<p><strong>Abstract.</strong> We present a chemical ionization quadrupole mass spectrometer (CI-QMS) with a radio-frequency (RF) discharge ion source through <span class="inline-formula">N₂∕CH₃I</span> as a source of primary ions. In addition to the expected detection of PAN, peracetic acid (PAA) and <span class="inline-formula">ClNO₂</span> through well-established ion–molecule reactions with <span class="inline-formula">I⁻</span> and its water

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... r, the instrument is also sensitive to <span class="inline-formula">SO₂</span>, HCl and acetic acid (<span class="inline-formula">CH₃C(O)OH</span>) through additional ion chemistry unique to our ion source. We present ionization schemes for detection of <span class="inline-formula">SO₂</span>, HCl and acetic acid along with illustrative datasets from three different field campaigns underlining the potential of the CI-QMS with an RF discharge ion source as an alternative to <span class="inline-formula">²¹⁰Po</span>. The additional sensitivity to <span class="inline-formula">SO₂</span> and HCl makes the CI-QMS suitable for investigating the role of sulfur and chlorine chemistry in the polluted marine and coastal boundary layer.</p>