Experimental Study on the Interference of Water Vapor on the Chemical Ionization of OH by Sulfur Hexafluoride Ion

Abstract

The interference of water vapor on the chemical ionization (CI) of hydroxyl radicals (OH) by sulfur hexafluoride ion (SF 6 -) was investigated using a flow tube system coupled to a high-pressure CI mass spectrometer. Water vapor, which is required to study heterogeneous reactions of OH under real tropospheric conditions, transforms the reagent ion SF ) and water molecules. An additional helium buffer flow introduced into the CI region reduced loss of the reagent ion and resulted in a partial recovery of OH peak intensities under humid conditions.

Experimental study on HCl uptake by MgCl2 and sea salt under humid conditions

“…An additional flow of He was used to prevent the formation of water clusters with SF 6 − in the chemical ionization region and thus to ensure sufficient CIMS sensitivity. 18,19 The SF 6 − ions entered a chamber differentially pumped by two turbo molecular pumps (Leybold 360CSV…”

“…The remainder of HCl from the heterogeneous reaction in the differential flow tube entered the chemical ionization region via a 1‐mm skimmer for ionization by the following fluoride ion transfer reaction from SF 6 − ions 16,17 that were produced by passing SF 6 (Matheson Tri Gas, 99.99%) diluted in N 2 through a 210 Po source (NRD): An additional flow of He was used to prevent the formation of water clusters with SF 6 − in the chemical ionization region and thus to ensure sufficient CIMS sensitivity 18,19 . The SF 6 − ions entered a chamber differentially pumped by two turbo molecular pumps (Leybold 360CSV and Seiko‐Seiki STP‐400) through a 0.5‐mm pinhole biased at −5 V. A series of ion optics focused the ions to maximize the detection with a quadrupole mass spectrometer.…”