Abstract
The interference of water vapor on the chemical ionization (CI) of hydroxyl radicals (OH) by sulfur hexafluoride ion (SF6-) 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 SF6- into SF4O-and F-(HF)n, resulting in a substantial loss in CI sensitivity. Therefore, under humid conditions, peaks corresponding to OH are drastically diminished, while those corresponding to OH-water complex ions ([OH(H2O)n]-) are enhanced. [OH(H2O)3]- was observed as the major OH species. The obsercation of [OH(H2O)n]- by isolating humid conditions to the CI region and preliminary ab initio calculations suggested that [OH(H2O)n]- ions were produced from reactions between OH ions (OH-) 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.
Highlights
The heterogeneous reactions of hydroxyl radicals (OH) occur on the surface of various atmospheric aerosols and have been studied to explain discrepancies between field measurements and theoretical values based on atmospheric modeling
This paper describes the use of a flow tube system coupled to a Chemical ionization mass spectrometry (CIMS) to explore the interactions among water molecules, reagent ions (SF6-), and/or OH radicals that reduce CIMS sensitivity
SF4O- can act as a reagent ion, the degree of chemical ionization (CI) was lowered through significant losses of both SF6- and SF4O
Summary
The heterogeneous reactions of hydroxyl radicals (OH) occur on the surface of various atmospheric aerosols and have been studied to explain discrepancies between field measurements and theoretical values based on atmospheric modeling. Abstract: The interference of water vapor on the chemical ionization (CI) of hydroxyl radicals (OH) by sulfur hexafluoride ion (SF6-) was investigated using a flow tube system coupled to a high-pressure CI mass spectrometer. The obsercation of [OH(H2O)n]- by isolating humid conditions to the CI region and preliminary ab initio calculations suggested that [OH(H2O)n]- ions were produced from reactions between OH ions (OH-) and water molecules.
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