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AERMET Made Easy – Selecting Weather Stations

“When using National Weather Service (NWS) data for AERMOD, data representativeness can be thought of in terms of constructing realistic planetary boundary layer (PBL) similarity profiles and adequately characterizing the dispersive capacity of the atmosphere.  As such, the determination of representativeness should include a comparison of the surface characteristics (i.e., zo, Bo and r) between the NWS measurement site and the source location, coupled with a determination of the importance of those differences relative to predicted concentrations.” – AERMOD Implementation Guide

Say what? What does this even mean? More importantly, how would anyone put this into action to select a representative weather station for use with AERMET and AERMOD?

A Framework for decisions in dispersion modeling

To put the guidance into action, you should base your representativeness on four criteria:

  • Proximity of the NWS measurement site to the source location;
  • Land use comparison between the NWS measurement site and the source location;
  • Presence of large geographic features between the NWS measurement site and the source location;
  • Wind pattern and climate comparison between the NWS measurement site and the source location.

Making a Decision

To help further along your decision-making process, as well as to document your ideas for public record, you need objective data.  Listed below is where to find the information (data and tools) you need to make an informed decision on which NWS stations to select.

For proximity comparisons, the location of NWS stations and the application site are needed. The latitude and longitude coordinates of weather stations can be found from three sources:

Once you have the coordinates, you will need an interface to view and compare locations. Here are three potential tools you can use:

For land use comparisons, land use map data can be found at https://www.mrlc.gov/viewerjs/.

The land use maps have a few formats for use with GIS software. You can also use the NaviKnow online land use tool available at http://landuse.naviknow.com/. Create a free user account to use the tool. An example of how to use the tool can be seen in the following video https://vimeo.com/288040452 .

To determine if there are any significant geographic features between a NWS station and an application site, using Google Maps (https://www.google.com/maps) should be sufficient. You can view terrain in 3-D.

To compare wind roses of multiple NWS stations, if there is more than one, wind rose data can be found at http://mrcc.isws.illinois.edu/CLIMATE/ . There is a wealth of other meteorological data available at this site.

Climatological data, such as 30-year average monthly rainfall and temperature data (minimum, maximum, and mean) can be found at http://www.prism.oregonstate.edu/recent/. These data are in a variety of formats depending upon how you want to use it.

Summarizing

Now, when having to select NWS weather stations for your AERMOD modeling analysis, you can follow this framework to aid in your decision-making documentation process and use the data in the links provided.

If you found this article informative, there is more information at  http://learn.naviknow.com with a list of  past webinar mini-courses. Every Wednesday (Webinar Wednesday), NaviKnow offers FREE webinar mini-courses on topics related to air quality dispersion modeling and air quality permitting. If you want to be on our email list, reach out to me at  [email protected].

One of the goals of NaviKnow is to create an air quality professional community to share ideas and helpful hints like those covered in this article.  If you found this article helpful, please share with a colleague.

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