Chemical ionisation mass spectrometer for measurements of OH and Peroxy radical concentrations in moderately polluted atmospheres
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A new version of an atmospheric pressure chemical ionisation mass spectrometer has been developed for ground based in situ atmospheric measurements of OH and total peroxy (HO2 + organic peroxy) radicals. Based on the previously developed principle of chemical conversion of OH radicals to H2SO4 in reaction with SO2 and detection of H2SO4 using an ion molecule reaction with NO 3 ─ , the new instrument is equipped with a turbulent chemical conversion reactor allowing for measurements in moderately polluted atmosphere at NO concentrations up to several ppb. Unlike other similar devices, where the primary NO 3 ─ ions are produced using radioactive ion sources, the new instrument is equipped with a specially developed corona discharge ion source. According to laboratory measurements, the overall accuracy and detection limits are estimated to be, respectively, 25% and 2 × 105 molecule cm-3 for OH and 30% and 1 × 105 molecule cm-3 for HO2 at 10 min integration times. The detection limit for measurements of OH radicals under polluted conditions is 5 × 105 molecules cm-3 at 10 min integration times. Examples of ambient air measurements during a field campaign near Paris in July 2007 are presented demonstrating the capability of the new instrument, although with reduced performance due to the employment of non isotopic SO2.
KeywordsHydroxyl radical Peroxy radical Chemical ionisation mass spectrometer Atmospheric measurements
We thank Bernard Mège and Jean-Christophe Samaké for technical assistance and help in preparation of the field campaign. The development of the instrument has been supported by the “PRIMEQUAL 2” program of the Ministère de l’Aménagement du Territoire et de l’Environnement, the “BQR” programs of the Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) and Université Paris VI, funding from the Institut National des Sciences de l'Univers (INSU). The measurements in the simulation chamber of ICARE (former LCSR) (Orléans) were supported by the EU project EUROCHAMP (RII-CT-2004-505968).
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