The EPA Unmix model “unmixes” the concentrations of chemical species measured in the ambient air to identify the contributing sources. Chemical profiles of the sources are not required, but instead are generated internally from the ambient data by Unmix, using a mathematical formulation based on a form of factor analysis.
Quoted from: https://www.epa.gov/air-research/unmix-60-model-environmental-data-analyses
EPA’s Unmix Model is a mathematical receptor model developed by EPA scientists that provides scientific support for the development and review of the air and water quality standards, exposure research, and environmental forensics. Unmix can analyze a wide range of environmental sample data: sediments, wet deposition, surface water, ambient air, and indoor air. EPA’s Unmix model reduces the large number of variables in complex analytical data sets to combinations of species called source types and source contributions. The source types are identified by comparing them to measured profiles. Source contributions are used to determine how much each source contributed to a sample.
Unmix quantifies the sources of contaminants contributing to sediment, water and air samples based on chemically speciated data. Unmix determines the number of sources impacting the samples based on user provided data. The model is free of charge, and does not require a license or other software to use.
Scientists and engineers who generate or analyze speciated sample data and want to quantify the sources contributing to environmental samples can use Unmix 6.0. In addition, chemists can use Unmix 6.0 to evaluate instrument data.
Users of EPA’s Unmix model provide files of sample species concentrations, which the model uses to calculate the number of source types, profiles, relative contributions, and a time-series of contributions. Unmix does not make any assumptions as to the number and composition of the sources, relying instead on the correlations of the observed species. The species concentrations are apportioned by a principal components analysis using constraints to assure non-negative and realistic sources compositions and contributions. The Unmix model software uses graphical user interfaces that ease data input, generation, evaluation and exporting of results. Algorithms used in the Unmix model have been peer reviewed by leading air quality management scientists.
Unmix 6.0 works on Windows 2000, Windows XP, and Windows Vista. The computer should have at least a 2.0 GHz processor and 512 MB of memory. Microsoft Excel is required for saving and exporting output. Unmix may not be entirely compatible with newer versions of Windows (e.g. Windows 7, Windows 8).
The EPA Unmix 6.0 Fundamentals & User Guide provides references and details on how to use Unmix.
Unmix 6.0 Fundamentals & User Guide
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