Kohti yhdenmukaisempia pyörrekovarianssitekniikalla mitattuja metaanivoita

Methane (CH4) is a strong greenhouse gas and its surface mixing ratio has increased by 150 % since the pre-industrial era. The aggregated atmospheric CH4 budget is relatively well-constrained, however the contribution of different sources/sinks to the overall budget is not. The exchange of matter and energy between the atmosphere and different ecosystems can be studied with eddy covariance (EC) technique. Recently, instrumentation suitable for EC measurements of CH4 fluxes have become available, however, measurement and data processing methodologies are yet to be standardised. By including instrument and software intercomparisons, this thesis is aimed to advance the harmonisation of EC CH4 flux measurement and data processing methodologies. Data from two sites are utilized: Siikaneva fen in Southern Finland and Cabauw agricultural peatland in the Netherlands. Improvement in CH4 instrumentation was exemplified in this work by the decrease in the signal noise: the new CH4 gas analysers showed approximately 10-times lower noise levels than the older models. Cumulative CH4 emissions agreed within 7 % which suggests that there was no significant bias between the instruments. Another possible source of uncertainty is EC data processing. Two widely used EC data processing programs computed comparable CH4 fluxes for different instrument and data processing combinations and thus the data processing routines were implemented similarly. The significance of careful EC data processing was demonstrated by the fact that occasionally the flux corrections contributed over 100 % of the measured signal. EC CH4 fluxes showed high spatial variability in an agricultural peatland ecosystem, considerably higher than the other fluxes. The variability hinders the scalability of EC CH4 fluxes to larger spatial scales and scaling is needed if the CH4 balance of the whole landscape is evaluated. Therefore, the usability of tall flux tower to measure the landscape fluxes directly was also explored. While the results from this exercise were encouraging, the morning and evening transition periods proved to be difficult for the tall flux tower system. This thesis sets a benchmark for the precision and accuracy of EC CH4 data by evaluating instrumentation and data processing tools. Further, the thesis raises awareness of possible problems when upscaling short tower EC CH4 measurements due to flux variability within the landscape. Finally, the findings can be used by researches in the future to evaluate the reliability of their EC CH4 data and thus the thesis contributes to the harmonisation of EC CH4 methodologies.Metaani (CH4) on voimakas kasvihuonekaasu ja sen alailmakehän pitoisuus on kasvanut 150 % esiteollisiin aikoihin verrattuna. Kaikkien ilmakehän CH4:n lähteiden ja nielujen nettovaikutus voidaan määrittää melko tarkasti, mutta erillisten lähteiden/nielujen vaikutuksen määrittäminen on huomattavasti vaikeampaa. Ilmakehän ja erilaisten ekosysteemien välillä tapahtuvaa aineen ja energian vaihtoa voidaan mitata pyörrekovarianssimenetelmällä (suora vuomittaus, eddy covariance , EC-menetelmä). EC-mittauksiin soveltuvien CH4 analysaattorien määrä markkinoilla on kasvanut viime aikoina voimakkaasti ja tämä on johtanut tällaisten vuomittausten nopeaan yleistymiseen. Siksi mittaustapojen ja -tulosten prosessointimenetelmien yhdenmukaistamista tarvitaan pikaisesti. Tämä väitöskirjatyö vastaa osaltaan tähän tarpeeseen. Tässä työssä vertaillaan muun muassa eri CH4 laitteita ja datan prosessointimenetelmiä/ohjelmistoja ja käytetään mittauksia kahdelta asemalta: Siikaneva-suolta Etelä-Suomessa ja maatalouskäytössä olevalta turvemaalta Cabauw:ssa, Alankomaissa. Vuosien saatossa tapahtunutta CH4 mittalaitteiden kehittymistä havainnollistettiin tässä työssä vertailemalla eri laitteiden signaalin kohinaa. Uusien analysaattorien kohinan taso oli noin 10-kertaa pienempi kuin vanhemmilla malleilla. Eri laitteiden avulla määritetyt kumulatiiviset CH4-päästöt vaihtelivat 7 % sisällä, mikä viittaa siihen, että laitteiden välillä ei ollut merkittävää systemaattista eroa. Toinen mahdollinen epävarmuustekijä CH4 vuomittauksissa on prosessoinnista johtuvat virheet. Tässä työssä vertailtiin kahta laajasti käytössä olevaa prosessointiohjelmaa ja ne tuottivat samanlaisia lopputuloksia erilaisille prosessointimenetelmä ja mittalaite yhdistelmille. Tässä työssä osoitettiin myös, että EC-datan prosessointi vaatii tarkkuutta: hetkittäin joihinkin mittauksiin tehtävät korjaukset olivat yli 100 % alun perin mitatusta signaalista. EC-menetelmällä Cabauw:n turvemaalla mitatut CH4 vuot vaihtelivat spatiaalisesti merkittävästi enemmän kuin muut mitatut vuot. Tämä vaihtelu vaikeuttaa vuomittausten skaalausta isommalle alueelle ( upscaling ), mikä on välttämätöntä jos mittausten perusteella tahdotaan arvioida laajemman alueen CH4 vaihtoa. Sen vuoksi tässä työssä tutkittiin myös, että voitaisiinko korkeaan torniin asennetulla EC-mittaussysteemillä mitata koko ympäröivän maiseman CH4 vaihtoa suoraan. Vaikkakin tämän harjoituksen tulokset olivat lupaavia, niin auringonnousun ja -laskun aikaan korkean tornin mittaukset osoittautuivat epäedustaviksi. Tässä väitöskirjatyössä määritettiin EC-tekniikalla mitattujen CH4 voiden systemaattiset ja satunnaiset virheet muun muassa vertailemalla mittalaitteita ja ohjelmistoja. Lisäksi työ painottaa, että CH4 voiden spatiaalista vaihtelua ei pidä unohtaa, jos EC-tekniikalla mitattuja CH4 voita skaalataan isommalle alueelle. Tämän työ tuloksia voidaan käyttää tulevaisuudessa CH4 vuomittausten oikeellisuuden arvioinnissa ja täten tämä työ edistää EC-menetelmien yhdenmukaistamista

