Abstract. The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO₃^– ions with H₂SO₄. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (americium-241) ion source which has been used previously. The results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of 1 min it is ~6 × 10⁴ molecule cm⁻³ of H₂SO₄. In addition, only a small cross-sensitivity to SO₂ has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO₂ is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H₂SO₄ concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H₂SO₄ is measured by CIMS.