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• 作者：Wilhelm ; Stefan ; Eichkorn ; Sven ; Wiedner ; Dirk ; Pirjola ; Liisa ; Arnold ; Frank
• 关键词：Positive and negative ions ; Sulphuric acid mole fraction ; Growth of ions ; Homogeneous nucleation ; Ion-induced nucleation
• 刊名：Atmospheric Environment
• 出版年：2004
• 出版时间：April, 2004
• 年：2004
• 卷：38
• 期：12
• 页码：1735-1744
• 全文大小：315 K

文摘

Here we report on laboratory investigations of mixed cluster ions composed of sulphuric acid and water molecules HSO₄⁻(H₂SO₄)_a(H₂O)_w and H⁺(H₂SO₄)_a(H₂O)_w. Such ions have potentially an important role in atmospheric H₂SO₄/H₂O aerosol formation via ion-induced nucleation. The investigations were made using a flow reactor equipped with two ion mass spectrometers which had either a high mass resolution but a relatively small mass range (0–750amu) or a low mass resolution but a large mass range (0–10000amu). Our experiments led to the following major findings: (a) Both negative and positive cluster ions take up H₂SO₄ molecules very efficiently. (b) For negative ions the sulphuric acid mole fraction is initially large, but as the ions grow, it rapidly approaches the value expected for neutral clusters. (c) For positive ions the sulphuric acid mole fraction is initially small, but as the ions grow, it rapidly increases and approaches the value expected for neutral clusters. (d) The measurements indicate that thermal detachment of sulphuric acid molecules from the cluster ions is important and strongly limits ion growth. The thermal detachment of sulphuric acid molecules is more efficient for positive ions compared to negative ions. Our experiments have interesting implications for ion-induced nucleation of H₂SO₄/H₂O in the atmosphere which are addressed.