Field intercomparison of four methane gas analysers suitable for eddy covariance flux measurements

Eddy covariance (EC)-flux measurement technique is based on measurement of turbulent motions of air with accurate and fast measurement devices. For instance, in order to measure methane flux a fast methane gas analyser is needed which measures methane concentration at least ten times in a second in addition to a sonic anemometer, which measures the three wind components with the same sampling interval. Previously measurement of methane flux was almost impossible to carry out with EC-technique due to lack of fast enough gas analysers. However during the last decade new instruments have been developed and thus methane EC-flux measurements have become more common. Performance of four methane gas analysers suitable for eddy covariance measurements are assessed in this thesis. The assessment and comparison was performed by analysing EC-data obtained during summer 2010 (1.4.-26.10.) at Siikaneva fen. The four participating methane gas analysers are TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) and Prototype-7700 (LI-COR Biosciences, USA). RMT-200 functioned most reliably throughout the measurement campaign and the corresponding methane flux data had the smallest random error. In addition, methane fluxes calculated from data obtained from G1301-f and RMT-200 agree remarkably well throughout the measurement campaign. The calculated cospectra and power spectra agree well with corresponding temperature spectra. Prototype-7700 functioned only slightly over one month in the beginning of the measurement campaign and thus its accuracy and long-term performance is difficult to assess.Eddy covariance (EC)-vuonmittausmenetelmä perustuu ilman turbulenttisten liikkeiden mittaamiseen tarkoilla ja nopeilla mittalaitteilla. Esimerkiksi metaanivuon mittaamiseen tarvitaan nopea kaasuanalysaattori, joka mittaa metaanin konsentraatiota vähintään kymmenen kertaa sekunnissa, sekä anemometri, joka mittaa tuulen kolmea komponenttia samalla mittaustaajuudella. Aiemmin metaanin EC-vuomittauksia oli lähes mahdotonta toteuttaa, koska tarpeeksi nopeita ja helppokäyttöisiä kaasuanalysaattoreita ei ollut markkinoilla. Kuitenkin viimeisen vuosikymmenen aikana uusia mittalaitteita on kehitetty ja näin ollen metaanin EC-vuomittaukset ovat yleistyneet. Tässä opinnaytteessä vertaillaan ja arvioidaan neljän metaanikaasuanalysaattorin toimintaa sekä näiden avulla määritettyjä metaanivoita. Tämä toteutettiin analysoimalla Siikanevalla, vuoden 2010 kesällä (1.4.-26.10.) tehtyjä EC-metaanivuomittauksia. Mittauskampanjaan osallistuneet neljä kaasuanalysaattoria ovat: TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) ja Prototype-7700 (LI-COR Biosciences, USA). RMT-200 toimi luotettavimmin läpi mittauskampanjan ja sen avulla määritetyllä metaanivuolla oli keskimäärin pienin satunnainen virhe. Lisäksi kaasuanalysaattoreiden G1301-f ja RMT-200 mittauksista lasketut metaanivuot täsmäävät erittäin hyvin. Kaikkien mittalaitteiden mittauksista lasketut turbulenttiset kospektrit ja tehospektrit täsmäävät kohtuullisen hyvin lämpötilan vastaavien spektrien kanssa. Prototype-7700 toimi vain reilun kuukauden verran mittauskampanjan alussa, joten sen mittaustarkkuutta ja pitkän ajan toimintakykyä on vaikea arvioida

