PROBLEM TO BE SOLVED: To provide a compact ion detection device capable of quickly and easily performing mass analysis under atmospheric pressure.SOLUTION: An ion detection device features an electrode arrangement and electrode holding style, which enable high-sensitivity detection of water clusters in the outdoor air by separating ions by means of a method different from those with conventional techniques, the method comprising having an ion detection portion of the device operate under atmospheric pressure to use, as force exerted on ions, not only electric field force but also air resistance, buoyant force, and gravity force, which naturally act thereon when the device is operated under atmospheric pressure.SELECTED DRAWING: Figure 1
