Insights into Atmospheric Nucleation

Atmospheric aerosol particles have a strong impact on the global climate. A deep understanding of the physical and chemical processes affecting the atmospheric aerosol climate system is crucial in order to describe those processes properly in global climate models. Besides the climatic effects, aerosol particles can deteriorate e.g. visibility and human health. Nucleation is a fundamental step in atmospheric new particle formation. However, details of the atmospheric nucleation mechanisms have remained unresolved. The main reason for that has been the non-existence of instruments capable of measuring neutral newly formed particles in the size range below 3 nm in diameter. This thesis aims to extend the detectable particle size range towards close-to-molecular sizes (~1nm) of freshly nucleated clusters, and by direct measurement obtain the concentrations of sub-3 nm particles in atmospheric environment and in well defined laboratory conditions. In the work presented in this thesis, new methods and instruments for the sub-3 nm particle detection were developed and tested. The selected approach comprises four different condensation based techniques and one electrical detection scheme. All of them are capable to detect particles with diameters well below 3 nm, some even down to ~1 nm. The developed techniques and instruments were deployed in the field measurements as well as in laboratory nucleation experiments. Ambient air studies showed that in a boreal forest environment a persistent population of 1-2 nm particles or clusters exists. The observation was done using 4 different instruments showing a consistent capability for the direct measurement of the atmospheric nucleation. The results from the laboratory experiments showed that sulphuric acid is a key species in the atmospheric nucleation. The mismatch between the earlier laboratory data and ambient observations on the dependency of nucleation rate on sulphuric acid concentration was explained. The reason was shown to be associated in the inefficient growth of the nucleated clusters and in the insufficient detection efficiency of particle counters used in the previous experiments. Even though the exact molecular steps of nucleation still remain an open question, the instrumental techniques developed in this work as well as their application in laboratory and ambient studies opened a new view into atmospheric nucleation and prepared the way for investigating the nucleation processes with more suitable tools.Ilmakehän aerosolihiukkasilla on merkittävä vaikutus globaaliin ilmastoon. Jotta aerosoli ilmasto järjestelmään vaikuttavat prosessit voidaan kuvata oikein ilmastomalleissa, on näiden prosessien tieteellinen tausta ymmärrettävä. Ilmastovaikutusten lisäksi aerosolihiukkasilla on vaikutuksia myös ihmisten terveyteen. Uusia aerosolihiukkasia muodostuu ilmakehän höyryistä. Tämän kaasu - hiukkas muuntuman ensimmäistä vaihetta kutsutaan nukleaatioksi. Ilmakehän nukleaatiomekanismeja ei kuitenkaan yksityiskohtaisesti tunneta. Tärkeimpänä syynä tähän on ollut mittaustekniikoiden puutteellisuus. Vastasyntyneiden neutraalien hiukkasten mittaaminen alle 3 nanometrin kokoluokassa ei ole ollut tähän saakka mahdollista. Tämän työn tarkoituksena on mittaustekniikoita kehittämällä ulottaa havaittavissa oleva hiukkaskokoalue vastanukleoituneiden klustereiden kokoihin, noin 1 nanometriin, saakka, ja suorilla mittauksilla hankkia tietoa alle 3 nanometrin hiukkasten pitoisuuksista ilmakehässä sekä laboratorio-olosuhteissa. Tässä väitöskirjassa esitetyssä työssä mittausongelmaa lähestyttiin neljällä erilaisella kondensaatioon perustuvalla tekniikalla sekä yhdellä sähköiseen havaitsemiseen perustuvalla menetelmällä. Kaikki kehitetyt ja testatut laitteet kykenivät havaitsemaan alle 3 nm hiukkasia, jotkut jopa noin 1 nm saakka. Kehitettyjä tekniikoita ja laitteita käytettiin ilmakehämittauksissa sekä laboratoriokokeissa. Ilmakehämittaukset osoittivat, että pohjoisilla havumetsäalueilla ilmassa on aiemmin tunnetun hiukkaspopulaation lisäksi runsaasti 1-2 nm hiukkasia tai klustereita jotka mahdollisesti voivat toimia tiivistymisytiminä ilmakehän höyryille. Suoritetut laboratoriokokeet osoittivat, että rikkihappo on avainroolissa ilmakehän nukleaatiossa. Kokeilla selitettiin myös aiempien rikkihapolla suoritettujen nukleaatiokokeiden ja ilmakehähavaintojen välinen ristiriita. Syyn osoitettiin liittyvän vastamuodostuneiden hiukkasten riittämättömään kasvuun sekä näiden hiukkasten huonoon havaitsemistehokkuuteen. Vaikka molekyylitasolla nukleaatiota ei vielä pystytty yksityiskohtaisesti selittämään, kehitetyt mittausmenetelmät tuottivat merkittävää uutta tietoa sekä kenttä- että laboratoriomittauksista, avaten uusia näkökulmia ja mahdollisuuksia nukleaatiotutkimukseen

