Ilmakehän hiukkasmuodostustapahtumien analyysi

Atmospheric aerosol particle formation events can be a significant source for tropospheric aerosols and thus influence the radiative properties and cloud cover of the atmosphere. This thesis investigates the analysis of aerosol size distribution data containing particle formation events, describes the methodology of the analysis and presents time series data measured inside the Boreal forest. This thesis presents a methodology to identify regional-scale particle formation, and to derive the basic characteristics such as growth and formation rates. The methodology can also be used to estimate concentration and source rates of the vapour causing particle growth. Particle formation was found to occur frequently in the boreal forest area over areas covering up to hundreds of kilometers. Particle formation rates of boreal events were found to be of the order of 0.01-5 cm^-3 s^-1, while the nucleation rates of 1 nm particles can be a few orders of magnitude higher. The growth rates of over 3 nm sized particles were of the order of a few nanometers per hour. The vapor concentration needed to sustain such growth is of the order of 10^7--10^8 cm^-3, approximately one order of magnitude higher than sulphuric acid concentrations found in the atmosphere. Therefore, one has to assume that other vapours, such as organics, have a key role in growing newborn particles to sizes where they can become climatically active. Formation event occurrence shows a clear annual variation with peaks in summer and autumns. This variation is similar to the variation exhibited the obtained formation rates of particles. The growth rate, on the other hand, reaches its highest values during summer. This difference in the annual behavior, and the fact that no coupling between the growth and formation process could be identified, suggest that these processes might be different ones, and that both are needed for a particle formation burst to be observed.Ilmakehän pienhiukkaset vaikuttavat auringon säteilyn kulkuun ilmakehässä sekä pilvipisaroiden syntyyn ja sitä kautta pilvipeitteeseen ja sadantaan. Kymmenen viime vuoden aikana tehdyissä mittauksissa on havaittu suuri määrä pienhiukkasten muodostumisepisodeja. Näissä episodeissa alailmakehän kaasuista syntyy suuri määrä uusia pienhiukkasia, jotka ovat halkaisijaltaan vain muutamia nanometrejä. Episodin aikana näihin hiukkasiin tiivistyy muita höyryjä, jotka kasvattavat hiukkasten kokoa aina satoihin nanometreihin, jolloin ne pystyvät toimimaan pilvien tiivistymisytiminä. Tässä väitöskirjatyössä on kehitetty menetelmiä näiden hiukkasmuodostusepisodien löytämiseen ja luokitteluun hiukkasten kokojakaumien perusteella. Lisäksi on kehitetty menetelmiä joilla datasta lasketaan hiukkasten muodostumisen ja kasvun voimakkuutta. Kehitettyjä menetelmiä on sovellettu pääosin Suomen metsäalueilla mitattuihin hiukkasmittaussarjoihin. Tutkimuksessa havaittiin, että pohjoisessa havumetsässä hiukkasmuodostusta taphtuu verrattain usein, keskimäärin joka neljäntenä päivänä, todennäköisimmin aurinkoisina päivinä ja silloin, kun taustahiukkasten määrä on alhainen. Hiukkasmuodostus on yleisintä keväisin ja syksyisin, kun taas talvella se on harvinaista. Hiukkasten kasvu sen sijaan on voimakkainta kesäisin, ja on todennäköistä, että rikkihapon lisäksi havupuiden emittoimat orgaaniset yhdisteet ovat tärkeässä osa kasvuprosessia

Effect of a deflector on deposition of particles with different diameters in a rib-roughened channel

A particulate flow in a rib-roughened channel is investigated using LRR model and a Lagrangian method. A deflector is placed in the channel to examine its effect on the deposition rate. The results show that a deflector increases the deposition rate with different diameter sizes by increasing the interaction between particles and lower wall. Particles with 50 μm diameter size have a high response time, hence when their path is changed toward the lower wall, they moved near the rough elements until they leave the channel. This behavior increases deposition velocity with this diameter size by 148.36%. For particles with 10 μm diameter size, it is found that deposition velocity increases by 24.71% due to their low response time. This study shows that while a deflector increases the particle deposition rate, it can cause pressure drop due to flow blockage.publishedVersionPeer reviewe

A source-orientated approach for estimating daytime concentrations of biogenic volatile organic compounds in an upper layer of a boreal forest canopy

Peer reviewe

NanoMap : Geographical mapping of atmospheric new-particle formation through analysis of particle number size distribution and trajectory data

Particle number size distributions at various field sites are used to identify atmospheric new-particle formation (NPF) event days. However, the spatial distribution of regionally extensive events is unknown. To remedy this situation, the NanoMap method has been developed to enable the estimation of where NPF occurs within 500 km from any field station using as input size distribution and meteorological trajectories only. Also, the horizontal extension of NPF can be determined. An open-source program to run NanoMap is available on the internet. NanoMap has been developed using as an example the Finnish field site at Hyytiala. It shows that there are frequent NPF events over the Baltic Sea, but not as frequent as over Finland for certain wind directions; hence NanoMap is able to pinpoint areas with a low or high occurrence of NPF events. The method should be applicable to almost any field site.Peer reviewe

Trajectory-based source area analysis of atmospheric fine particles, SO2, NOx and O3 for the SMEAR II station in Finland in 1996–2008

Non peer reviewe

Trends in atmospheric new-particle formation : 16 years of observations in a boreal-forest environment

Peer reviewe

Long-range transport of biomass burning smoke to Finland in 2006

Non peer reviewe

Monoterpene pollution episodes in a forest environment : indication of anthropogenic origin and association with aerosol particles

We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol