Browsing by master's degree program "Magisterprogrammet i atmosfärsvetenskaper"

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.

Topic of this Master's thesis was to study how different forest management practises can influence the climate change mitigation potential of Finnish pine forests. Study was carried out with a land ecosystem model JSBACH-FOM. Topic was analyzed by comparing the changes in the carbon budget, surface albedo and the water balance over a 45 year period under different management scenarios. Harvest scenarios used were ecology oriented, balanced and profit oriented harvest. In the ecology oriented harvest scenario mainly old pines are harvested, while in the profit oriented scenario harvests are directed towards younger pines preventing them from reaching old ages. Balanced harvest scenario is between the two. Model was also run under two future climate scenarios, RCP 4.5 and RCP 8.5 in order to determine if the scale of climate change affects results of different harvest scenarios. Profit oriented harvesting results in both the largest positive and largest negative impacts in comparison to if forest was left unmanaged. Ecologically oriented is the opposite, and balanced is in between. No significant differences were found between the climate scenarios in any of the modelled variables.

In order to reliably quantify the impact of cities to the climate change, carbon dioxide (CO2) fluxes from urban areas need to be accurately estimated. Currently, eddy covariance (EC) measurements of net ecosystem exchange (NEE) are among the most used methods for CO2 balance assessment at ecosystem scale. They cannot, however, directly separate gross primary production (GPP) from different sources of CO2 , but instead different tracers and methods need to be used for the separation. In this thesis, urban carbonyl sulfide (COS) fluxes are reported and used as a tracer for biogenic CO2 uptake. For estimating GPP, a leaf-relative uptake (LRU) of CO2 and COS during photo- synthesis has to be calculated. Three different methods for ecosystem scale LRU estimations are compared in order to find which performs the best at assessing urban GPP from EC measurements. LRUNEE method is based on averaging LRU obtained directly from an equation using EC measurements of CO2 and COS. LRUP AR uses parameterisation of photosynthetically available radiation (PAR) to estimate LRU, and LRUCAP uses additional environmental parameters and information of soil water content (SWC), water vapour pressure deficit (VPD) and PAR. EC measurements were conducted at SMEAR III station (ICOS ecosystem associate site) in Helsinki during summer 2022 using a quantum cascade laser gas analyser. Mole fractions of COS, CO2, CO, and water vapour were collected with 10 Hz frequency, together with three-dimensional wind speed measurements. 30-min fluxes were calculated and used for estimating LRU and GPP with the three methods above. Source area of the station was divided into urban, street, and vegetation sectors. To compare different LRU methods, EC measured GPP from vegetation sector was used because it had the smallest anthropogenic emissions. CO and COS fluxes were compared to estimate co-emissions from fuel combustion. Median COS flux of −25.5 pmol m−2 s−1 was measured, indicating a biogenic CO2 uptake in the study area. For simplicity, soil related COS fluxes were neglected. LRUPAR performed the best at estimating GPP, giving an average CO2 uptake of 13.9 μmol m−2 s−1 for the vegetation sector. Furthermore, peak median anthropogenic emissions of 9.1 μmol m−2 s−1 were deduced with LRUPAR, which agrees with earlier research. However, due to problems with instrumentation the data collection period was so short that distinction between LRUPAR and LRUCAP was not unambiguous. Clear is that setting a constant value for LRU leads to significant underestimation of GPP, and a misunderstanding of its behaviour in heterogeneous urban landscape. Further development of COS based GPP estimation should include a more careful instrumentation and revision of the parameterisation of LRUCAP method.

