Ion Assisted Measurements of Trace Gases and Particle Growth

一种特殊设计的质谱仪被用来识别和测量大气中的离子。这些离子是带有正电荷或负电荷的单个大气气体分子。该仪器是经过数年的实验室工作开发出来的，能够从大气中提取浓度远低于万亿分之一的离子，并将它们注入质谱仪的真空室。用光谱仪测量离子的质量，可以对它们进行化学鉴定。一种常压流管，可向其中注入特定离子，用于测量微量大气物质，包括气相硫酸、甲磺酸和丙二酸、吡啶和氨。所有这些都被认为是可测量的，在清洁空气中的浓度低至万亿分之0.001。该技术的变体将用于搜索大型自然发生的离子簇，并研究由特定离子种类（如质子化吡啶或硝酸盐离子）形成或带电的簇。离子辅助测量将用于臭氧、二氧化硫、氮氧化物，可能还有OH自由基。这些离子测量的极端灵敏度为探测和测量迄今未被怀疑的自然或人为来源的大气微量气体提供了新的可能性，其中一些可能来自生物来源，例如吡啶。预计这些对大气离子性质的研究将有助于阐明大气中气体向粒子转化的分子细节。这意味着对水滴的成核和云的形成有了更好的理解。

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.