{"slug":"is-aermod-free","title":"Is AERMOD Free? EPA Download, Paid Interfaces and the Real Costs","excerpt":"AERMOD is free from the US EPA — but a study is more than the model. What you can download at no cost, how to run it yourself, what paid interfaces add, and how to choose between doing it yourself, a licence, online software and a modelling service.","date":"2026-11-04","author":"DS Technoverse","image":"/blog-images/aermod-software/aermod-report-cover-contents.webp","category":"Air Dispersion Modelling","tags":["is AERMOD free","AERMOD free download","AERMOD software price","AERMOD licence","free air dispersion model","AERMOD View alternative","AERMOD demo"],"content":"Yes — AERMOD is free. The US Environmental Protection Agency develops it as public software and publishes the programs, the source code and the user guides at no charge. Anyone can download it and run it.\n\nThat answer is true and, on its own, misleading. A dispersion study is not just a model run: it is meteorological data that has to be found, checked and processed; a receptor grid; terrain and buildings where they matter; post-processing into tables and maps; a comparison with the standards; and a report a regulator will accept. The model is free. The work around it is where the cost, the time and the risk sit.\n\nThis article explains exactly what you can get for free, how to run the free EPA programs yourself, what the paid desktop interfaces add, what online software changes, and how to decide which route makes sense for your studies. It ends with what our free AERMOD Studio demo includes.\n\n![Cover and contents of an AERMOD Studio report from a dummy test study](/blog-images/aermod-software/aermod-report-cover-contents.webp)\n\n## What the US EPA Gives You for Free\n\nAERMOD has been the EPA's preferred model for near-field dispersion of industrial emissions since 2005, listed in the Guideline on Air Quality Models (Appendix W to 40 CFR Part 51). The EPA distributes it, with the programs that prepare its inputs, through its Support Center for Regulatory Atmospheric Modeling (SCRAM) website. All of the following are free:\n\n| Program | What it does | Needed for |\n|---|---|---|\n| AERMOD | The dispersion model: hourly concentrations at every receptor, averaged into the standard periods | Every study |\n| AERMET | Turns surface weather observations and upper-air soundings into AERMOD's surface and profile files | Every study |\n| AERMAP | Assigns terrain elevations to sources and receptors from digital elevation data | Sites with non-flat terrain |\n| BPIP-PRIME (BPIPPRM) | Calculates building dimensions for stacks affected by building downwash | Stacks near buildings |\n| AERSURFACE | Derives surface characteristics from land-cover data | Mainly US sites (uses the US land-cover database) |\n| AERMINUTE | Processes one-minute wind data to reduce calms | US airports with one-minute data |\n| AERSCREEN | A screening version of AERMOD for one source with worst-case meteorology | Quick conservative checks |\n\nEach comes as a Windows executable, with Fortran source code that can be compiled for Linux or other systems, a user's guide, a model formulation document and test cases. There is no licence fee, no registration and no limit on use.\n\nWhat the EPA does not give you is a graphical interface, meteorological data for your site, maps, or a report. Those are the parts you either do yourself, buy, or have someone do for you.\n\n## Running the Free EPA AERMOD Yourself\n\nIt is entirely possible to run a regulatory study with nothing but the free programs. Here is what that involves.\n\n### Step 1: Download the programs\n\nFrom the EPA SCRAM website, download the AERMOD and AERMET executables (and AERMAP and BPIP-PRIME if your site needs them). Unzip them into a working folder. On Windows they run from the command prompt; there is nothing to install.\n\n### Step 2: Get meteorological data\n\nAERMET needs hourly surface observations — wind speed and direction, temperature, cloud cover, pressure, humidity — and upper-air soundings, normally from the nearest representative stations, for the whole study period. For most of the world, the public sources have been the NOAA Integrated Surface Database (ISD) for surface data and the Integrated Global Radiosonde Archive (IGRA) for upper air.\n\nThis step changed in 2025: NOAA's legacy ISD station files stopped updating in late August 2025, so studies of later periods need another surface data source. We explain the alternatives — site measurements, NOAA's newer hourly product, NASA POWER and reanalysis data — in [NOAA ISD stopped in 2025: meteorological data for AERMOD now](/blog/noaa-isd-data-aermod-2025/).