In atmospheric sciences, measurements provided by remote-sensing instruments are crucial in observing the state of atmosphere. The associated uncertainties are important in nearly all data analyses. Random uncertainties reported by satellite instruments are typically estimated by inversion algorithms (ex-ante). They can be incomplete due to simplified or incomplete modelling of atmospheric processes used in the retrievals, and thus validating random uncertainties is important. However, such validation of uncertainties (or their estimates from statistical analysis afterwards, i.e. ex-post) is not a trivial task, because atmospheric measurements are obtained from the ever-changing atmosphere. This Thesis aims to explore the structure function method – an important approach in spatial statistics – and apply it to total ozone column measurements provided by the nadir-viewing satellite instrument TROPOMI. This method allows us to simultaneously perform validation of reported ex-ante random uncertainties and to explore of local-scale natural variability of atmospheric parameters. Two-dimensional structure functions of total ozone column have been evaluated based on spatial separations in latitudinal and longitudinal directions over selected months and latitude bands. Our results have indicated that the ex-post random uncertainties estimated agree considerably well with the reported ex-ante random uncertainties, which are within 1-2 DU. Discrepancies between them are very small in general. The morphology of ozone natural variability has also been illustrated: ozone variability is minimal in the tropics throughout the year, whereas in middle latitudes and polar regions they attain maxima in local spring and winter. In every scenario, the ozone structure functions are anisotropic with a stronger variability in the latitudinal direction, except at specific seasons in polar regions where isotropic behaviour is observed. Our analysis has demonstrated that the structure function method is a remarkable and promising tool for validating random uncertainties and exploring natural variability. It has a high potential for applications in other remote sensing measurements and atmospheric model data.

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.

Tässä tutkielmassa tarkastellaan horisontaalisten gravitaatiovaihteluiden vaikutusta ilmakehän perusyhtälöihin sekä yksinkertaisen ilmakehämallin tuloksiin erilaisissa simulaatioissa. Työn motivointina oli tutkia putoamiskiihtyvyyden vaikutusta mallinnustarkkuuteen, koska se on yksi monista säänennustus- ja ilmastosimulaatioihin liittyvistä epätarkkuustekijöistä. Ilmakehän perusyhtälöt johdettiin aluksi uudelleen huomioimalla gravitaation vaihtelu vaakasuunnassa. Tämän jälkeen vastaavat yhtälömuutokset tehtiin SPEEDY-mallin lähdekoodiin, ja mallin avulla tehtiin simulaatioita gravitaatiovaihteluiden vaikutusten selvittämiseksi. Jotta tulosten analysointi olisi mahdollisimman helppoa, käytettiin simulaatioissa paljon yksinkertaistuksia. Näistä merkittävin oli mallimaapallon korvaaminen vesiplaneetalla. Yhtälömuutosten oikeellisuus mallissa verifioitiin yhden aika-askeleen kokeilla, minkä jälkeen muokatuille perusyhtälöille tehtiin suuruusluokka-analyysi. Analyysin perusteella gravitaatiovaihteluista aiheutuvat lisätermit olivat pääosin yhdestä kahteen kertaluokkaa yhtälöiden muita termejä pienempiä. Lopuksi tehtiin kymmenen vuoden simulaatioita, joissa tarkasteltiin niin sanotun normaaligravitaatiojakauman vaikutuksia mallin tuloksiin. Näissä kokeissa havaittiin, että meteorologisten suureiden anomaliat olivat pääosin maltillisia, mutta eivät merkityksettömän pieniä. Esimerkiksi tuulikentässä havaitut muutokset olivat suurimmillaan noin 2 m/s, kun taas lämpötila-anomaliat jäivät globaalisti alle puoleen asteeseen. Meridionaalisen kiertoliikkeen anomaliassa havaittiin puolestaan selkeä antisymmetria pallonpuoliskojen välillä: intertrooppinen konvergenssivyöhyke siirtyi päiväntasaajalta leveyspiirin 10°S tienoille, kun taas leveyspiirillä 5°N nousuliike heikkeni. Lisäksi länsituulet hidastuivat pohjoisen pallonpuoliskon keskileveysasteilla, mutta voimistuivat eteläisellä pallonpuoliskolla. Tulosten perusteella aiheen tutkimista kannattaa jatkaa myös tulevaisuudessa.

