Ion Assisted Measurements of Trace Gases and Particle Growth

点击翻译按钮获取中文摘要

A mass spectrometer of special design is used to identify and measure ions in the atmosphere. These ions are individual molecules of atmospheric gases bearing either positive or negative electrical charges. The apparatus, developed over several years of laboratory work, is capable of extracting from the atmosphere ions existing in concentrations well below one part in a trillion, and injecting them into the vacuum chamber of a mass spectrometer. Measurement of the masses of the ions by the spectrometer permits their chemical identification. An atmospheric-pressure flow tube into which specific ions can be injected is used for the measurement of trace atmospheric species, including gas-phase sulfuric, methanesulfonic and malonic acids, pyridine, and ammonia, all of which are believed to be measurable at concentrations as low as 0.001 part per trillion in clean air. Variants of the technique will be used to search for large naturally occurring ion clusters, and to study clusters formed, or charged, by specific ion species such as protonated pyridine or the nitrate ion. Ion-assisted measurements will be made of ozone, sulfur dioxide, nitrogen oxides, and possibly of the OH free radical. The extreme sensitivity of these ion measurements opens up new possibilities of detecting, and measuring hitherto unsuspected low levels of atmospheric trace gases of natural or man-made origin, some of which may come from biological sources, e.g., pyridine. It is expected that these studies of the properties of atmospheric ions will help to clarify the molecular details of the conversions of gases to particles in the atmosphere. Implied in this is a better understanding of the nucleation of water droplets, and this of cloud formation.