\n\n### Step 3: Run AERMET\n\nAERMET is controlled by a text file that names the input files, the station locations, the time zone, the processing options and the surface characteristics (albedo, Bowen ratio, roughness length) for the area around the site. It produces a surface file (.sfc) and a profile file (.pfl). Getting the station identifiers, the time offset and the surface characteristics right is where most first attempts go wrong; our article [AERMET explained](/blog/aermet-meteorological-data-preprocessing/) goes through the stages.\n\n### Step 4: Write the AERMOD control file\n\nAERMOD reads a \"runstream\" file organised in pathways: control options (CO), sources (SO), receptors (RE), meteorology (ME) and output (OU). A minimal file for one stack, one pollutant and a simple grid looks like this:\n\n    CO STARTING\n       TITLEONE  Example boiler stack - SO2\n       MODELOPT  DFAULT CONC FLAT\n       AVERTIME  1 24 PERIOD\n       POLLUTID  OTHER\n       RUNORNOT  RUN\n    CO FINISHED\n    SO STARTING\n       LOCATION  STK1  POINT  594590.0  2513371.0  550.0\n       SRCPARAM  STK1  4.0  35.0  413.15  12.0  1.2\n       SRCGROUP  ALL\n    SO FINISHED\n    RE STARTING\n       GRIDCART  POL1 STA\n                 XYINC  592590.0 41 100.0  2511371.0 41 100.0\n       GRIDCART  POL1 END\n    RE FINISHED\n    ME STARTING\n       SURFFILE  aermet.sfc\n       PROFFILE  aermet.pfl\n       SURFDATA  42754  2025\n       UAIRDATA  42647  2025\n       PROFBASE  550.0  METERS\n    ME FINISHED\n    OU STARTING\n       RECTABLE  ALLAVE  FIRST\n       PLOTFILE  24  ALL  FIRST  so2_24.plt\n    OU FINISHED\n\nThe SRCPARAM line gives the emission rate (4.0 g/s), stack height (35 m), exit temperature (413.15 K), exit velocity (12 m/s) and inner diameter (1.2 m). Coordinates are in metres, usually UTM. A real study adds a coarser outer grid, boundary receptors, discrete receptors for villages and schools, more pollutants and more output tables — and every pollutant usually gets its own run.\n\n### Step 5: Run and read the output\n\nRunning the model is one command. AERMOD writes a long text listing with the input echo, messages, and tables of the highest values at each receptor, plus the plot files you asked for. Check the message summary for errors and warnings, and the count of missing meteorological hours, before you look at any result.\n\n### Step 6: Post-process\n\nTo turn the plot files into isopleth maps, you need a GIS or a plotting tool — QGIS, Surfer, or a short script with Python libraries such as pandas, matplotlib and pyproj. Then come the tables: maximum GLC and its location for each pollutant and period, values at sensitive receptors, the cumulative total with background, and the comparison with the standards. See [how to read AERMOD output](/blog/reading-aermod-output-contour-maps/) for what each table means.\n\n### Step 7: Write the report\n\nFinally, the report: project and source description, meteorology and why the stations were chosen, model options, receptors, results, isopleths, cumulative impact, conclusions and limitations, with the model files archived. Our guide to [what an air dispersion modelling report should contain](/blog/air-dispersion-modelling-report-contents/) lists the sections reviewers look for.\n\nNone of these steps is beyond a careful engineer. Together, for a first study, they typically take days to weeks, and the most expensive mistakes — a wrong time zone, swapped units, a coarse grid that misses the maximum, meteorology with too many missing hours — are the ones that are hardest to spot in your own work. Our article on [common AERMOD mistakes](/blog/common-aermod-mistakes/) lists the ones we see most.\n\n## What Each Free Program Expects From You\n\nThe EPA programs are free, but each needs inputs that you must find and prepare. Knowing what they are is the best way to judge how much work the free route really is for your site.\n\n### AERMET\n\nAERMET runs in stages. The first extracts and quality-checks the raw surface and upper-air data; the second merges them hour by hour; the third (METPREP) calculates the boundary-layer parameters and writes the two files AERMOD reads. You supply:\n\n- Hourly surface observations for the study period in a format AERMET reads — the NOAA ISD format for airport data, or its ONSITE format for site measurements.\n- Upper-air soundings, usually from IGRA, for the nearest representative station.\n- Station identifiers, coordinates, elevations and the time offset from GMT to local standard time (for India, five hours, entered as a negative number in AERMET).