version of AERMET would generate AERMOD 

ready meteorological data very close to that generated with the 13350 version of 

AERMET. The AERMET meteorological data posted on the EPA’s FERA (Fate, 

Exposure, and Risk Analysis) website under the HEM model page was generated with the 

pre-public release version of AERMET 13350. 
Meteorological Data Processing using AERMET December 2013

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ly, USEPA meteorologists ran AERMOD using a model plant. Further, the surface files 

were examined for completeness. If more than 10 percent of the data were missing, the 

station was not considered suitable for the HEM-3 meteorological database. In all, 824 

met station pairs ran successfully and will be included in the HEM-3 meteorological 

library. A summary of these station pairs are presented in Appendix 3 of this document.