On measurements of formation, growth, hygroscopicity, and volatility of atmospheric ultrafine particles

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http://urn.fi/URN:ISBN:952-5027-75-9
Title: On measurements of formation, growth, hygroscopicity, and volatility of atmospheric ultrafine particles
Author: Petäjä, Tuukka
Contributor: University of Helsinki, Faculty of Science, Department of Physical Sciences, Division of Atmospheric Sciences
Thesis level: Doctoral dissertation (article-based)
Abstract: Atmospheric aerosol particles affect the global climate as well as human health. In this thesis, formation of nanometer sized atmospheric aerosol particles and their subsequent growth was observed to occur all around the world. Typical formation rate of 3 nm particles at varied from 0.01 to 10 cm-3s-1. One order of magnitude higher formation rates were detected in urban environment. Highest formation rates up to 105 cm-3s-1 were detected in coastal areas and in industrial pollution plumes. Subsequent growth rates varied from 0.01 to 20 nm h-1. Smallest growth rates were observed in polar areas and the largest in the polluted urban environment. This was probably due to competition between growth by condensation and loss by coagulation. Observed growth rates were used in the calculation of a proxy condensable vapour concentration and its source rate in vastly different environments from pristine Antarctica to polluted India. Estimated concentrations varied only 2 orders of magnitude, but the source rates for the vapours varied up to 4 orders of magnitude. Highest source rates were in New Delhi and lowest were in the Antarctica. Indirect methods were applied to study the growth of freshly formed particles in the atmosphere. Also a newly developed Water Condensation Particle Counter, TSI 3785, was found to be a potential candidate to detect water solubility and thus indirectly composition of atmospheric ultra-fine particles. Based on indirect methods, the relative roles of sulphuric acid, non-volatile material and coagulation were investigated in rural Melpitz, Germany. Condensation of non-volatile material explained 20-40% and sulphuric acid the most of the remaining growth up to a point, when nucleation mode reached 10 to 20 nm in diameter. Coagulation contributed typically less than 5%. Furthermore, hygroscopicity measurements were applied to detect the contribution of water soluble and insoluble components in Athens. During more polluted days, the water soluble components contributed more to the growth. During less anthropogenic influence, non-soluble compounds explained a larger fraction of the growth. In addition, long range transport to a measurement station in Finland in a relatively polluted air mass was found to affect the hygroscopicity of the particles. This aging could have implications to cloud formation far away from the pollution sources.Hengittämässämme ilmassa on koko ajan pieniä kiinteitä tai nestemäisiä aerosolihiukkasia, jotka ovat liian pieniä pudotakseen maahan maan vetovoiman vaikutuksesta. Esimerkiksi pölyhitunen on aerosolihiukkanen. Yleisesti aerosolihiukkaset esimerkiksi heikentävät näkyvyyttä ja aiheuttavat hengityselin- ja sydänsairauksia. Lisäksi ne vaikuttavat koko maapallon ilmastoon, koska pilvet muodostuvat aerosolihiukkasten päälle. Ilmakehään aerosolihiukkaset joutuvat esimerkiksi tuulen nostaessa ilmaan aavikon hiekkaa, meren pärskeistä tai erilaisten kaasujen tiivistyessä. Väitöskirjassani tutkin hyvin pienten (halkaisijaltaan alle 100 nm, 1 nanometri on miljoonasosa millimetristä) aerosolihiukkasten muodostumista, kasvua ja ominaisuuksia. Väitöskirjassa kokosin yhteen viimeisten vuosikymmenien aikana tehdyt havainnot eri puolilta maapalloa. Yli sadassa tutkimuksessa havaittiin, että uusia aerosolihiukkasia muodostuu ilmakehässä kaikkialla: esimerkiksi Lapissa, Keski-Euroopassa, saastuneessa New Delhissä ja Antarktiksella. Tarkkaa muodostumismekanismia ei vielä tiedetä. Kaasuista muodostuneet hiukkaset ovat kooltaan niin pieniä, että niiden kemiallista koostumusta on hyvin vaikea mitata. Tässä työssä tarkkailtiin uusien, juuri muodostuneitten hiukkasten ominaisuuksien muutoksia, joka kertoi hiukkasten kemiallisen koostumuksen muutoksista. Mittaukset tehtiin Suomessa, Saksassa, Kreikassa ja Ranskassa. Saastuneessa ilmassa muodostuneitten uusien hiukkasten ominaisuudet poikkesivat puhtaassa ilmassa muodostuneista hiukkasista. Tämä voi puolestaan vaikuttaa esimerkiksi pilvien muodostumiseen ja sateen alueelliseen jakautumiseen.
URI: URN:ISBN:952-5027-75-9
http://hdl.handle.net/10138/23221
Date: 2006-11-11
Subject: fysiikka
Rights: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.


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