The importance of sesquiterpene oxidation products for secondary organic aerosol formation in a springtime hemiboreal forest

Secondary organic aerosols (SOAs) formed from biogenic volatile organic compounds (BVOCs) constitute a significant fraction of atmospheric particulate matter and have been recognized to significantly affect the climate and air quality. Atmospheric SOA particulate mass yields and chemical composition result from a complex mixture of oxidation products originating from a diversity of BVOCs. Many laboratory and field experiments have studied SOA particle formation and growth in the recent years. However, a large uncertainty still remains regarding the contribution of BVOCs to SOA. In particular, organic compounds formed from sesquiterpenes have not been thoroughly investigated, and their contribution to SOA remains poorly characterized. In this study, a Filter Inlet for Gases and Aerosols (FI-GAERO) combined with a high-resolution time-of-flight chemical ionization mass spectrometer (CIMS), with iodide ionization, was used for the simultaneous measurement of gas-phase and particle-phase oxygenated compounds. The aim of the study was to evaluate the relative contribution of sesquiterpene oxidation products to SOA in a springtime hemiboreal forest environment. Our results revealed that monoterpene and sesquiterpene oxidation products were the main contributors to SOA particles. The chemical composition of SOA particles was compared for times when either monoterpene or sesquiterpene oxidation products were dominant and possible key oxidation products for SOA particle formation were identified for both situations. Surprisingly, sesquiterpene oxidation products were the predominant fraction in the particle phase in some periods, while their gas-phase concentrations remained much lower than those of monoterpene products. This can be explained by favorable and effective partitioning of sesquiterpene products into the particle phase. The SOA particle volatility determined from measured thermograms increased when the concentration of sesquiterpene oxidation products in SOA particles was higher than that of monoterpenes. Overall, this study demonstrates that sesquiterpenes may have an important role in atmospheric SOA formation and oxidation chemistry, in particular during the spring recovery period.Peer reviewe

Tsükliline elektrontransport taimedes : selle mõõtmine ning mehhanism

Väitekirja elektroonilist versioonist puuduvad väitekirjas sisalduvate publikatsioonide täistekstid.In plant photosynthesis, linear electron transport (LET) from H2O to NADP+ and to CO2 further on is coupled with transmembrane H+ transport supporting ATP synthesis. The stoichiometry of 3ATP/2NADPH = 12H+/4e- is the absolute requirement for CO2 reduction. For a half of a century it has been a common belief that violations of this stoichiometry are corrected by cyclic electron transport (CET) during which some electrons are cycling around photosystem I (PSI) in an H+ coupled way. Though CET was detected in plant leaves, its rate was never exactly quantified, as well the amount of CET-related ATP synthesis was not compared with the actual ATP needs. In this work CET rate was measured and the assumed ATP synthesis quantified in leaves under experimental conditions where the metabolic ATP consumption was reduced to minimum. Differently from the present common belief, CET rate is at maximum when ATP is at maximum and its additional synthesis is unnecessary. The conclusion is that CET is variably coupled with transmembrane H+ translocation. Therefore the new model of CET is developed to explain this situation.Taimede fotosünteesis on lineaarne elektrontransport (LET) H2O-lt NADPH+-le ja sealt edasi CO2-le seotud transmembraanse prootonite transpordiga, mis omakorda võimaldab ATP sünteesi. Stöhhiomeetria 3ATP/2NADPH = 12H+/4e- on ainuõige ATP sünteesi jaoks. Pool sajandit on kestnud üldine arusaam, et kõrvalekalded sellest stöhhiomeetriast korrigeeritakse tsüklilise elektrontranspordi (CET) poolt. CET kujutab endast elektrontransportahelat, kus mõned elektronid liiguvad ümber fotosüsteem I (PSI) selliselt, et võimaldavad ka prootonite transporti. Kuigi CETi on taimedes korduvalt mõõdetud, ei ole need mõõtmised olnud piisavalt täpsed ning neid ei ole võrreldud reaalse ATP tarbimisega elusas lehes. Antud töös mõõdeti CETi tingimustes, kus ATP tarve oli väga väike. Vastupidiselt oodatule oli CETi kiirus väga suur olukorras, kus ATPd sisuliselt ei tarbitudki. Seetõttu järeldati, et CET siiski ei transpordi prootoneid ning töötati välja uus mudel, mis kirjeldab saadud katsetulemusi nii, et ei minda vastuollu LETi funktsioneerimisega

Combined Acute Ozone and Water Stress Alters the Quantitative Relationships between O3 Uptake, Photosynthetic Characteristics and Volatile Emissions in Brassica nigra

Ozone (O3) entry into plant leaves depends on atmospheric O3 concentration, exposure time and openness of stomata. O3 negatively impacts photosynthesis rate (A) and might induce the release of reactive volatile organic compounds (VOCs) that can quench O3, and thereby partly ameliorate O3 stress. Water stress reduces stomatal conductance (gs) and O3 uptake and can affect VOC release and O3 quenching by VOC, but the interactive effects of O3 exposure and water stress, as possibly mediated by VOC, are poorly understood. Well-watered (WW) and water-stressed (WS) Brassica nigra plants were exposed to 250 and 550 ppb O3 for 1 h, and O3 uptake rates, photosynthetic characteristics and VOC emissions were measured through 22 h recovery. The highest O3 uptake was observed in WW plants exposed to 550 ppb O3 with the greatest reduction and poorest recovery of gs and A, and elicitation of lipoxygenase (LOX) pathway volatiles 10 min–1.5 h after exposure indicating cellular damage. Ozone uptake was similar in 250 ppb WW and 550 ppb WS plants and, in both treatments, O3-dependent reduction in photosynthetic characteristics was moderate and fully reversible, and VOC emissions were little affected. Water stress alone did not affect the total amount and composition of VOC emissions. The results indicate that drought ameliorated O3 stress by reducing O3 uptake through stomatal closure and the two stresses operated in an antagonistic manner in B. nigra

Combined acute ozone and water stress alters the quantitative relationships between O₃ uptake, photosynthetic characteristics and volatile emissions in Brassica nigra

Ozone and water stress effects on Brassica nigra volatile organic compounds emission (VOC) and photosynthetic characteristics. VOCs were collected on adsorbent cartridges and analyzed with GC-MS. Ozone exposures were 250 ppb O₃ for well-watered and 550 ppb O₃ for well-watered and water-stressed B. nigra plants.European Commission through European Research Council (advanced grant 322603, SIP-VOL+) and the European Regional Development Fund (Centre of Excellence EcolChange), and from the Estonian Research Council (team grant PRG537) and the Estonian University of Life Sciences (grant P180273PKTT)