We obtain necessary and sufficient conditions for the existence of positive solutions (not necessarily bounded) which satisfy global pointwise estimates of Brezis–Kamin type given in terms of Wolff potentials. Similar problems with the fractional Laplacian ass="imgLazyJSB inlineImage" height="15" width="62" alt="View the MathML source" style="margin-top: -5px; vertical-align: middle" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0362546X16301791-si10.gif">a>