The legislation of the Paris Agreement obliges Finland to pursue actions that keep the global average temperature rise below 2°C and aim to limit the average temperature rise to 1.5°C. The current Finnish government has aligned the national goal of carbon neutrality by 2035. The role of municipalities in promoting or compensating carbon sinks has not yet been defined, although municipalities play an important role as a platform for climate work at local and regional levels. However, it is already known that the Finnish National Climate Act, which is being reformed at this moment, will be subject to an obligation to produce their own climate programs at municipal, regional or provincial level. Environmental competence and environmental development have been important in Lahti for several decades already. The City of Lahti has set its target for carbon neutrality for 2025 and it includes targets for reducing, compensating, and increasing carbon sinks. This work focused on the examination of carbon sequestration and sinks in an urban environment in Lahti, in the example area of approximately 82 hectares, through which a wider understanding of the city's potential to grow coal stocks and sinks in a tight urban structure within different land use classes and different ground cover between them. Based on the Finnish Environment Agency's CORINE land cover classification, the current potential of carbon sequestration for urban land use classes were calculated in this work and the actions to increase carbon sequestration capacity were identified. The work examined the availability of the finished spatial data and to supplement incomplete information, existing literature on the topic was used, as well as other existing spatial records of the city of Lahti and previously made surveys. The largest carbon sink was observed in forest areas, of which in mixed forests representing the largest forest type in the area. Through the calculations and literature carbon sinks and stocks in residential areas were also found to be significant in terms of vegetation, as well as in terms of soil based on the literature review. In planting street and park trees for the purpose of increasing the carbon sink, the most important thing was found to be the long lifetime of trees and securing it. Growing of carbon sinks is most effective in areas where carbon sequestration is already at a high level but increasing vegetation cover in all urban land covers will increase the carbon sink in the long run. One major conclusion of the work was that Lahti's current method of determining carbon sinks and stocks has been inadequate at least for the determining them in built areas, and future measures to maintain, preserve and increase carbon stocks and sinks would not be seen by the same calculation method in the computing. In general, the research data and methods are still largely based on observations and results from the operational processes of natural ecosystems, and these are utilized in urban planning, construction, and maintenance of urban green areas. An incomplete knowledge of the ecological processes in urban areas is a problem that produced challenges in this work as well. More research data is needed on carbon sinks in urban land use classes to gain a more secure understanding of carbon sinks and stocks, although the common importance of vegetation in urban areas is already clear. Although the work focused on carbon in an urban environment, it is necessary to remember the diversity of the urban environment and the other ecosystem services it produces. Land use planning, as well as the management of green spaces in the urban environment, can enhance both the size of carbon storages and sinks and biodiversity and they do not have to be entirely separate from each other.

Low-level wind shear is a significant aviation hazard. A sudden reduction in the headwind along an aircraft flight path can induce a loss of lift, from which an aircraft may not be able to recover when it is close to the ground. Airports therefore use low-level wind shear alert systems to monitor wind velocities within the airport terminal area and alert of any detected hazardous wind shear. There exist three ground-based sensor systems capable of independently observing low-level wind shear: a Doppler weather radar-based, a Doppler wind lidar-based, and an anemometer-based system. However, as no single sensor system is capable of all-weather wind shear observations, multiple alert systems are used simultaneously, and observations from each system are integrated to produce one set of integrated wind shear alerts. Algorithms for integrating Doppler weather radar and anemometer wind shear observations were originally developed in the early 1990s. However, the addition of the Doppler wind lidar-based alert system in more recent years warrants updates to the existing radar/anemometer integration algorithms. This thesis presents four different replacement candidates for the original radar/anemometer integration algorithms. A grid-based integration approach, where observations from different sensor systems are mapped onto a common grid and integrated, is found to best accommodate central integration considerations, and is recommended as the replacement to the original radar/anemometer algorithms in operational use. The grid-based approach is discussed in further detail, and a first possible implementation of the algorithm is presented. In addition, ways of validating the algorithm and adopting it for operational use are outlined.

