Torsion cycle class maps in codimension two of arithmetic schemes

We study the cycle class map from the Chow group in codimension 2 of an arithmetic scheme X (i.e., a regular proper flat scheme over an algebraic integer ring) to its new cohomology theory defined by a candidate, introduced by the second author, of the conjectural étale motivic complex with finite coefficients of Beilinson-Lichtenbaum. The injectivity of its torsion part is deduced from the finiteness of an unramified cohomology group of X. This finiteness is then deduced from a well-known conjecture in arithmetic geometry. As a consequence we obtain an injectivity result under the assumption H(V,OV ) = 0, where V denotes the generic fiber of X.