Quantifying the coastal urban surface layer structure using distributed temperature sensing in Helsinki, Finland

The structure of the urban boundary layer, and particularly the surface layer, displays significant complexity, which can be exacerbated by coastal effects for cities located in such regions. Resolving the complexity of the coastal urban boundary layer remains an important question for many applications such as air quality and numerical weather prediction. One of the most promising new techniques for measuring the structure of the surface layer is fibre-optic distributed temperature sensing (DTS), which has the potential to provide new significant insights for boundary layer meteorology by making it possible to study thermal turbulence with high spatial and temporal resolution. We present 14 weeks of profile measurements with a DTS system at an urban site in Helsinki, Finland, during the winter and spring of 2020. We assess the benefits and drawbacks of using DTS measurements to supplement sonic anemometry for longer measurement periods in varying meteorological conditions, including those found difficult for the DTS method in prior studies. Furthermore, we demonstrate the capabilities of the DTS system using two case scenarios: a study of the erosion of a near-ground cold layer during the passage of a warm front, and a comparison of the near-ground thermal structure with and without the presence of a sea-breeze cell during springtime convective boundary layer development. This study demonstrates the utility of DTS measurements in revealing the internal surface layer structure, beyond the predictions of traditional surface layer theories. This knowledge is important for improving surface layer theories and parametrisations, including those used in numerical weather prediction. The study also highlights the drawbacks of DTS measurements, caused by low signal-to-noise ratios in near-neutral atmospheric conditions, especially when such a system would be used to supplement turbulence measurements over longer periods. Overall, this study presents important considerations for planning new studies or ongoing measurements utilising this exciting and relatively new instrumentation.Peer reviewe

Random uncertainties of flux measurements by the eddy covariance technique

Large variability is inherent to turbulent flux observations. We review different methods used to estimate the flux random errors. Flux errors are calculated using measured turbulent and simulated artificial records. We recommend two flux errors with clear physical meaning: the flux error of the covariance, defining the error of the measured flux as 1 standard deviation of the random uncertainty of turbulent flux observed over an averaging period of typically 30 min to 1 h duration; and the error of the flux due to the instrumental noise. We suggest that the numerical approximation by Finkelstein and Sims (2001) is a robust and accurate method for calculation of the first error estimate. The method appeared insensitive to the integration period and the value 200 s sufficient to obtain the estimate without significant bias for variety of sites and wide range of observation conditions. The filtering method proposed by Salesky et al. (2012) is an alternative to the method by Finkelstein and Sims (2001) producing consistent, but somewhat lower, estimates. The method proposed by Wienhold et al. (1995) provides a good approximation to the total flux random uncertainty provided that independent cross-covariance values far from the maximum are used in estimation as suggested in this study. For the error due to instrumental noise the method by Lenschow et al. (2000) is useful in evaluation of the respective uncertainty. The method was found to be reliable for signal-to-noise ratio, defined by the ratio of the standard deviation of the signal to that of the noise in this study, less than three. Finally, the random uncertainty of the error estimates was determined to be in the order of 10 to 30 % for the total flux error, depending on the conditions and method of estimation.Peer reviewe