\n- Surface characteristics — albedo, Bowen ratio and surface roughness length — for the area around the site, by season and by direction sector if they vary. For US sites AERSURFACE derives them from land-cover data; elsewhere you choose them from guidance tables and justify the choice.\n- Processing options, such as how to treat missing upper-air soundings and whether to adjust the friction velocity in light winds.\n\n### AERMAP\n\nAERMAP needs a digital elevation model covering the whole receptor grid — for India, typically SRTM or a similar global data set — in a format AERMAP reads, together with the receptor and source coordinates in the same projection. It returns an elevation and a \"hill height scale\" for every receptor. Mismatched datums or projections are the classic error.\n\n### BPIP-PRIME\n\nBPIP-PRIME needs the footprint corners and heights of every building that could affect a stack — usually any building within about five times its smaller dimension (height or projected width) of the stack — and the stack locations and base elevations. Drawing buildings accurately from a site plan is slow, careful work.\n\n### AERMOD\n\nAERMOD needs everything above, plus the source parameters and emission rates, the receptors, the averaging periods and output options. Each study also involves decisions that the program will not make for you: rural or urban dispersion, the receptor spacing, whether to include the fence line, how to treat NOx, which background to add.\n\n## A Realistic Time Budget for a Do-It-Yourself Study\n\nFor a standard study — a few stacks, flat terrain, one season, five pollutants — the time goes roughly like this. The ranges are from our own experience; a first study sits at the top of each range, an experienced modeller at the bottom.\n\n| Task | Typical time |\n|---|---|\n| Collecting and checking stack data, emission rates and the plant layout | Half a day to two days |\n| Finding meteorological data, checking completeness and representativeness | Half a day to two days |\n| Setting up and running AERMET, checking its messages | Half a day to a day |\n| Writing the AERMOD control files, receptors and boundary | Half a day to a day |\n| Running the model for each pollutant and checking the output | A few hours |\n| Post-processing: tables, isopleths, wind rose, location maps | One to two days |\n| Cumulative assessment and comparison with the NAAQS | A few hours to a day |\n| Writing the report | One to three days |\n| Independent check and corrections | Half a day to a day |\n\nTerrain, buildings or many source types can double these figures. The model run itself — the only part the free software does for you — is the smallest item on the list.\n\n## Downloads to Avoid\n\nSearches for \"AERMOD free download\" also return unofficial websites offering bundled installers, old versions or \"free\" copies of commercial interfaces. Avoid them:\n\n- **Only download the EPA programs from the EPA.** Unofficial bundles can contain outdated versions with known errors, or malware.\n- **Check the version.** The EPA identifies each AERMOD release by a date code (year and day of year, such as 26135). A report should state the version used, and reviewers may ask why an older one was chosen.\n- **Do not use unlicensed copies of commercial software.** Apart from the legal and security risks, an unlicensed copy cannot be updated or supported, and a study produced with it is hard to defend if its provenance is ever questioned.\n- **Be wary of \"free online AERMOD\" sites** that do not say which model runs or provide the input and output files. If you cannot reproduce a result with the EPA programs, it should not appear in a submission.\n\n## What Paid Desktop Interfaces Add\n\nCommercial interfaces such as Lakes Environmental's AERMOD View and Trinity Consultants' BREEZE AERMOD exist because the free route is laborious. They do not replace the EPA model — they run it — but they add:\n\n- **A graphical interface** for sources, buildings and receptors, usually on a map or aerial image.\n- **Built-in pre-processors** for AERMET, AERMAP and BPIP-PRIME, with data import tools.\n- **Meteorological data handling**, from import helpers to purchased data sets, depending on the product and region.\n- **Visualisation**: isopleth maps, 3D views, receptor tables and exports to GIS formats.\n- **Project management**: saving, copying and comparing scenarios.\n- **Vendor support and training**.\n\nThey are typically licensed per user, as perpetual licences with annual maintenance or as subscriptions, often with optional modules. Prices vary by product, region, modules and number of seats, so the only reliable figure is a current quote from the vendor.