Hygroscopic Properties of Atmospheric Aerosol Particles in Various Environments

Sammanfattning: Atmospheric aerosol particles affect our living environment in many ways. Their effects are influenced by the interaction between the aerosol particles and the ubiquitous water vapour. The number-size distribution is a primary important parameter for aerosol particles and can be measured using the differential mobility particle sizer (DMPS). Programs have been developed to invert DMPS measurement data to actual aerosol number-size distributions and further fit it to multimodal lognormal distributions. The hygroscopic tandem differential mobility analyser (H-TDMA) is the essential instrument used in studying aerosol hygroscopic properties. The H-TDMA has been developed continuously regarding measurement control and data acquisition system, as well as in the subsequent data interpretation and quality assurance. Four field experiments have been performed in this work in order to study hygroscopic properties of atmospheric aerosol particles. In a polluted continental environment, the aerosol hygroscopic growth was observed in connection with a ground-based cloud experiment at Great Dun Fell, in northern England in 1995. In a remote marine background environment, ship-based hygroscopic measurements were carried out during the Arctic Ocean Expedition in 1996. In a moderately polluted marine environment, six H-TDMA instruments were operated simultaneously by four research groups at five sites in the subtropical north-eastern Atlantic, during the second Aerosol Characterization Experiment in 1997. More recently, hygroscopic growth measurements were performed in the Amazon rain forest, a remote tropical continental site, during the first Cooperative LBA (Large-scale Biosphere-Atmosphere) Airborne Regional Experiment in 1998. The measured hygroscopic growth data can be used in an aerosol hygroscopic growth model, together with measurements of aerosol size distributions and chemical composition. Closure studies were performed to verify whether the independent measurements were consistent, and to what extent the model was able to describe aerosol hygroscopic growth and aerosol-cloud interaction. The sub-micrometer atmospheric aerosol particles observed by several research groups in various environments exhibit a modal hygroscopic structure, indicating that atmospheric aerosol particles are, to some extent, externally mixed regarding their hygroscopic properties and hence also chemically.