A Investigation of Tropospheric Ions

Using a high pressure drift tube mass spectrometer, reduced mobility measurements of ions of atmospheric interest have been made as a function of temperature. Specifically, the mobilities of NO(,2)('-), NO(,3)('-), CO(,3)('-), Br(' -), Cl('-), NH(,4)('+), NO(,2)('-)(,(.)) H(,2)O, NO(,3)(' -)(,(.)) H(,2)O, CO(,3)('-)(.) H(,2)O, and CO(,4)('-)(.) H(,2)O in nitrogen and NO(,2)('-), NO(,3)('-), O(,2)('+), CO(,3)('-), and CO(,4)('-) in oxygen have been measured. These ions have been observed in the stratosphere and above. Mass identification of ions in the atmosphere has beed made only in the atmosphere and above, since, at these altitudes, the neutral gas density is considerably lower and the ion concentrations are generally higher than at ground level. For this thesis an apparatus which is capable of directly sampling ions in the troposphere has been developed. This device can mass analyze and detect ions at concentrations as low as 100 to 1000 ions per cm('3) at atmospheric pressures (760 torr). This type of apparatus can contribute considerably to both our understanding of ion chemistry and to our knowledge of certain trace neutral concentrations in the troposphere. Using the apparatus, naturally occurring positive and negative ions in the troposphere have been mass identified at Sapelo Island, Georgia, and Mt. Evans, Colorado. These measurements were made at ground level under a variety of weather conditions. Over the course of the experiment, positive ions were seen at masses 54, 60, 80, and 94 AMU. Mass 54 AMU is believed to be NH(,4)('+)(.) 2(H(,2)O). In the negative ion spectrum, ions were observed at masses 62 and 125 AMU and are believed to be NO(,3)('-) and NO(,3)(' -)(.) (HNO(,3)). Several ions that appear to be water clusters of the above ions were also observed. These are the first measurements of the mass identity (one AMU resolution) of naturally occurring ions in the troposphere. Ions that were artificially produced were also studied and compared to the much longer lived natural ions.