Dental staining after doxycycline use in children

Background: The use of doxycycline has been avoided before 8 years of age due to known dental staining caused by tetracyclines, although doxycycline differs from classical tetracyclines in many ways. Doxycycline is still an important antimicrobial agent, but its dental safety is not well studied. Objectives: To examine the state of permanent teeth after doxycycline exposure in children,8 years of age. Methods: Details of doxycycline treatment were collected from medical records. After the eruption of permanent teeth the dental status was examined by an experienced paediatric dentist for detection of dental staining and enamel hypoplasia. The resulting dental photographs were evaluated by a second independent experienced paediatric dentist. Results: The mean age of 38 study subjects at the time of doxycycline treatment was 4.7 years (range 0.6-7.9 years, SD 2.3). The doxycycline dose was 10 mg/kg/day (varying from 8 to 10 mg/kg/day) for the first 2-3 days and 5mg/kg/day (varying from 2.5 to 10mg/kg/day) thereafter. The mean length of the treatment was 12.5days (SD 6.0) and ranged from 2 to 28 days. Tetracycline-like staining or enamel hypoplasia of developing teeth was detected in none of the subjects. Conclusions: Doxycycline treatment of small children does not seem to induce permanent tooth staining.Peer reviewe

Long-term nationwide trends in the treatment of and outcomes among pancreatic cancer patients

Publisher Copyright: © 2021 The AuthorsWhilst treatment modalities for pancreatic cancer patients have evolved in recent years, their impact on outcomes remains relatively unexamined on a national scale. We aimed to analyse changes in overall survival and trends in surgical and oncological treatments in pancreatic cancer patients diagnosed in the periods 2000 through 2008 and 2009 through 2016 in Finland. We collected data for pancreatic cancer patients diagnosed between 2000 and 2016, gathering data from the Finnish national registries on surgeries, oncological treatments and time of death. Follow-up continued through the end of 2018. We compared patients diagnosed between 2000 and 2008 to those diagnosed between 2009 through 2016. Our study comprised 14 712 pancreatic cancer patients. There was no significant change in the national resection rate (8.1% vs 8.0%, p = 0.690). In radical surgery patients, median survival improved from 20 months (95% confidence interval (CI) 18–22) to 28 months (CI 25–31) (p < 0.001), with 1-year survival ranging from 70% to 81%. In the no-surgery group, median survival slightly improved from 3.1 months (CI 3.0–3.3) to 3.3 months (CI 3.1–3.4) (p < 0.001). The proportion of radical surgery patients receiving preoperative oncological treatment increased from 4% to 13% (p < 0.001) and only postoperative treatment from 25% to 47% (p < 0.001). Whilst the resection rate did not increase, the prognosis of pancreatic cancer patients improved, particularly amongst radical surgery patients resulting most likely from the fact that a larger proportion of patients receive more effective oncological treatments.Peer reviewe

Multi-year methane ebullition measurements from water and bare peat surfaces of a patterned boreal bog

We measured methane ebullition from a patterned boreal bog situated in the Siikaneva wetland complex in southern Finland. Measurements were conducted on water (W) and bare peat surfaces (BP) in three growing seasons (2014-2016) using floating gas traps. The volume of the trapped gas was measured weekly, and methane and carbon dioxide (CO2) concentrations of bubbles were analysed from fresh bubble samples that were collected separately. We applied a mixed-effect model to quantify the effect of the environmental controlling factors on the ebullition. Ebullition was higher from W than from BP, and more bubbles were released from open water (OW) than from the water's edge (EW). On average, ebullition rate was the highest in the wettest year ( 2016) and ranged between 0 and 253 mg m(-2) d(-1) with a median of 2 mg m(-2) d(-1), 0 and 147 mg m(-2) d(-1) with a median of 3 mg m(-2) d(-1), and 0 and 186 mg m(-2) d(-1) with a median of 28 mg m(-2) d(-1) in 2014, 2015, and 2016, respectively. Ebullition increased together with increasing peat temperature, weekly air temperature sum and atmospheric pressure, and decreasing water table (WT). Methane concentration in the bubbles released from W was 15-20 times higher than the CO2 concentration, and from BP it was 10 times higher. The proportion of ebullition fluxes upscaled to ecosystem level for the peak season was 2 %-8 % and 2 %- 5 % of the total flux measured with eddy covariance technique and with chambers and gas traps, respectively. Thus, the contribution of methane ebullition from wet non-vegetated surfaces of the bog to the total ecosystem-scale methane emission appeared to be small.Peer reviewe

