Disjunct eddy covariance measurements of volatile organic compound fluxes using proton transfer reaction mass spectrometry

Volatile organic compounds (VOCs) are emitted into the atmosphere from natural and anthropogenic sources, vegetation being the dominant source on a global scale. Some of these reactive compounds are deemed major contributors or inhibitors to aerosol particle formation and growth, thus making VOC measurements essential for current climate change research. This thesis discusses ecosystem scale VOC fluxes measured above a boreal Scots pine dominated forest in southern Finland. The flux measurements were performed using the micrometeorological disjunct eddy covariance (DEC) method combined with proton transfer reaction mass spectrometry (PTR-MS), which is an online technique for measuring VOC concentrations. The measurement, calibration, and calculation procedures developed in this work proved to be well suited to long-term VOC concentration and flux measurements with PTR-MS. A new averaging approach based on running averaged covariance functions improved the determination of the lag time between wind and concentration measurements, which is a common challenge in DEC when measuring fluxes near the detection limit. The ecosystem scale emissions of methanol, acetaldehyde, and acetone were substantial. These three oxygenated VOCs made up about half of the total emissions, with the rest comprised of monoterpenes. Contrary to the traditional assumption that monoterpene emissions from Scots pine originate mainly as evaporation from specialized storage pools, the DEC measurements indicated a significant contribution from de novo biosynthesis to the ecosystem scale monoterpene emissions. This thesis offers practical guidelines for long-term DEC measurements with PTR-MS. In particular, the new averaging approach to the lag time determination seems useful in the automation of DEC flux calculations. Seasonal variation in the monoterpene biosynthesis and the detailed structure of a revised hybrid algorithm, describing both de novo and pool emissions, should be determined in further studies to improve biological realism in the modelling of monoterpene emissions from Scots pine forests. The increasing number of DEC measurements of oxygenated VOCs will probably enable better estimates of the role of these compounds in plant physiology and tropospheric chemistry. Keywords: disjunct eddy covariance, lag time determination, long-term flux measurements, proton transfer reaction mass spectrometry, Scots pine forests, volatile organic compoundsIlmakehään haihtuu orgaanisia yhdisteitä sekä luonnosta että ihmisen toiminnan seurauksena. Osa näistä yhdisteistä vaikuttaa aerosolihiukkasten muodostukseen ja kasvuun, joiden parempi tuntemus on edellytys ilmastomallien ja -ennusteiden kehitykselle. Tämän väitöskirjan aihe on haihtuvien orgaanisten yhdisteiden (volatile organic compounds, VOCs) päästöjen mittaaminen ajoittaisen näytteenoton kovarianssimenetelmällä (disjunct eddy covariance, DEC) protoninsiirtoreaktiomassaspektrometriaa (proton transfer reaction mass spectrometry, PTR-MS) käyttäen. Tarkasteltavat mikrometeorologiset ekosysteemitason päästömittaukset tehtiin mäntyvaltaisen metsän yläpuolella Helsingin yliopiston SMEAR II -asemalla Hyytiälässä. Työssä kehitettiin mittaus-, kalibrointi- ja laskentamenetelmiä pitkäaikaisiin ja ympärivuorokautisiin DEC-PTR-MS-mittauksiin. Kehitetyt menetelmät paransivat mittausten luotettavuutta ja helpottivat niiden käytännön toteutusta. Uusi kovarianssifunktion liukuvaan keskiarvoon perustuva menetelmä pienensi tuuli- ja pitoisuusmittauksen välisen viiveajan määrittämiseen liittyvää virhettä. Metanolin, asetaldehydin, asetonin ja monoterpeenien päästöt mäntymetsästä olivat merkittäviä. Hapettuneet yhdisteet (metanoli, asetaldehydi ja asetoni) muodostivat noin puolet kokonaispäästöistä. Vastoin yleistä oletusta, jonka mukaan männyn monoterpeenipäästöt johtuvat pääosin haihtumisesta pihkatiehyistä, huomattava osa ekosysteemitason monoterpeenipäästöistä oli todennäköisesti peräisin suoraan biosynteesistä. Tämä työ tarjoaa erityisesti laskentamenetelmien automatisointia edistäviä suosituksia DEC-PTR-MS-mittauksiin. Tulevissa tutkimuksissa mäntymetsien monoterpeenipäästöjä kuvaavia algoritmeja on syytä uudistaa siten, että ne huomioivat monoterpeenien haihtumisen ohella myös suoraan monoterpeenisynteesistä aiheutuvat päästöt entistä paremmin. Lisääntyvä mittausaineisto hapettuneiden yhdisteiden päästöistä voi auttaa selventämään näiden yhdisteiden merkitystä kasvifysiologiassa ja troposfäärin kemiassa

A source-orientated approach for estimating daytime concentrations of biogenic volatile organic compounds in an upper layer of a boreal forest canopy

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Continuous flux measurements of VOCs using PTR-MS — reliability and feasibility of disjunct-eddy-covariance, surface-layer-gradient, and surface-layer-profile methods

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Ruokohelven polttoaineketjun kehittäminen liiketoimintamahdollisuuksien parantamiseksi

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Role of de novo biosynthesis in ecosystem scale monoterpene emissions from a boreal Scots pine forest

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Winter to spring transition and diurnal variation of VOCs in Finland at an urban background site and a rural site

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New instrument for measuring atmospheric concentrations of non-OH oxidants of SO2

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Monoterpene pollution episodes in a forest environment : indication of anthropogenic origin and association with aerosol particles

We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol

Concentrations and fluxes of biogenic volatile organic compounds above a Mediterranean macchia ecosystem in western Italy

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Sources of long-lived atmospheric VOCs at the rural boreal forest site, SMEAR II

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