Flux and concentration measurements of carbon dioxide and ozone in a forested environment

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Sammanfattning

This thesis compiles the setup and characteristics of the measurement systems for CO2, H2O vapour and O3 eddy-covariance (EC) flux and vertical concentration profile, and their calibration arrangements at the SMEAR II station of the University of Helsinki. A commercial chemiluminescence O3 analyser operating on a liquid reagent solution was modified to improve its suitability and reliability in long term EC flux measurements. Fluxes of CO2 and O3 were also determined with the flux-profile method relating the fluxes to the observed concentration profiles. The EC and the flux-profile methods were inter-compared and their performances were evaluated. A separate measurement system utilising a commercial, low cost Non-dispersive Infrared-absorption analyser and incorporating an automatic calibration system for measuring atmospheric CO2 mole fraction was developed in the thesis. The performance of the system was evaluated and its measurement accuracy was determined in comparisons to reference standards. The measured CO2 mole fraction data was compared with the results of an independent atmospheric transport simulation (MACC-II) for period November 2006–December 2011. The modifications made to the reagent liquid flow system improved the reliability of the EC O3 analyser. The fluxes measured with the eddy-covariance and flux-profile method agreed during daytime under unstable conditions. At night-time the flux-profile method estimated higher respiration of CO2 and stronger deposition of O3, but no apparent reason for over- or underestimation by either method was identified. Night-time eddy-covariance fluxes had a specious dependence on turbulence even after accounting for storage flux. Additionally the chemical sink strength was evaluated negligible also for O3. Accounting for vertical advection flux removed the dependencies. However, while accounting for the vertical advection flux resulted in invariance of both net ecosystem exchange (NEE) of CO2 and deposition rate of O3 on turbulence intensity, the importance for estimating e.g. NEE by different ways at other flux tower sites was stressed. The atmospheric CO2 mole fraction measurement system had an accuracy of 0.3–0.4 µmol mol-1, an operating ratio of 99 % and its data coverage was 95 % during the comparison period. The trend and phase of the modelled and measured atmospheric CO2 mole fraction data, on the average 390 µmol mol-1, were observed to generally agree and the average bias of the simulation, –0.2 µmol mol-1, was within the measurement accuracy. The instrumentation fulfilled the set requirements of accuracy and continuous operation, and the result of the comparison implied that the CO2 mole fraction data from the SMEAR II station would clearly have the potential to be assimilated in the MACC-II simulations and thus improving their accuracy.
Bidragets titel på inmatningsspråkHiilidioksidin ja otsonin vuo- ja pitoisuusmittaukset metsäympäristössä
Originalspråkengelska
Tilldelande institution
  • Helsingfors universitet
Handledare
  • Vesala, Timo, Handledare
  • Reissell, Anni Kaarina, Handledare
  • Petäjä, Tuukka, Handledare
Tilldelningsdatum3 nov 2017
UtgivningsortHelsinki
Förlag
Tryckta ISBN978-952-7091-90-6
Elektroniska ISBN978-952-7091-91-3
StatusPublicerad - 3 nov 2017
MoE-publikationstypG5 Doktorsavhandling (artikel)

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  • 1172 Miljövetenskap
  • 4112 Skogsvetenskap

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