Mass Spectrometry Study on Ions Generated by Low-Temperature Plasma Jet

The low-temperature plasma (LTP) jet is a potentially effective method to accelerate “ion-mediated nucleation” in the lower troposphere by providing lots of ions. In this article, besides the basic characteristics of helium-based LTP such as the current-voltage value and optical emission spectroscopy, the positive and negative ion densities away from the LTP jet were measured by the ion counter. The positive ion density was higher than negative ion density. The increasing applied voltage increased the ion density substantially. The mass spectrometry measurements indicate that for the positive ions, although LTP jet generated lots of ions such as He
⁺
, He
₂
⁺
, O
₂
⁺
, and N
₂
⁺
, the final dominant ions were hydronium ions and their water clusters H
₃
O
⁺
(H
₂
O)
_n
; for the negative ions, the dominant ions were OH
^-
, CO
₃
^-
, and NO
₃
^-
, and their water clusters. The production mechanism of these ions was also summarized. Finally, the larger flow rate was found to be able to enhance the generation of ions.