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.

Ilmatieteen laitoksen ylläpitämä Suomen virallisten sademittarien havaintoverkko on harva ja sen laajentaminen vaatisi enemmän resursseja. Kansalaisten sadehavaintojen hyödyntäminen olisi yksi keino laajentaa havaintoverkkoa ja siten muun muassa parantaa sääennusteiden laatua. Tässä tutkielmassa selvitettiin kansalaisten Netatmo-kesäsadehavaintojen käyttökelpoisuutta Suomessa. Vuosien 2019–2022 kesä-, heinä- ja elokuun Netatmo-sadehavaintojen laatua tutkittiin vertailemalla niitä Ilmatieteen laitoksen automaattisadeasemien havaintoihin. Vertailua tehtiin tilastollisten suureiden, keskiarvon, korrelaation ja absoluuttisen keskivirheen, avulla. Ennen varsinaista analyysia pyrittiin rajauksilla selkeyttämään aineistoa sekä poistamaan siitä selvästi virheellisiä Netatmo-sadeasemia ja -havaintoja, kuten yli 150 mm:n tunti- ja yli 200 mm:n vuorokausisademäärät. Pääsääntöisesti Netatmo-sadehavainnot näyttävät tilastollisten suureiden valossa hyviltä, sillä esimerkiksi 75 % Netatmo- ja lähimpien Ilmatieteen laitoksen asemien välisistä vuorokausisateiden korrelaatioista oli vähintään 0.6. Netatmo-havaintojen välinen vaihtelu oli kuitenkin suurempi kuin Ilmatieteen laitoksen asemien havaintojen, mikä kertoo osan Netatmo-havainnoista olevan virheellisiä. Virheitä löytyi useita erilaisia. Yleisesti monien Netatmo-asemien havaittiin aliarvioivan sademäärää, koska keskimäärin Netatmo-asemat olivat mitanneet sateita vajaat 10 % vähemmän kuin niiden vertailuasemat. Lisäksi Netatmo-asemien havainnoissa oli huomattavasti enemmän pieniä 0.1 mm mittauksia kuin Ilmatieteen laitoksen vertailuasemilla eikä osa asemista ollut mitannut mitään 0.1 mm virhemittauksia lukuunottamatta. Jotkut Netatmo-asemat puolestaan mittasivat yksittäin tai jopa jatkuvasti virheellisiä hyvin suuria sademääriä. Osa asemista myös yliarvioi sademäärää, sillä asemien sateet korreloivat hyvin vertailuasemien sateiden kanssa ollen vain paljon suurempia. Toisaalta joidenkin Netatmo-asemien realistiset sadehavainnot oli mitattu eri aikoihin kuin vertailuasemien sateet, joten asemien koordinaatit voivat olla väärät. Välillä taas Netatmo-havaintojen laatu muuttui ajan myötä, sillä kyse on kansalaisten havainnoista. Asemat saattoivat ensin tuottaa hyviä havaintoja ja sitten huonoja tai päinvastoin. Kaikkiaan Netatmo-kesäsadehavainnot vaikuttavat käyttökelpoisilta, koska suurin osa havainnoista on hyviä. Netatmo-asemat myös saavat suuria sateita kiinni hyvin. Lisäksi huonoja havaintoja korrelaation perusteella tuottavat Netatmo-asemat ovat hajallaan eri puolilla Suomea ja hyviä asemia on kaikkialla enemmän. Koska virheellisiä Netatmo-asemia ja -havaintoja on silti varsin paljon, Netatmo-sadehavainnot tarvitsevat kattavaa laadun varmistusta ennen havaintojen hyödyntämistä. Laadun varmistusta voisi tehdä tämän tutkimuksen tavoin vertailemalla havaintoja tilastollisesti Ilmatieteen laitoksen asemien havaintoihin. Lisäksi Netatmo-havaintoja voisi verrata keskenään.