When it was read to you as a child or when you were reading it to children, Dr. Seuss’ “The Places You’ll Go” describes life as one big wonderous wandering adventure.
When it comes to dispersion modeling, the last thing I want is an adventure. I guess I am getting old. When I have a modeling project to do, I just want to get all the input together, run it, process the result, write the report, and be done. Bing, bang, boom, done. Unfortunately, the reality of performing dispersion modeling is not so straightforward. There is always some kind of adventure to go on.
To put your dispersion modeling analysis together, you need data, lots of data. To get all the data you need, you will have to go several locations as there is no one place to get it all. These are the type of adventures that I really do not like at all.
The earth is not flat, so to have your sources, building, and receptors accurately represented spatially, you need elevation data to determine the elevations at each point. For the USA, the best (accurate, reliable, and defensible) elevation data is available from the U.S. Geological Survey (USGS).
To obtain elevation data for the USA, go to, https://www.mrlc.gov/viewerjs/. Make sure you know the extent of your receptor grid so you download all the files you need.
If your site is in Canada, you can obtain elevation data at http://ftp.geogratis.gc.ca/pub/nrcan_rncan/elevation/cdem_mnec/. I personally have not use these data, but I would believe it is compatible with AERMAP.
To perform dispersion modeling, you will need meteorological data as input. The meteorological data processor for AERMOD is AERMET. AERMET is executed in three stages, with each stage having a different data input.
For stage 1, you will need data for hourly surface observations and upper air soundings. In addition, you will need data about the surface and upper air stations, such as their official identifiers, location, elevation, and time zone. All these data can be found at ftp://ftp.ncdc.noaa.gov/pub/data/noaa, for surface observations, and https://www.esrl.noaa.gov/raobs/, for upper air soundings. Once you have all of your required input data downloaded and decompressed, you can execute Stage 1 of AERMET.
Stage 2 of AERMET may involve having to execute an AERMET companion program, AERMINUTE. AERMINUTE fine tunes the hourly data from stage 1 but processing either one-minute or five-minute surface observations. The data necessary for AERMINUTE can be found at ftp://ftp.ncdc.noaa.gov/pub/data/asos-onemin/ for one-minute data and ftp://ftp.ncdc.noaa.gov/pub/data/asos-fivemin/ for five-minute data. The input data for AERMINUTE come in monthly blocks, so you will need to download multiple files.
Another input for AERMINUTE is the date when instrumentation was updated at the surface weather station. These dates can be found at http://www.weather.gov/ops2/Surface/documents/IFW_stat.pdf.
In stage 3 of AERMET, you will need to derive your own values for the surface characteristics noontime albedo, Bowen ratio, and roughness length or use the companion program AERSURFACE to calculate these values. The input data for AERSURFACE is the national land cover dataset for 1992 (NLCD 1992). The NLCD 1992 can be found at the same location as the terrain data, https://www.mrlc.gov/viewerjs/. When you download the data, make sure you select the file format compatible with AERSURFACE
Ambient Monitoring Data
When performing dispersion modeling for criteria pollutants, you will have to provide a background concentration from an existing ambient air monitor. Monitoring data can be found at https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Raw, and https://www.epa.gov/air-trends/air-quality-design-values.
You can find monitor identifier, location, and pollutant concentrations for applicable averaging times corresponding to the national ambient air quality standards (NAAQS).
Off Site Emission Sources
When performing NAAQS analysis, if your project exceeds the significance impact level (SIL) for a pollutant standard, then you will be required to perform a cumulative analysis for that pollutant which is to include emissions from all sources within 50 kilometers or more of the project location.
The data for emission sources not associated with the project or even the project site, typically can be obtained from the regulatory agency that will be reviewing the NAAQS analysis. Depending upon how close your project is to neighboring states, you may have to contact and coordinate with multiple state and local agencies.
When you are putting together your next dispersion modeling analysis, keep in mind you may have to go to up to a dozen websites to find the information you need. If you know where to go, you can save yourself a lot of time and effort but you are still going to spent a good amount of time compiling, reformatting, and documenting everything you use.
Wouldn’t it be really helpful if ALL of the information listed above just magically found its way into your analysis and populated all of your input files so you could concentrate on the specific issues or nuance related to your project? Give us time. We are working on it.
If you found this article informative, there is more helpful and actionable information for you. Go to http://learn.naviknow.com to see a list of past webinar mini-courses. Most 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, drop me a line at firstname.lastname@example.org.
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. So if you found this article helpful, please share with a colleague.