Evidence for a chemically differentiated outflow in Mrk 231 J. E. Lindberg, S. Aalto, S. Muller, I. Martí-Vidal, N. Falstad, F. Costagliola, C. Henkel, P. van der Werf, S. García-Burillo and E. González-Alfonso A&A, 587 (2016) A15 Published online: 12 February 2016 DOI: 10.1051/0004-6361/201527457