Outdoor urban aerosols and their transport and fate indoors

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Title: Outdoor urban aerosols and their transport and fate indoors
Author: Mølgaard, Bjarke
Contributor: University of Helsinki, Faculty of Science, Department of Physics, Division of Atmospheric Sciences
Publisher: Helsingin yliopisto
Date: 2014-01-24
URI: http://urn.fi/URN:ISBN:978-952-5822-83-0
Thesis level: Doctoral dissertation (article-based)
Abstract: Epidemiological and toxicological studies have clearly shown that air pollution has adverse effects on human health. Exposure to air pollution mainly occurs in the urban and in the indoor environment. Fine particles form a diverse group of air pollutants, which is responsible for some of the health effects, and they originate from many outdoor and indoor sources. This thesis aims to support efforts for reduction of human exposure to fine particles by development and evaluation of an urban forecast model and by evaluation of an indoor aerosol model and of air cleaners. Measured particle number size distributions were utilised in all studies, and the urban studies additionally utilised meteorological data. The urban aerosol was investigated by using cluster analysis, and the urban particle number concentration forecast model was based on a regression model with an autoregressive structure on its error term. It was evaluated using particle number concentrations from five cities. The utility of a Multi-Compartment Size-resolved Indoor Aerosol Model (MC-SIAM) for estimating airflows in a building was evaluated by comparison with results from a tracer gas technique. The performance of five portable indoor air cleaners was evaluated by applying a simple aerosol model to data from chamber experiments. The urban concentration of particles smaller than 50 nm was found to depend on local sources, while for larger sizes distant sources may dominate the concentration. The forecast model was found to perform best for locations with a strong influence of local sources. The estimates obtained with the MC-SIAM of airflows between the indoors and outdoors were good for periods during which good agreement between the modelled and measured particle number size distributions was obtained. The indoor airflow estimates deviated somewhat due to a commonly used simplification. Portable air cleaners utilising fans and filters performed as expected, but an ion generator was ineffective for most particle sizes. The forecast model can give useful forecasts in its present form under certain conditions but further development is desired to make it more versatile. The MC-SIAM is a valuable tool for the study of indoor aerosols except in case of fluctuating airflows. Portable air cleaners are useful for improving indoor air quality, but not all models perform well.Pienhiukkaset ja muut ilmansaasteet voivat aiheuttaa monenlaisia sairauksia. Ilmansaasteita on sekä ulko-, että sisäilmassa. Osa sisätilojen pienhiukkasista tulee ulkoa, varsinkin kaupunkialueilla. Väitöstyössä tutkittiin Helsingin ulkoilman pienhiukkaspitoisuuksia ja saatiin selville, että pienimpien hiukkasten lähteet ovat paikallisia. Näiden hiukkasten halkaisija on < 50 nanometriä ja niiden tärkein lähde on autoliikenne. Isommat hiukkaset tulevat osittain kaupungin ulkopuolelta. Työssä kehitettiin pienhiukkaspitoisuuksien ennustusmalli, joka vaatii syöttötietoa sekä aikaisemmista pienhiukkasten pitoisuuksista, että liikenne- ja sääennusteista. Sen avulla voidaan ennustaa pienhiukkasten lukumääräpitoisuutta niiden mittauspisteillä. Malli toimii parhaiten kaupungeissa, joissa suurin osa hiukkasten lähteistä sijaitsee lähellä. Työssä testattiin lisäksi viittä sisäkäyttöön tarkoitettua ilmanpuhdistinta, jotka poistivat ilmasta pienhiukkasia joko suodattimien tai voimakkaan sähkökentän avulla. Koetuloksissamme suodattimilla toimivat ilmanpuhdistimet olivat tehokkaimpia.
Subject: physics
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