Experimental studies of the formation of cluster ions formed by corona discharge in an atmosphere containing SO2, NH3, and H2O

• We observe charged clusters containing more than 100 water molecules.
• Only clusters with a maximum of two sulfuric acid molecules were observed.
• The negative ion HSO5− was found to be contaminated by O2−(HNO3)(H2O) ions.
• An unidentified ion with m/z = 232 capable of attaching H2O-molecules was observed.

We report on studies of ion-induced nucleation in a corona discharge taking place in an atmosphere containing SO2, NH3, and H2O at standard temperature and pressure. Positive ions such as H3O+(H2O)n, NH4+(H2O)n, and H+(H2SO4)(H2O)n and negative ions such as HSO5−(H2O)n, SO4−(H2O)n, HSO4−(H2O)n and NO3−(H2O)n have been recorded. Large values of n (>100) were observed and the experiment indicates the existence of even larger water clusters. In contrast, only clusters with a maximum of 2 sulfuric acid molecules were observed. Fragmentation studies also revealed that the negative ion HSO5−, which has been observed in many studies, in our experiments is contaminated by O2−(HNO3)(H2O) ions, and this may also have been the case in other experiments. Finally an ion with m/z = 232 (where m is the cluster mass in amu and z is the charge state), capable of attaching H2O-molecules was observed and studied by fragmentation.

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