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Browsing by study line "Ilmakehän kemia ja analyysi"

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  • Zhang, Tinghan (2022)
    Air ions can play an important role in new particle formation (NPF) process and consequently influence the atmospheric aerosols, which affect climate and air quality as potential cloud condensation nuclei. However, the air ions and their role in NPF have not been comprehensively investigated yet, especially in polluted area. To explore the air ions in polluted environment, we compared the air ions at SORPES site, a suburban site in polluted eastern China, with those at SMEAR II, a well-studied boreal forest site in Finland, based on the air ion number size distribution (0.8-42 nm) measured with Neutral Cluster and Air Ion Spectrometer (NAIS) during 7 June 2019 to 31 August 2020. Air ions were size classified into three size ranges: cluster (0.8-2 nm), intermediate (2-7 nm), and large (7-20 nm). Median concentration of cluster ions at SORPES (217 cm−3) was about 6 times lower than that at SMEAR II (1268 cm−3) due to the high CS and pre-existing particle loading in polluted area, whereas the median large ion concentration at SORPES (197 cm−3) was about 3 times higher than that of SMEAR II (67 cm−3). Seasonal variations of ion concentration differed with ion sizes and ion polarity at two sites. High concentration of cluster ions was observed in the evening in the spring and autumn at SMEAR II, while the cluster ion concentration remained at a high level all day in the same seasons. The NPF events occurred more frequently at SORPES site (SMEAR II 16% ; SORPES: 39%), and the highest values of NPF frequency at both sites were in spring ((SMEAR II: spring: 43%; SORPES: spring: 56%). During the noon time on NPF event day, the concentration of intermediate ions were 8-14 times higher than same ours on non-event days, indicating that can be used as an indicator for NPF in SMEAR II and SORPES. The median formation rate of 1.5 nm at SMEAR II were higher then that at SORPES, while higher formation rate of 3 nm ions were observed at SORPES. At 3 nm, the formation rate of charged particles was only 11% and 1.6% of the total rate at SMEAR II and SORPES respectively, which supports the current view that neutral ways dominate the new particle process in continental boundary. However, higher ratio between charged and total formation rate of 3 nm particle at SMEAR II indicates ion-induced nucleation can have a bigger contribution to NPF in clear area in comparison to polluted area. Higher median GR of 3-7 nm (SMEAR II: 3.1 nm h−1; SORPES: 3.7 nm h−1) and 7-20 nm (SMEAR II: 5.5 nm h−1; SORPES: 6.9 nm h−1) ions at SORPES were found in comparison to SMEAR II, suggesting the higher availability of condensing vapors at SORPES. This study presented a comprehensive comparison of air ions in completely different environments, and highlighted the need for long-term ion measurements to improve the understanding of air ions and their role in NPF in polluted area like eastern China
  • Pusfitasari, Eka Dian (2019)
    Urine can be used to determine human exposure to nerve agents through the analysis of specific biomarkers. Isopropyl methylphosphonic acid (IMPA) is an important marker of sarin nerve agent, a highly toxic chemical regulated under the Chemical Weapons Convention (CWC). A methodology for sensitive, reliable, and selective determination of IMPA in urine matrix was developed and validated, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample preparation method employs normal phase–solid phase extraction (NP-SPE) using silica based cartridge. Before conducting IMPA analysis, the instrument performance was controlled using a quality control sample. Three different ion sources, namely electrospray ionization (ESI), Unispray, and atmospheric pressure chemical ionization (APCI), were compared in order to define the best method for trace analysis of targeted IMPA. Parameters affecting the ionization process such as cone voltage, capillary voltage, impactor pin voltage, corona voltage, and mobile phase flow rate were optimized. Negative ion mode was selected as the best method for IMPA identification in all three ion sources, and multiple reactions monitoring (MRM) was employed to improve sensitivity and selectivity. The APCI source was shown to be the least sensitive and least efficient ionization technique for IMPA identification. In contrast, using ESI and Unispray resulted in satisfactory data with excellent limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. The two latter ion sources share the same values of those parameters, i.e. 0.44 ng/mL, 1.46 ng/mL, < 4% precision bias, < 5% accuracy bias, for ESI; and 0.42 ng/mL, 1.38 ng/mL, < 4% precision bias, < 4% accuracy bias, for Unispray. Nonetheless, the Unispray shows better performance in comparison to ESI in producing higher signal intensity/peak area and has lower matrix effect.
