Wolf, Christian2015-03-272015-03-270035-8711http://hdl.handle.net/1885/13072We investigate reddening by Milky Way dust in the low-extinction regime of E(B − V) < 0.15. Using over 50 000 QSOs at 0.5 < z < 2.5 from the Sloan Digital Sky Survey (SDSS) data release 7 (DR7) QSO Catalogue, we probe the residual SDSS colours after dereddening and correcting for the known spectroscopic redshifts. We find that the extinction vector of Schlafly & Finkbeiner is a better fit to the data than that used by Schlegel et al. (SFD). There is evidence for a non-linearity in the SFD reddening map, which is similarly present in the V1.2 map of the Planck Collaboration. This non-linearity is similarly seen when galaxies or stars are used as probes of the SFD map.http://www.sherpa.ac.uk/romeo/issn/0035-8711/..."Publisher's version/PDF may be used, Author's Post-print and Publisher's version/PDF on Institutional repositories or Central repositories, Set phrase to accompany archived copy (see policy)" from SHERPA/RoMEO site (as at 276/03/15) This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.surveysdustextinctionISM: generalGalaxy: generalquasars: general2014-11-0610.1093/mnras/stu20692015-12-08