Browsing by Subject "Atmosphere-Biosphere Studies"

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  • Shahriyer, Ahmed Hasan (Helsingin yliopisto, 2020)
    The local sources influence the spatial distribution of air pollutants in urban settings, and these can be quite diverse. For better air quality forecasting, constant monitoring of pollutants, and a high volume of measurements are necessary at many locations. Building a dense air quality network by only using the reference instruments is expensive and not feasible. The use of complementary sensor like Vaisala AQT 420 can help achieve the goal of creating a robust air quality network. As part of the Helsinki metropolitan Air Quality Testbed (HAQT) project, AQT 420 was tested for its suitability as a complmentary component in an air quality monitoring network. AQT 420 is capable of measuring NO2, PM2.5, PM10, CO, O3, SO2, relative humidity (RH), temperature, wind speed (WS), wind direction (WD), and air pressure (AP). Proxies for condensation sink (CS), black carbon (BC), particles number concentration (N), and Pegasor AQ urban diffusion current (PAQDCLDSA, which can be parameterized to calculate lung deposited surface area (LDSA) concentrations) were developed for an urban background site in Helsinki, Finland. The intention is to use variables measured by the AQT 420 and predict additional variables by using proxies. Proxy variables will help to maximize the output of AQT 420 sensors, and giving extra data extraction capability from the sensors. PM2.5, NO2, RH and temperature yielded reliable proxies for both CS and PAQDCLDSA with the correlation coefficient r, 0.85 and 0.83, respectively. While, PM2.5, NO2, and NO2, RH were enough to produce satisfactory proxy parameters for BC (r, 0.80), and N (r, 0.76), respectively. Additionally, a campaign data for sulfuric acid (SA) from Helsinki, Finland site was used to produce a proxy for SA. SO2, global radiation, CS and RH gave the best version of that proxy (r, 0.85).
  • Oyekoya, Gboyega Nathaniel (Helsingin yliopisto, 2018)
    Methods for mitigating climate change have been researched for decades. It has been established that most of greenhouse gases (GHG) such as carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) are due to anthropogenic activities. Significant amount of these gases, particularly N2O and CH4 are emitted due to agricultural practices. To boost food supply, nitrogenous fertilizers are the most common fertilizers used in farming, and as the global population will increase to 9 billion by 2050, it is crucial to keep pace with both the population growth and potential economic development. Applying biochar in soil has been regarded as a potential approach to combat climate change while boosting food supplies. In this study, the effect of two different biochars mixed with 15N-labelled ammonium nitrate ( either nitrate NH415NO3, or 15NH4NO3 ammonium labelled) fertilizers in growing Meroa Tetraploid Italian Ryegrasses (Lolium multiflorum) were investigated in Greenhouse Viikki Campus Greenhouse, University of Helsinki, Finland. We monitored the impact of biochars on the aboveground biomasses (g pot-1), roots biomasses (g pot-1), and total biomasses (gram/pot). Furthermore, retention of leachates (nutrient ions) such as atom percentage (at%) 15N-labelled ammonium ion (at% 15NH4-N), mg NH4-N, at% 15N -labelled nitrate ions (at% 15NO3-N %), and mg NO3-N were investigated as well. Lastly, GHG fluxes of N2O-N (ug Kg-1 soil hr-1), CH4-C (ug Kg-1 soil hr-1), CO2-C (mg Kg-1 soil hr-1) were also included in our research for a period of one month in comparison with control samples and fertilized control. Leachates were collected once a week, and gas samplings were measured twice each day for two days in a week. Gases sampled, and leachates collected were analysed, and the plants were detached to obtain the amount of aboveground biomasses (leaves), roots biomasses (roots) and total biomasses (leaves + roots). Our objective affirmed a more eco-friendlly model that biochars can reduce nitrogenous fertilizers applied with an increased agricultural produce. It was concluded that, the effects of different biochars on these mentioned attributes are distinguishable.