Data protection and privacy in consumer cloud services

Pilvipalveluiden käyttö lisääntyy nopeasti ja yhä useammat sovellukset, jotka ovat perinteisesti olleet työpöytäsovelluksia, ovat siirtyneet pilveen. Sovellusten perässä pilveen siirtyvät myös yritykset sekä oppilaitokset, jotka kasvavissa määrin hylkäävät vanhat perinteiset ohjelmistot ja ottavat pilvipalveluiden hyödyt käyttöönsä. Pilvipalveluiden etuina ovat kustannustehokkuus sekä mahdollisuus käyttää niitä riippumatta paikasta, ajasta tai laitteesta. Tutkimuksen tarkoituksena on selvittää suosituimpien pilvipalveluiden käytön uhkia käyttäjän yksityisyydelle ja tietosuojalle. Aihe on ajankohtainen sillä lähes päivittäin uutisissa on kerrottu pilvipalveluihin liittyvistä tietoturvaongelmista. Tutkimuksessa käy ilmi, että suurimmat ja suosituimmat pilvipalvelut ovat kohtuullisen turvallisia käyttää. Isoilla pilvipalveluita tarjoavilla yrityksillä on varaa panostaa datakeskusten turvallisuuteen, tietoturvien ennaltaehkäisemiseen sekä itse palvelun turvallisuuteen. Yksi suurimmista uhista yksityisyydelle ja tietosuojalle on käyttäjä itse, sillä käyttäjä voi jakaa itsestään liikaa tietoa

Soft X-ray Atmospheric Pressure Photoionization in Liquid Chromatography–Mass Spectrometry

Soft X-ray atmospheric pressure photoionization (soft X-ray APPI) as an ionization method in liquid chromatography-mass spectrometry (LC-MS) is presented. The ionization mechanism was examined with selected test compounds in the negative ion mode, using soft X-ray APPI source emitting 4.9 keV photons. Test compounds with an acidic group were ionized by a proton transfer reaction, producing deprotonated molecules ([M-H](-)), whereas compounds having positive electron affinity were ionized by a charge exchange reaction, producing negative molecular ions (M-.). Soft X-ray APPI does not require a dopant to achieve high ionization efficiency, which is an advantage compared with vacuum ultraviolet APPI with 10 eV photons, in which a dopant is needed to improve ionization efficiency. The energy of the soft X-ray photons is in the keV range, which is high enough to displace a valence electron and often also inner shell electrons from LC eluents and atmospheric gases, initiating an efficient ionization process in the negative ion mode.Peer reviewe

Estimation of sulfuric acid concentration using ambient ion composition and concentration data obtained with atmospheric pressure interface time-of-flight ion mass spectrometer

Sulfuric acid (H2SO4, SA) is the key compound in atmospheric new particle formation. Therefore, it is crucial to observe its concentration with sensitive instrumentation, such as chemical ionisation (CI) inlets coupled to atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometers. However, there are environmental conditions for which and physical reasons why chemical ionisation cannot be used, for example in certain remote places or during flight measurements with limitations regarding chemicals. Here, we propose a theoretical method to estimate the SA concentration based on ambient ion composition and concentration measurements that are achieved by APi-TOF alone. We derive a theoretical expression to estimate the SA concentration and validate it with accurate CI-APi-TOF observations. Our validation shows that the developed estimate works well during daytime in a boreal forest (R-2 = 0.85); however, it underestimates the SA concentration in, e.g. the Antarctic atmosphere during new particle formation events where the dominating pathway for nucleation involves sulfuric acid and a base (R-2 = 0.48).Peer reviewe

On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol : experimental and computational evaluation

Peer reviewe

Effect of addition of four base compounds on sulphuric-acid–water new-particle formation : a laboratory study

Peer reviewe

Chemistry of stabilized Criegee intermediates in the CLOUD chamber

In atmospheric conditions the oxidation of sulphur dioxide to sulphuric acid in gas phase has been considered to be determined by the concentration of hydroxyl radical. Recently the significance of stabilized Criegee intermediate as an oxidizer of sulphuric acid has been brought out. In this study we investigated the oxidation of sulphur dioxide in the CLOUD chamber in conditions where the hydroxyl radical was removed. The concentration of formed sulphuric acid was measured with a chemical ionization atmospheric pressure interface time-of-flight mass spectrometer and it was compared with the calculated yield of sulphuric acid

Applicability of condensation particle counters to measure atmospheric clusters

This study presents an evaluation of a pulse height condensation particle counter (PH-CPC) and an expansion condensation particle counter (E-CPC) in terms of measuring ambient and laboratory-generated molecular and ion clusters. Ambient molecular cluster concentrations were measured with both instruments as they were deployed in conjunction with an ion spectrometer and other aerosol instruments in Hyytiälä, Finland at the SMEAR II station between 1 March and 30 June 2007. The observed cluster concentrations varied and ranged from some thousands to 100 000 cm -3. Both instruments showed similar (within a factor of ~5) concentrations. An average size of the detected clusters was approximately 1.8 nm. As the atmospheric measurement of sub 2-nm particles and molecular clusters is a challenging task, we conclude that most likely we were unable to detect the smallest clusters. Nevertheless, the reported concentrations are the best estimates to date for minimum cluster concentrations in a boreal forest environment

Nucleation of H_2SO_4 and oxidized organics in CLOUD experiment

The research of atmospheric new particle formation has proceeded lately as the role of sulphuric acid has been established. Still, the roles of other atmospheric compounds in nucleation remain largely unclear. To clarify the first steps of atmospheric new particle formation extensive nucleation experiments were performed in CLOUD chamber in 2012. Especially the role of oxidations products of α-pinene was studied in detail. The experiments provided new information about the part of oxidized organics in nucleation