Calibrating the sqHIMMELI v1.0 wetland methane emission model with hierarchical modeling and adaptive MCMC

Estimating methane (CH4) emissions from natural wetlands is complex, and the estimates contain large uncertainties. The models used for the task are typically heavily parameterized and the parameter values are not well known. In this study, we perform a Bayesian model calibration for a new wetland CH4 emission model to improve the quality of the predictions and to understand the limitations of such models. The detailed process model that we analyze contains descriptions for CH4 production from anaerobic respiration, CH4 oxidation, and gas transportation by diffusion, ebullition, and the aerenchyma cells of vascular plants. The processes are controlled by several tunable parameters. We use a hierarchical statistical model to describe the parameters and obtain the posterior distributions of the parameters and uncertainties in the processes with adaptive Markov chain Monte Carlo (MCMC), importance resampling, and time series analysis techniques. For the estimation, the analysis utilizes measurement data from the Siikaneva flux measurement site in southern Finland. The uncertainties related to the parameters and the modeled processes are described quantitatively. At the process level, the flux measurement data are able to constrain the CH4 production processes, methane oxidation, and the different gas transport processes. The posterior covariance structures explain how the parameters and the processes are related. Additionally, the flux and flux component uncertain-ties are analyzed both at the annual and daily levels. The parameter posterior densities obtained provide information regarding importance of the different processes, which is also useful for development of wetland methane emission models other than the square root HelsinkI Model of MEthane buiLd- up and emIssion for peatlands (sqHIMMELI). The hierarchical modeling allows us to assess the effects of some of the parameters on an annual basis. The results of the calibration and the cross validation suggest that the early spring net primary production could be used to predict parameters affecting the annual methane production. Even though the calibration is specific to the Siikaneva site, the hierarchical modeling approach is well suited for larger-scale studies and the results of the estimation pave way for a regional or global- scale Bayesian calibration of wetland emission models.Peer reviewe

Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements

Peer reviewe

Quantifying the uncertainty of eddy covariance fluxes due to the use of different software packages and combinations of processing steps in two contrasting ecosystems

We have carried out an inter-comparison between EddyUH and EddyPro (R), two public software packages for post-field processing of eddy covariance data. Datasets including carbon dioxide, methane and water vapour fluxes measured over 2 months at a wetland in southern Finland and carbon dioxide and water vapour fluxes measured over 3 months at an urban site in Helsinki were processed and analysed. The purpose was to estimate the flux uncertainty due to the use of different software packages and to evaluate the most critical processing steps, determining the largest deviations in the calculated fluxes. Turbulent fluxes calculated with a reference combination of processing steps were in good agreement, the systematic difference between the two software packages being up to 2.0 and 6.7% for half-hour and cumulative sum values, respectively. The raw data preparation and processing steps were consistent between the software packages, and most of the deviations in the estimated fluxes were due to the flux corrections. Among the different calculation procedures analysed, the spectral correction had the biggest impact for closed-path latent heat fluxes, reaching a nocturnal median value of 15% at the wetland site. We found up to a 43% median value of deviation (with respect to the run with all corrections included) if the closed-path carbon dioxide flux is calculated without the dilution correction, while the methane fluxes were up to 10% lower without both dilution and spectroscopic corrections. The Webb-Pearman-Leuning (WPL) and spectroscopic corrections were the most critical steps for open-path systems. However, we found also large spectral correction factors for the open-path methane fluxes, due to the sensor separation effect.Peer reviewe