  • Tiusanen, Kirsi (Helsingin yliopisto, 2019)
    Continuously progressive climatechange has built a need for sustainable energy source. In the near future we need an alternative source to fossil fuels. At the same time we should secure lower carbon emissions to the atmosphere and increase carbon sinks and accumulate bigger carbon pools to biosphere.Wood based second-generation biofuels are potential option for a sustainable source of energy and therefore an alternative for fossil fuels and also for first-generation biofuels which are produced from food suitable sources. The high cellulose content of wood drives the use as an energy source but long investment time to raw material production impairs the wood’s possibility to be a quick solution to current climate and energy challenges. Hybrid aspen (Populus tremula x tremuloides) as a fast growing tree is one of the species under research to produce cellulose faster. Institute of Biotechnology at University of Helsinki has developed a method for gene manipulation of aspen to enhance the cambial development and tree growth which would shorten the rotation time of harvesting raw material. Simultaneously we need to predict possible side effects that may come with the use of gene manipulation. The wood based production of bioenergy creates a sink for atmospheric carbon dioxide until logging. Furthermore many of the Populus species including aspen emit biogenic volatile organic compounds (BVOC) which slow the climate change due to the secondary particle (SOA) formation. This study investigates seasonal BVOC emission profile and concentration of aspen Populus tremula in natural forest environment during years 2010, 2011 and 2013. The other part of the study concentrates on emissions from gene manipulated hybrid aspen species Populus tremula x tremuloides in greenhouse environment. The results will show the seasonal profile of BVOC emissions and other trace gas exchange (CO2 ,H2O) and their concentration on leaf level. Small part of the atmospheric carbon that tree takes in as CO2 is released back in air as BVOCs and based on these results from three year time aspen releases carbon 0.44-0.57 %per year as BVOVs. The emission profiles show clearly that temperature and light conditions affect to BVOCemission volume. Furthermore, the leaf development phase has a huge effect on seasonal emission profile. The other part of the study that investigate the differences in BVOC emissions between genetic manipulated trees and control trees. Based on these measurements there is no significant difference in BVOC emissions between gene manipulated and wild type hybrid aspen on leaf level. Since environmental conditions affect emission profile and volumes, the climate change with increasing temperature may increase aspen’s seasonal BVOC emissions. Based on measurements of this study the potential use of gene manipulated aspen does not increase BVOC emissionson leaf level but on canopy level the result may be different.
  • Chellapermal, Robert (Helsingin yliopisto, 2018)
    It has proven to be challenging to detect and analyse the tens of thousands of precursors for secondary organic aerosol (SOA) species in ambient air. Models have shown that SOA in particular are still underestimated by an order of magnitude or more. Currently, instrumentation has evolved in the field of atmospheric-pressure mass spectrometers to be able to continuously identify the molecular species in ambient air at high resolution. This includes also neutral clusters if an ionisation mechanism is implemented. Yet, molecular-level information is still missing. The key questions include: What is the bulk density of atmospheric particles? What is the molecular composition of isomeric and isobaric compounds? Most high-resolution mass spectrometers are unable to answer these research questions, as the main output is merely a mass-to-charge (m/z) ratio. By measuring the electrical mobility of these particles, as well as the molecular composition, these questions can be answered. This motivated the atmospheric science community to combine mass spectrometry (MS) instruments with mobility instruments for measuring ambient aerosol and gas phases. An extensively well-defined and studied method, ion mobility spectrometry (IMS), has gained popularity in recent years due to its useful application in the fields of explosives detection and pharmaceutical compound analysis. By coupling an ion mobility spectrometer (IMS) with a time-of-flight mass spectrometer at ambient pressure (APiTOF), we aim at providing additional molecular-level information. With electrospray-ionisation (ESI) and a custom X-ray ion source, neutral clusters can also be detected. For the first time, we have successfully run a 2-month measurement campaign and analysed the data with this setup from a rural boreal forest site in Finland. Before this campaign, calibration of the effective true length of the drift region was performed based on known mobility chemicals (tetra-alkyl-ammonium halides) in the laboratory. The resulting effective length (~19 cm) was utilised to calculate reduced mobility, K0, for all detected masses. Knowing electrical mobility and mass, and assuming spherical particles, density was also computed. All measured compounds in the range of m/z=50 to 500, had lighter bulk density than water calculated. An additional tool linking particles with the same mobility was investigated to show the various applications of the new dataset.Cluster-level analysis of new particle formation (NPF) events and non-events could be further researched and utilised to obtain novel information about molecular clusters.
