To compare the effect of nitrate anions on the surface tension increments of aqueous solutions with that of halide anions, the surface tension of aqueous solutions of lithium nitrate, sodium nitrate, and potassium nitrate was measured as a function of temperature and concentration. It is shown that the surface tension of aqueous alkali metal nitrate solutions is determined primarily by the kinds of anions, since the surface tension increments of these nitrates were of the same magnitude. The importance of the electrical double layer at the surface is discussed in relation to these surface tension increments. (c) 2007 Elsevier Inc. All rights reserved.