SoFi - SourceFinder


SoFi (SourceFinder) is a program developed at PSI that facilitates source apportionment analysis based on PMF/Me-2 on any ambient data. SoFi comes in two versions, the standard version (freeware) and the Pro version (lisence-based).

SoFi standard

SoFi is intended to facilitate the source apportionment based on Positive Matrix Factorization (PMF) and the multilinear engine (ME-2) of measured ambient data. The software was developed for analysis of ACSM data. However, the algorithm can be applied to any kind of data and therefore, it can be distributed to all ME-2 / PMF users dealing in general with any kind of measurements.

The standard version allows to explore and pretreat the PMF input, which includes, but is not limited to, selection of the effective PMF input (exclusion of time points or variables), down-weighting of variables and use a robust threshold. With the standard version it is possible to run unconstrained PMF as well as constrained PMF with either the a-value or the f-peak approach. The preparation of the external data can be easily done in SoFi. SoFi offers a very user-friendly PMF data analysis. With a few mous-clicks, the user can plot time series, profiles, contributions, correlations with variables and externals and much more. More information can be found in the manual.

The standard version can be downloaded here. SoFi is based on the ME-2 engine.

SoFi Pro

The SoFi Pro add-on will allow for following extra features:
  • bootstrap application on PMF input for the assessment of the statistical error and subsequent analysis using the dynamic criteria-based feature
  • Inspection and selection of PMF runs based on user-defined proxies/tracers (dynamic criteria-based feature)
  • average over several PMF runs and visual inspection of the solution (statistics on average)
  • user-based PMF sub-window moves over the entire PMF input allowing to model changing factor profiles (rolling approach). Especially relevant for long-term SA studies with profiles known to vary over time
  • manual and automated application of the C-value, when combining data from two and more instruments and subsequent graphical support when exploring these solutions
  • hourly and/or daily average in SoFi for externals, PMF input and solution
  • variables and/or time points can be classified for further analysis, e.g. PMF with data from various stations at the same time or various size-fractions
  • saving and loading user-specific PMF input and constraints or user-defined criteria, graphical support for the quantification of the PMF error, statistics on the a value constraints.
For more information and the costs, please contact Francesco Canonaco (

Technical Description

SoFi requires Igor 6. It has not been tested for Igor 7 yet and it can also not be guaranteed that it will run error-free with older Igor versions.
The manual for SoFi standard can be found here.

ME-2 engine

SoFi is based on the ME-2 engine. The download here includes the full engine but not the license key. For the key, please contact Pentii Paatero ( The key has to be saved in the ME-2 engine folder: \ME2_engine\.


More than 25 papers based on SoFi calculations have been published.

SoFi, an IGOR-based interface for the efficient use of the generalized multilinear engine (ME-2) for the source apportionment: ME-2 application to aerosol mass spectrometer data Canonaco F, Crippa M, Slowik JG, Baltensperger U, Prévôt ASH, ATMOSPHERIC MEASUREMENT TECHNIQUES 6, 3649 (2013). DOI: 10.5194/amt-6-3649-2013
Seasonal differences in oxygenated organic aerosol composition: implications for emissions sources and factor analysis Canonaco F, Slowik JG, Baltensperger U, Prévôt ASH, ATMOSPHERIC CHEMISTRY AND PHYSICS 15, 6993 (2015). DOI: 10.5194/acp-15-6993-2015