  • Rajan, Nandita (Helsingin yliopisto, 2019)
    Nitrous oxide (N2O), a major greenhouse gas and long-lived trace gas has been increasing in concentration in the atmosphere since the 1900s. Natural sources including soils account for approximately 62% of the total N2O emitted annually into the atmosphere. Biological processes lead to the production and consumption of nitrous gases in soils. Denitrification, the anaerobic reduction of nitrate to dinitrogen (N2), produces N2O as one of the intermediate volatiles. This process is driven by soil environmental factors such as temperature, moisture and nutrient availability as well as various underlying factors. Anthropogenic activities greatly affect these processes. Boreal peat soils are an important source of nitrous gases due to high content of soil nutrients (carbon and nitrogen) and drained peat soils can become potential ‘hotspots’ for N2O emissions. The environmental factors regulating the emissions are complex and remain unclear. The aim of this study is to investigate the importance of these factors on the emissions of N2O and N2, from drained peatland soil under changing temperature and moisture using measured data and process modelling. Soil samples from drained peatland sites in Southern Finland were collected, the N2 and N2O direct fluxes were measured using the helium-gas-flow soil-core method. To further examine the importance of different factors on the nitrous gas emissions in drained organic soil, a dynamic process-based model, CoupModel was used to simulate similar conditions as those in the laboratory experiment setup for measurement of the fluxes. The model includes a number of parameters which aim to quantify the detailed nitrification-denitrification process. A simple parameterization method was used to define parameter values and estimate the emissions based on the experimental conditions and known soil properties. Parameters were carefully selected and tested for their impact on the N-emissions. Key parameters and factors determining the soil N2O and N2 emissions were thus identified. The results show that nutrient-rich Lettosuo peat produced relatively high N2O (6 x 10-4 g N m-2 day-1) and N2 emission (2.6 x 10-3 g N m-2 day-1) on average as compared to nutrient poor Kalevansuo peat, which showed uptake of N2O (-1.5 x 10-5 g N m-2 day-1) and low N2 emission (0.7 x 10-3 g N m-2 day-1) on average. A significant response to changes in soil environmental conditions, temperature and moisture, was observed in both sites. The model output was consistent with the measurements of abiotic (soil temperature and soil moisture) and biotic responses (soil respiration). The model explained 53% of the variability in measured N2O emissions of the nutrient-rich soil. The dynamics of N2O and N2 emissions were simulated successfully by the model but included overestimation (up to 88%) in the case of N2O. The optimum soil water content for N2O production was between 80-85% vol. Most of the N2O and N2 emissions occurred under anaerobic conditions and hence originated from denitrification. In conclusion, denitrification is the main source of N2O in drained peat soils and soil temperature and water content regulating soil oxygen along with nutrient availability are the major factors influencing this process. Management practices as well as climate change can potentially influence these factors thus leading to changes in the greenhouse gas emissions origination from soils.
  • Ghasemi Falk, Homa (Helsingin yliopisto, 2019)
    Greenhouse gases are essential in controlling the surface temperature of the Earth. Methane is one of the most abundant greenhouse gases in the atmosphere. it has an important role in the atmospheric chemical processes, and its atmospheric concentration has increased dramatically from pre-industrial time. In 2006, studies revealed that terrestrial plants are capable of emitting methane under aerobic conditions which led to the conclusion that the contribution of forests to the global methane budget needs to be considered. In my thesis the aim was to assess the capacity of boreal tree stems to transport methane, to quantify the radial diffusivity of methane in the stem of different tree species and evaluate the effects of various factors on regulating stem gas transport. Gas transport of Scots pines (Pinus sylvestris) and Birches (Betula pubescens) tree stems were examined in the laboratory under controlled conditions. The results highlighted that birch stem samples have a higher methane stem fluxes compared to pine samples. The result also indicated that birches accumulated less methane inside the stem compare with pine samples. One of the most significant findings from this study is that birch stem samples have the higher average methane and carbon dioxide diffusivity compared to pine samples. This finding also explains the smaller accumulated methane gas inside the birch stems compared to pine stems. Also, the differences in the diffusivity may result from differences in the anatomical composition of these tree species, including heartwood, sapwood, bark tissue and lenticel densities.