Chen, L.-W.A., Lowenthal, D. H., Watson, J. G., Koracin, D. R., Kumar, N., Knipping, E. M., Wheeler, N., Craig, K., Reid, S. (2010). Toward Effective Source Apportionment Using Positive Matrix Factorization: Experiments with Simulated PM2.5 Data, J. Air Waste Manage. Assoc., 60 (1), 43-54, 10.3155/1047-3289.60.1.43