Chemical ionization of clusters formed from sulfuric acid and dimethylamine or diamines
Chemical ionization (CI) mass spectrometers are used to study atmospheric nucleation by detecting clusters produced by reactions of sulfuric acid and various basic gases. These instruments typically use nitrate to deprotonate and thus chemically ionize the clusters. In this study, we compare clu...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/12513/2016/acp-16-12513-2016.pdf |
| Summary: | Chemical ionization (CI) mass spectrometers are used to
study atmospheric nucleation by detecting clusters produced by reactions of
sulfuric acid and various basic gases. These instruments typically use
nitrate to deprotonate and thus chemically ionize the clusters. In this
study, we compare cluster concentrations measured using either nitrate or
acetate. Clusters were formed in a flow reactor from vapors of sulfuric acid
and dimethylamine, ethylene diamine, tetramethylethylene diamine, or
butanediamine (also known as putrescine). These comparisons show that
nitrate is unable to chemically ionize clusters with high base content. In
addition, we vary the ion–molecule reaction time to probe ion processes
which include proton-transfer, ion–molecule clustering, and decomposition of
ions. Ion decomposition upon deprotonation by acetate/nitrate was observed.
More studies are needed to quantify to what extent ion decomposition affects
observed cluster content and concentrations, especially those chemically
ionized with acetate since it deprotonates more types of clusters than
nitrate.<br><br>Model calculations of the neutral and ion cluster formation pathways are
also presented to better identify the cluster types that are not efficiently
deprotonated by nitrate. Comparison of model and measured clusters indicate
that sulfuric acid dimers with two diamines and sulfuric acid trimers with two
or more base molecules are not efficiently chemical ionized by nitrate. We
conclude that acetate CI provides better information on cluster abundancies
and their base content than nitrate CI. |
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| ISSN: | 1680-7316 1680-7324 |