Field measurements of hygroscopic properties and state of mixing of nucleation mode particles

[摘要] An Ultrafine Tandem Differential Mobility Analyser(UF-TDMA) has been used in several field campaigns over the last few years. Theinvestigations were focused on the origin and properties of nucleation event aerosols, which are observed frequently invarious environments. This paper gives a summary of the results of 10 nm and20 nm particle hygroscopic properties from different measurement sites: an urban site, an urbanbackground site and a forest site in Finland and a coastal site in western Ireland. The data can be classified in four hygroscopicgrowth classes: hydrofobic, less-hygroscopic, more-hygroscopic and sea-salt. Similar classification has been earlier presented forAitken and accumulation mode particles. In urban air, the summertime 10 nm particles showed varying less-hygroscopicgrowth behaviour, while winter time 10 nm and 20 nm particles were externally mixed with two differenthygroscopic growth modes. The forest measurements revealed diurnal behaviour of hygroscopic growth, with high growth factors at daytime and lower during night. The urban background particles had growth behaviour similar to the urban and forest measurement sitesdepending on the origin of the observed particles. The coastal measurements were strongly affected by air mass history. Both10 nm and 20 nm particles were hygroscopic in marine background air. The10 nm particles produced during clean nucleation burst periods were hydrofobic. Diurnal variationand higher growth factors of 10 nm particles were observed in air affected by other source regions. External mixing wasoccasionally observed at all the sites, but incidents with more than two growth modes were extremely rare.

[学科分类] 大气科学