Browsing by Subject "new particle formation"
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(2020)This thesis presents the Atmospherically Relevant Chemistry and Aerosol Box Model (ARCA box), which is used for simulating atmospheric chemistry and the time evolution of aerosol particles and the formation of stable molecular clusters. The model can be used for example in solving of the concentrations of atmospheric trace gases formed from some predefined precursors, simulation and design of smog chamber experiments or indoor air quality estimation. The backbone of ARCAs chemical library comes from Master Chemical Mechanism (MCM), extended with Peroxy Radical Autoxidation Mechanism (PRAM), and is further extendable with any new reactions. Molecular clustering is simulated with the Atmospheric Cluster Dynamics Code (ACDC). The particle size distribution is represented with two alternative methods whose size and grid density are fully configurable. The evolution of the particle size distribution due to the condensation of low volatile organic vapours and the Brownian coagulation is simulated using established kinetic and thermodynamic theories. The user interface of ARCA differs considerably from the previous comparable models. The model has a graphical user interface which improves its usability and repeatability of the simulations. The user interface increases the potential of ARCA being used also outside the modelling community, for example in the experimental atmospheric sciences or by authorities.
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(2023)The Arctic is warming approximately four times as fast as the rest of the planet, and the current and future changes may have drastic effects on the entire globe. However, the detailed processes of the Arctic climate have been studied to a small extent due to the remote and hard-to-reach location, and the representation of the Arctic in climate models has been inadequate. There are many uncertainties in climate models, and significant uncertainties concern aerosol-related information. Atmospheric aerosols have a large, yet not entirely understood and quantified effect on the climate. Aerosols affect the Earth’s radiative balance by scattering and absorbing incoming radiation, and they play a significant role in the cloud formation process. In order to improve the representation of the Arctic in climate models and tackle the unsolved questions about the Arctic atmosphere, sea ice, ocean, biogeochemistry and ecosystem, a one-year-long expedition called Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted in the central Arctic between September 2019 and October 2020. As secondary aerosol formation (new particle formation) produces more than 50% of the atmospheric cloud condensation nuclei, and iodic acid has been identified to be a significant compound for new particle formation in the Arctic pristine environments, the iodic acid concentrations during the full-year MOSAiC expedition was investigated. The main research objective was to quantify the seasonal cycle of iodic acid in the Arctic. The correlation with temperature, solar radiation and ozone were also studied. Together with ice dynamics, sea ice thickness and air mass back trajectory simulations, the possible sources of measured iodic acid were investigated. The participation in forming new particles was also studied. The measured iodic acid concentrations varied between 1e4 and 4e7 molecules/cm3 with a detection limit of 1.22e5 molecules/cm3, and the concentrations were in the same range with measured earlier in the Arctic. The highest concentrations were measured in April. An increased correlation of iodic acid concentration with temperature and radiation was observed during spring, and an anticorrelating trend was observed between iodic acid concentration and ozone during the period of high iodic acid, implying that iodic acid is partially responsible for ozone depletion in the arctic. Comparison with particle data showed that iodic acid concentrations measured during MOSAiC were sufficient to take part in the new particle formation. However, nucleation was not observed during the highest iodic acid concentration period in April.
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(2022)The effects of atmospheric aerosol particles on Earth’s radiative balance are mainly cooling, which is mostly due their indirect effects with clouds. In the Arctic more than half of the cloud condensation nuclei (CCN) production is originated from secondary aerosols, and to further the understanding of Arctic climate and its changes due to the global warming, it is necessary to better understand the secondary aerosol processes there. Highly oxygenated organic molecules (HOM) are known to be important for the formation and especially for the growth of newly formed secondary aerosols to climate relevant sizes. Because of the low volatilities of HOM, they can condense onto the smallest particles, which is crucial for the growth of the new particles. Volatile organic compounds (VOC), especially monoterpenes, are known to be sources of HOM in boreal forest, but in the Arctic where the vegetation is scarce the sources of HOM have not yet been identified. The processes related to secondary aerosol formation in the Arctic are still not fully understood. Especially the observations of HOM and their sources are lacking. Recent studies in Ny-Ålesund, Svalbard showed that multiple aerosol precursors are found to be present in the Arctic atmosphere, as well as contributing to the early stages of the formation of secondary particles. However, more molecular scale observations of aerosol precursors are still needed to form a full picture of the Arctic climate processes. In this thesis, the different aerosol precursors and their contributions to the new particle formations in high Arctic location Ny-Ålesund, Svalbard were analysed. Chemical compositions of HOM were identified for the first time from Arctic atmosphere, and their contributions to new particle formation in high Arctic location were investigated. Because of the high concentrations of HOM during the observed NPF events, it can be suggested that they were contributing to the nucleation of aerosol particles. Particle growth rate calculation shows that the HOM present in the study site were responsible for up to 50% of the total growth of the newly formed particles. VOC flux measurements done in same location were also analysed, and Arctic tundra in Svalbard was found out to be a source of at least four different VOC. Furthermore, the identified HOM were linked to the VOC flux measurements, suggesting a possible link between Arctic VOC and HOM.
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