\n\nA licence makes sense if you run many studies, need the full range of AERMOD's options (terrain, downwash, many source types, deposition), and have trained staff to use it. It does not, by itself, solve the two hardest problems: representative meteorology for your site and a report in the format your regulator expects. Those still depend on the user.\n\n## What Online AERMOD Software Changes\n\nOnline applications run the EPA programs on the provider's machine and handle much of the surrounding work automatically: meteorological data selection and processing, receptor grids, post-processing and a report. You enter the study in a browser and get results in minutes.\n\nThe trade-off is scope. An online tool exposes the options its designers built in; a study that needs something else — complex terrain, buildings, fugitive sources — may not fit. Our article [AERMOD online](/blog/aermod-online-software/) walks through a browser-based run and lists the eight checks that tell a trustworthy tool from a risky one.\n\n## Comparing the Four Routes\n\n| | Free EPA programs, done yourself | Desktop licence | Online AERMOD software | Modelling service |\n|---|---|---|---|---|\n| Software cost | None | Licence and maintenance | Per study or per account | Included in the study fee |\n| Your time per standard study | High | Medium | Low | Lowest: you provide inputs and review |\n| Skills needed | Modeller-level | Trained user | Understanding of the inputs | Understanding of the inputs |\n| Meteorological data | You find and process it | You find it; tools help process it | Selected and processed by the tool | Handled by the modeller |\n| Complex sites | Fully possible, with expertise | Fully supported | Depends on the tool | Fully supported |\n| Report | You write it | You assemble it | Generated in a fixed format | Written for your template |\n| Risk of an undetected error | Highest | Medium | Low for standard studies | Low, with independent QA |\n| Best for | Learning, research, occasional simple runs | Modelling teams with steady volume | Consultants and industries with standard stack studies | Complex, high-stakes or white-label studies |\n\nThe real cost comparison — staff time, data, rework and the price of a rejected study — is covered in our articles on [AERMOD modelling cost](/blog/aermod-modelling-cost/) and the [cost of air dispersion modelling in India](/blog/cost-of-air-dispersion-modelling-india/). The short version: for an organisation that runs a few standard studies a year, the free programs are rarely the cheapest option once time is counted, and a licence is rarely used enough to pay for itself.\n\n## Is a \"Free\" Study Good Enough for an Indian Submission?\n\nThe regulator does not care what the software cost. What a State Pollution Control Board or an Expert Appraisal Committee examines is:\n\n- **The model and its options** — the EPA AERMOD with regulatory defaults is accepted practice in Indian EIA studies.\n- **The inputs** — emission rates and stack parameters consistent with the project design and the consent conditions.\n- **The meteorology** — representative of the site, for the study period, with enough valid hours. For EIA studies, data from the site weather station during the baseline season is normally expected.\n- **The receptors** — fine enough to find the maximum, with sensitive locations reported.\n- **The cumulative assessment** — background from the baseline monitoring, added correctly, compared with the NAAQS 2009.\n- **The documentation** — enough to reproduce the run.\n\nA study done with the free programs, carefully, meets every one of these. So does one done with a desktop licence or online software. A study done carelessly fails, whatever it cost.\n\n## Where AERMOD Sits Among Free Dispersion Models\n\nAERMOD is not the only free model the EPA distributes, and choosing the right model matters more than the price of any interface.\n\n- **AERMOD** is the preferred model for near-field dispersion — typically up to about 50 km — from industrial point, area, volume and line sources, in flat and complex terrain. It is the default choice for Indian EIA and consent studies of stacks.\n- **CALPUFF** is a free puff model that follows emissions through spatially varying wind fields. It is used for longer distances, coastal and complex flows and some deposition studies, and is more demanding to set up. Our comparison of [AERMOD and CALPUFF](/blog/aermod-vs-calpuff/) explains when each fits.