  • Li, Delun (2024)
    As global concern about climate change grows, particularly in meeting the Paris Agreement’s goal of limiting global warming below 2 °C, studying and observing the effects of light-absorbing aerosol particles in the atmosphere becomes a necessity. This study determined 38 years of equivalent black carbon (eBC) concentrations in Joensuu airport from 1965 to 2003. Samples were originally collected on either cellulose or glass fibre filters for radioactivity monitoring. Measuring black carbon optically from filters comes with its own challenges, such as artefacts caused by scattering aerosol particles and filter material itself. Thus, a calibration setup was built to study the effects of apparent absorption caused by scattering aerosols and the loading effect in various types of filters. First, in the calibration experiments, we examined how different filter materials affect measured transmittance when pure black carbon is deposited, showing non-linear calibration functions. Additionally, we investigated the impact of apparent absorption by depositing various-sized ammonium sulfate particles onto different filter materials, e.g. cellulose and glass fibre. Results showed that apparent absorption depended on the size of the scattering aerosol particles and the filter material. Smaller particles resulted in a 5–38 % overestimation of absorption, while larger particles showed 1–14 %, depending on the transmittance values. In the latter part of the thesis, real sample filters were analyzed with Particle Soot Absorption Photometer for transmittance, and with the conversion functions derived from the first part of the thesis, transmittance values were converted into eBC. For some samples, ion chromatography was used to determine ion concentrations of some scattering particles that alter optical measurements. From 1965 until 1971, cellulose filters were used for collecting aerosol particles, and glass fibre filters were used onwards. Conversion functions obtained from this study were shown to be inadequate for cellulose filters. However, for glass fibre filters, the calculated eBC concentration values were comparable to other studies. Depending on the season, cellulose filters (1965–1971) had 0.25–12 μgm⁻³ of eBC, and glass fibre filters (1972–2003) had eBC of 0.48–3.8 μgm⁻³. For those filters where ions were analyzed, ions contributed up to 30 % overestimation of eBC, making analysis of ions in samples crucial information. Statistically decreasing trends were found in both filters, where in winter had a rate of -22 ngm⁻³yr⁻¹ and -6 ngm⁻³yr⁻¹ in summer. Calculated trends was similar to what was observed in Helsinki. The decrease in eBC can be attributed to the technological advancement in emission control. This comprehensive study enabled the long-term estimation of eBC concentrations solely from transmittance measurements, and provided insights in optical measurements in filters.
  • Franzon, Lauri (2023)
    The oxidation mechanisms of atmospheric organic compounds are an important puzzle piece for many atmospherically relevant topics, including but not limited to air quality and climate change. One poorly understood step in this oxidation process is peroxy radical recombination, in some conditions the most important sink reaction for peroxy radicals, which are formed in abundance due to gas phase reactions in the lower troposphere. After a few initial steps, the peroxy radical recombination reaction results in the ejection of O_2 leaving behind a pair of alkoxy radicals in close proximity. This reactive complex has three known reaction pathways: Hydrogen shift forming an alcohol and a carbonyl compound, radical recombination forming a ROOR dimer, and diffusive break-up forming two free alkoxy radicals. In this thesis, alkoxy bond scission followed by radical recombination resulting in the formation of a ROR is proposed as a fourth reaction pathway. To test the hypothesis, computational chemistry was used to determine alkoxy bond scission rates for radicals of atmospheric significance, and gas-phase oxidation experiments were realized on three peroxy radical precursor molecules to look for signs of ROR formation. More precisely, the Eyring equation was used to calculate the rate of alkoxy bond scission on a potential energy surface determined using density functionals, with corrections to electronic energy using coupled-cluster calculations. In the experiments, liquid phase alkenes were vaporized, and oxidized by O_3 in the gas phase, resulting in peroxy radical formation, after which the possible dimers were detected using a NO_3^- -atmospheric pressure chemical ionization time-of-flight mass spectrometer. A highly oxidized radical reaction partner was present in the chamber to improve the detectability of the formed dimers. The combined results of these two approaches suggest that the reaction pathway is possible in standard atmospheric conditions and may thus be important for a number of peroxy radicals.
  • Kuusisto, Minttu (2023)
    Tässä työssä on karakterisoitu uudentyyppisen ilmaisimen toimintaa haihtuvien orgaanisten yhdisteiden vesimittauksissa. Karakterisointi tehtiin ilmaisimelle, jota on aikaisemmin hyödynnetty vain maaperämittauksissa. Ilmaisimen toimintaa tutkittiin kolmen haihtuvan orgaanisen yhdisteen (asetonin, isopreenin ja metanolin) muodostamien eri väkevyisten vesiliuosten avulla. Ilmaisimen avulla vesiliuoksesta erotetut molekyylit analysoitiin protoninsiirtoreaktio-lentoaikamassaspektrometrilla (PTR-TOF-MS), jonka tuottama data analysoitiin Origin-datankäsittelyohjelmalla. Tutkielmassa perehdytään haihtuviin orgaanisiin yhdisteisiin, ilmaisimen rakenteeseen ja funktionaalisuuteen, diffuusioon, Henryn lakiin ja tulosten tilastolliseen merkitsevyyteen ennen varsinaisia mittaustuloksia. Tuloksissa pohditaan muun muassa virtausnopeuden, lämpötilan ja molekyylikoon vaikutusta vesiliukoisten haihtuvien orgaanisten yhdisteiden mitattuun signaaliin. Lisäksi tuloksissa esitetään arviot tutkitun lampinäytteen asetoni- ja metanolipitoisuuksista kevättalvella. Tämän työn karakterisointitutkimustulosten mukaan ilmaisin toimii kvalitatiivisesti ja loogisesti vesiliukoisten haihtuvien orgaanisten yhdisteiden mittauksissa. Mittauslämpötila vaikuttaa merkittävästi tarkasteltavien yhdisteiden signaalien intensiteetteihin, sillä diffuusio ja haihtuminen ilmaisimessa ovat tehokkaita verrattain korkeassa lämpötilassa. Toisin kuin vesiliukoisten yhdisteiden, rasvaliukoisten yhdisteiden käyttäytymistä ilmaisimessa ei tässä työssä ymmärretty kokonaan.
