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

The behaviour of charged particles (ions) during new particle formation events in urban Leipzig, Germany

Air ions are electrically charged particles in air. They are ubiquitous in the natural environment and affect the Earth's radiation budget by accelerating the formation and growth of new aerosol particles. Despite this, few datasets exist exploring these effects in the urban environment. A neutral cluster and air ion spectrometer was deployed in Leipzig, Germany, to measure the number size distribution of charged particles from 0.8 to 42 nm, between 27 July and 25 August 2022. Following previous analyses, charged particles were classified into small (0.8-1.6 nm), intermediate (1.6-7.5 nm), and large (7.5-22 nm) fractions by mass diameter, and their mean concentrations (sum of positive and negative polarities) during the campaign were 405, 71.6, and 415 cm-3, respectively. The largest peaks in intermediate and large ions were explained by new particle formation (NPF), with intermediate ions correlating well with sulfuric acid dimer. Smaller morning and evening peaks were coincident with black carbon concentrations and attributed to primary emissions. NPF events, observed on 30 % of days, coincided with intense solar radiation and elevated sulfuric acid dimer. Small charged particles were primarily associated with radioactive decay and highest during the early hours, and they are unrelated to primary emissions or NPF. The apparent contributions of charged particles to 3 and 7.5 nm particle formation rates were 5.7 % and 12.7 %, respectively, with mean growth rates of 4.0 nm h-1 between 3-7.5 nm and 5.2 nm h-1 between 7.5 and 22 nm. The ratio of charged to total particle formation rates at 3 nm suggests a minor role for charged particles in NPF. We conclude that NPF is a primary source of &gt; 3 nm ions in our data, with primary emissions being the major source in the absence of NPF.</p

The behaviour of charged particles (ions) during new particle formation events in urban Leipzig, Germany

Air ions are electrically charged particles in air. They are ubiquitous in the natural environment and affect the Earth's radiation budget by accelerating the formation and growth of new aerosol particles. Despite this, few datasets exist exploring these effects in the urban environment. A neutral cluster and air ion spectrometer was deployed in Leipzig, Germany, to measure the number size distribution of charged particles from 0.8 to 42 nm, between 27 July and 25 August 2022. Following previous analyses, charged particles were classified into small (0.8-1.6 nm), intermediate (1.6-7.5 nm), and large (7.5-22 nm) fractions by mass diameter, and their mean concentrations (sum of positive and negative polarities) during the campaign were 405, 71.6, and 415 cm-3, respectively. The largest peaks in intermediate and large ions were explained by new particle formation (NPF), with intermediate ions correlating well with sulfuric acid dimer. Smaller morning and evening peaks were coincident with black carbon concentrations and attributed to primary emissions. NPF events, observed on 30 % of days, coincided with intense solar radiation and elevated sulfuric acid dimer. Small charged particles were primarily associated with radioactive decay and highest during the early hours, and they are unrelated to primary emissions or NPF. The apparent contributions of charged particles to 3 and 7.5 nm particle formation rates were 5.7 % and 12.7 %, respectively, with mean growth rates of 4.0 nm h-1 between 3-7.5 nm and 5.2 nm h-1 between 7.5 and 22 nm. The ratio of charged to total particle formation rates at 3 nm suggests a minor role for charged particles in NPF. We conclude that NPF is a primary source of &gt; 3 nm ions in our data, with primary emissions being the major source in the absence of NPF.</p

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

Non peer reviewe