\n- **AERSCREEN** is the screening companion to AERMOD, described below.\n- **Specialised models** exist for particular settings, such as offshore sources; they are rarely needed for Indian industrial studies.\n\nChoosing a model because it is free, or because an interface happens to support it, is the wrong way round. Start from the question the study must answer — see [choosing an air dispersion model](/blog/choosing-an-air-dispersion-model/) — and then choose the software.\n\n## Other Free Tools Worth Knowing\n\n- **AERSCREEN** gives a conservative maximum for a single source using worst-case meteorology instead of hourly data. It is useful for screening — \"is this stack obviously fine?\" — and for checking the order of magnitude of a full AERMOD result. It is not a substitute for a full study in an EIA.\n- **QGIS**, a free GIS, can plot receptor results, draw isopleths and prepare location maps.\n- **Python** with free libraries (pandas for tables, matplotlib for plots, pyproj for coordinate conversion) is enough to post-process AERMOD plot files and automate repetitive studies.\n- **NASA POWER** provides free hourly meteorological data for any location through a public web service — useful, with caveats, where station data is unavailable.\n\n## Who Should Use the Free Route\n\nThe free EPA programs, used directly, are the right choice for some people:\n\n- **Students and researchers** learning how dispersion modelling works. Writing a control file by hand and reading the raw output teaches more than any interface.\n- **Modellers checking another tool.** Re-running an archived study with the EPA executables is the most direct verification there is.\n- **Teams automating many similar runs.** Scripts that write control files and parse plot files can run hundreds of scenarios that no interface would handle comfortably.\n- **Occasional simple studies by an experienced modeller**, where the time to prepare inputs is small and no maps or formatted report are needed.\n\nIt is rarely the right choice for an organisation that needs a few regulatory studies a year, on deadline, without a modeller on staff. The free software does not reduce the time spent on meteorology, post-processing and reporting — it only removes the licence fee.\n\n## Questions to Ask Before You Pay for Any AERMOD Software\n\nWhether you are considering a desktop licence or an online service, these questions cut through feature lists:\n\n1. **Which EPA programs does it run, and which versions?** It should run the unmodified EPA executables and print their versions in the output.\n2. **What does it do about meteorological data for my sites?** Ask specifically about data after August 2025, when NOAA's legacy ISD files stopped updating.\n3. **Does it check data completeness and tell me?** A tool that does not report the share of valid hours leaves you exposed on the most common review comment.\n4. **Can I get every input and output file?** Without them, nobody can reproduce or audit your study.\n5. **Does it handle my typical site?** Terrain, buildings, fugitive sources, many stacks — know which you need before comparing.\n6. **Does it produce the outputs my regulator expects?** For India: GLC tables with locations, isopleths, the cumulative assessment against the NAAQS 2009, and a report in the familiar structure.\n7. **What happens when a study does not fit?** Is there someone who can take it over, or are you on your own?\n8. **How is it priced over a year of my actual volume?** Compare the total, not the headline price: licence, maintenance, data, training and staff time.\n9. **Can I try it on my own project first?** A demo with a canned example shows the interface; a demo with your site shows whether it works for you.\n\n## Licensing and Responsibility: Two Things Often Missed\n\n**Free does not mean unsupported by evidence.** Using public software puts the burden of demonstrating correct use on the user. Keep the input and output files, the meteorological processing files and a record of every choice.\n\n**Paid does not mean responsible.** A licence buys a tool, not an answer. The study proponent and its consultant remain responsible for the inputs and the interpretation, whichever software ran the model.\n\n## What the Free AERMOD Studio Demo Includes\n\nWe built [AERMOD Studio](/services/aermod-software/) for organisations in the middle of the table above: they need standard stack studies done correctly and quickly, in a format Indian reviewers recognise, without running a modelling desk. It runs the unmodified EPA AERMOD and AERMET programs on our processing machine, selects and documents the meteorology automatically, handles the plant boundary and the background, and produces the report and the model archive.\n\nThe demo is free, and it is your study rather than a canned example:\n\n1. You send the site coordinates, the stacks with their emission rates, and the season to model — plus the boundary and baseline data if you have them.\n2. We run the study in AERMOD Studio.\n3. In a short online session we take you through the meteorology that was selected and why, the maximum GLCs, the isopleths, the receptor and NAAQS tables, and the report.\n4. You keep the demo report, watermarked \"DRAFT\" so it is not mistaken for a submission copy.\n\nIf you then want to use the software, we quote a standard nominal charge per study or for an account, depending on your volume. Studies the software does not cover yet — terrain, building downwash, area or fugitive sources — we run as a [modelling service](/services/aermod-air-dispersion-modelling/).\n\n## Frequently Asked Questions\n\n### Is AERMOD free to download?\n\nYes. The US EPA publishes AERMOD, AERMET, AERMAP, BPIP-PRIME and the related programs free of charge on its SCRAM website, with source code and user guides. There is no licence fee or registration.\n\n### Is AERMOD View free?\n\nNo. AERMOD View is a commercial interface from Lakes Environmental that runs the free EPA programs; it is sold under licence. The same is true of other commercial interfaces. Check the vendor's website for current terms and trial options.\n\n### Can I use the free EPA AERMOD for an Indian EIA?\n\nYes. The EPA programs are what every interface runs underneath. What matters for acceptance is correct inputs, representative and complete meteorology, an adequate receptor grid, a correct cumulative assessment against the NAAQS 2009, and documentation that lets the run be reproduced.\n\n### What is the hardest part of doing it yourself?\n\nMeteorology: finding a representative station, checking completeness for your period, and running AERMET with the right options. Since NOAA's legacy station files stopped updating in August 2025, finding surface data for recent periods has become harder still.\n\n### Is there a free trial of AERMOD software?\n\nMany commercial interfaces offer time-limited trial licences; check each vendor's website for current terms. A trial usually lets you explore the interface with sample data. The AERMOD Studio demo works differently: we run your own site and show you the actual results, meteorology and report for it, which tells you more about whether the software fits your work.\n\n### Does AERMOD run on Linux or Mac?\n\nThe EPA provides Windows executables and the Fortran source code. The source can be compiled with a Fortran compiler such as gfortran on Linux or macOS.\n\n### Is AERSCREEN enough for a consent application?\n\nAERSCREEN is a screening tool. It can show that a source is clearly acceptable under worst-case assumptions, but EIA studies in India are normally expected to use AERMOD with hourly meteorology for the study period.\n\n### What does the AERMOD Studio free demo include?\n\nOne study of your own site — your coordinates, stacks and season — run with the EPA programs, followed by an online walkthrough of the meteorology, results and report. You keep the watermarked draft report. There is no obligation to buy.\n\n### How much does AERMOD Studio cost after the demo?\n\nWe quote a standard nominal charge per study or for an account, depending on how many studies you run. There are no separate software licences or meteorological data subscriptions.\n\n---\n\n**See AERMOD Studio run your own site — the demo is free.** Send us the site coordinates, the stacks and the season you want to model; we run the study and take you through the meteorology, the isopleths and the report in a short online session. See [AERMOD Software (AERMOD Studio)](/services/aermod-software/), or if your study needs terrain, building downwash or area sources, our [AERMOD modelling service](/services/aermod-air-dispersion-modelling/). DS Technoverse is based in **Indore, Madhya Pradesh** and works with consultants and industries across India.","related":[{"slug":"common-aermod-mistakes","title":"10 Common AERMOD Modelling Mistakes That Fail Regulatory Review"},{"slug":"aermet-meteorological-data-preprocessing","title":"AERMET Explained: How Meteorological Data Is Prepared for AERMOD"},{"slug":"aermod-building-downwash-bpip","title":"AERMOD Building Downwash (BPIP-PRIME): A Practical Overview"},{"slug":"aermod-modelling-consultant-india","title":"AERMOD Modelling Consultant in India: What They Do and How to Hire One"}]}