  • Vinkvist, Netta (2024)
    Aerosol particles are a significant factor both environmentally and in terms of health. They can influence climate change in various ways: certain aerosol particles contribute to warming the atmosphere, while others may have a cooling effect. The concentration of secondary organic aerosol (SOA) in the atmosphere is significant, thus playing a crucial role in the climate. SOA can influence the temperature of the climate and the chemistry of the atmosphere. SOA are formed through the oxidation of volatile organic compounds (VOCs), creating a complex mixture of various less volatile organic compounds with diverse properties. Highly oxygenated organic molecules, products of VOC oxidation, are estimated to explain a substantial part of SOA formation. To assess the climate impacts accurately, it is essential to comprehend the characteristics of SOA in the atmosphere. The aim of the thesis was to investigate the influence of temperature and prefence of dimethyl sulfide (DMS) on the gas-phase oxidation products of VOCs, especially how temperature affects the formation of accretion products. The compounds and ozone reacted in a flow tube, and the resulting oxidation products were ionized by clustering them with reagent ions. The mass-to-charge ratio of the formed charged clusters was then measured with orbitrap mass spectrometer. Identifiable oxidation products were selected based on studies by Rissanen et al. [2014] and Tomaz et al. [2021], and the previously described products in these studies were followed using the Orbitool program. The starting materials used in this thesis were cyclohexene, deuterated cyclohexene, and limonene, which were oxidized in the presence of ozone. Several oxidation products were observed in the measurements that were expected to form based on literature. However, mass spectra also revealed that the reaction time with deuterated cyclohexene might have been too short. With a longer reaction time, the molecules could have undergone further oxidation, allowing better detection of oxidation products. In the thesis, it was observed that temperature influences the formation of oxidized products; as the temperature increases, oxidation reactions progress further in 2.7 s reaction time. Monomers that underwent more extensive oxidation could form more highly oxidized accretion products. DMS likely reacts with hydroxyl radicals, thereby influencing the oxidation of VOC compounds in the flow tube. Measurements conducted with DMS may result in the formation of more organic alkoxy radicals than organic peroxy radicals, which could undergo further oxidation.
  • Vuorio, Niko (2021)
    The Criegee intermediates (CIs) have been the topic for several studies and their role in global atmospheric chemistry is becoming better understood. Isoprene and monoterpenes form a large portion of the total biogenic volatile organic compound emissions in the forested regions of the world, isoprene being the most abundant non-methane hydrocarbon in the Earth's atmosphere. The carbon-carbon double bonds in these compounds are efficiently ozonized (the reaction where an unsaturated compound reacts with ozone) in the atmosphere leading to primary ozonides that subsequently decompose into Criegee intermediates and carbonyl compound molecules. Approximately 50 % of the CIs derived from acyclic alkenes immediately decompose in unimolecular reactions forming, e.g., hydroxyl radicals, the most important oxidizing species in the Earth’s atmosphere. The remainder is stabilized in atmospheric conditions in collisions with other molecules and are subsequently called stabilized Criegee intermediates (sCI). The sCI yields are often smaller, around 20 %, for Criegee intermediates formed in ozonolysis of cyclic alkenes, such as α-pinene. These sCIs can further react with atmospheric constituents (H2O, (H2O)2, SO2, NO2, organic acids etc.) in bimolecular reactions or decompose/isomerize in unimolecular reactions. The bimolecular reactions of sCIs with SO2 contribute significantly to the formation of atmospheric gas phase sulphuric acid and as such are an important factor in nucleation and formation of clouds. In the lower atmosphere, H2SO4 also has adverse health effects on humans and animals and causes corrosion of building materials. Additionally, unimolecular decay and bimolecular reactions of sCIs produce OH radicals. The experimental studies done so far have largely focused on the few simplest sCIs, i.e., formaldehyde oxide (H2COO), acetaldehyde oxide (CH3COO), and acetone oxide ((CH3)2COO). The studies on more complex sCIs, such as methyl vinyl ketone oxide and sCIs formed via ozonolysis of terpenes, are mostly done computationally. The literature review part of this work presents the basic mechanisms of formation and natural removal of sCIs as well as results of recent direct kinetic studies of sCIs with focus on the simplest ones (CH2OO, CH3CHOO, and (CH3)2COO). The methods of detection used in experimental studies are also considered. The experimental section concentrates on measurements of unimolecular decay kinetics of acetone oxide (CH3)2COO above and below room temperature using a new photolytic precursor (CH3)2CIBr. In the experimental section also the apparatus utilized in the research is presented along with the modifications and improvements made on the setup in this work. The calibrations done to ensure accurate measurements are also presented.