Atmospheric sulfur compounds in the troposphere and stratosphere measured with an atomic emission detector

Carbonyl sulfide (OCS) plays a crucial role in the Earth’s sulfur budget. Globally OCS is the predominant reduced sulfur species in the Earth’s atmosphere with typical tropospheric mixing ratios of around 500 ppt. During volcanically quiescent periods OCS controls the atmospheric sulfur budget within the troposphere and stratosphere, and the upward transport governs the background stratospheric aerosol loading due to its long atmospheric lifetime. The stratospheric sulfate aerosol layer (Junge layer) affects the global radiative balance, as sulfate aerosol particles scatter a fraction of incoming solar energy back to space. Sulfate particles can also act as cloud condensation nuclei (CCN) and ice nuclei (IN), thus further increasing the albedo of the Earth. Furthermore, OCS also acts as a climate forcing gas, absorbing longwave outgoing infrared radiation. Research into OCS has a long history, but nevertheless the atmospheric OCS budget remains unbalanced. Therefore, improving knowledge of OCS sources, and sink processes is essential for improving current models and thereby for accurate future climate forecasts. Throughout this PhD work a novel analytical system was developed to measure volatile organic compounds (VOCs), with primary focus on organosulfur species. The system consists of a gas phase cryogenic pre-concentration system (Entech), gas chromatographic (GC) separation and 3rd generation atomic emission detection (AEDIII), hence termed Entech-GC-AEDIII. The setup and performance of this newly established system is demonstrated. The Entech-GC-AEDIII enables various VOC measurement, including organosulfur species, non-methane hydrocarbons (NMHC), halogenated compounds, volatile nitrogen compounds, monoterpenes etc. This is the first instrument report of a gas phase air sample analysis method with an AED instrument. Whole air samples (WAS) were collected globally from the upper troposphere / lowermost stratosphere (UT/LMS) region onboard a Lufthansa Airbus A340-600 IAGOS-CARIBIC passenger aircraft into flasks by a fully automated system. The post-flight flask analyses were conducted between December 2015 and December 2018 by the automated Entech-GC-AEDIII system in a laboratory. From the OCS measurements a global OCS lifetime of 2.1 ± 1.3 years, and a significantly longer stratospheric lifetime of 47 ± 16 years were determined. Furthermore, a flux of 118 ± 39 Gg (S) yr-1 of OCS from the troposphere into the stratosphere was estimated, and the stratospheric sink estimate yielded 44 – 90 Gg (S) yr-1 of OCS. The 43% smaller sink serves as a 51 Gg (S) yr-1 estimate of the OCS fraction which is transported back from the stratosphere to the troposphere. The global 3D ECHAM5 / MESSy Atmospheric Chemistry (EMAC) model was used to run the numerical calculations and sampled at the CARIBIC flight paths. A comparison between CARIBIC observations and EMAC model simulations led to a conclusion that the EMAC model substantially overestimates OCS MRs in the upper atmosphere. A first of its kind measurement campaign with the new Entech-GC-AEDIII detector was conducted in a Finnish boreal forest at the Hyytiälä measurement station in September 2016. The boreal forests comprise 33% of the Earth’s forest cover, making it the second largest biome in the world. Therefore, it is an essential component of the atmospheric biosphere – geosphere interface. The OCS measurements demonstrated the boreal forest as a strong vegetative sink for OCS, which could be one of the reasons for the discrepancy between the EMAC model and CARIBIC observations in the tropopause region. Furthermore, the nighttime uptake of OCS was analyzed, concluding the light independence of OCS fixing carbonic anhydrase (CA) enzyme.Carbonylsulfid (OCS) spielt eine entscheidende Rolle im Schwefelhaushalt der Erde. OCS ist die am meisten vorkommende reduzierte Schwefelverbindung in der Erdatmosphäre mit einem Anteil von circa 500 pptv. In Epochen mit geringerer vulkanischer Aktivität wird der atmosphärische Schwefelhaushalt in der Stratos- und Troposphäre durch OCS dominiert und aufgrund seiner langen atmosphärischen Lebensdauer hat OCS einen großen Anteil an der stratosphärischen Aerosol Bildung. Die stratosphärische Sulfat-Aerosolschicht (Junge-Schicht) beeinflusst die globale Strahlungsbilanz, da Sulfat-Aerosolpartikel einen kleinen Teil der einfallenden Sonnenenergie in den Weltraum streuen und auch als Wolkenkondensationskeime (CCN) und Eisnukleationskerne (IN) wirken können, wodurch sie weiter die Albedo der Erde erhöhen. Darüber hinaus fungiert OCS auch als Klima Gas, das die von der Erde zurückgestrahlte langwellige Infrarotstrahlung absorbiert. Die Erforschung von OCS hat eine lange Geschichte, dennoch ist der atmosphärische OCS-Kreislauf noch nicht aufgeklärt. Daher ist die Erforschung der Prozesse von OCS, speziell Quellen und Senken, und das atmosphärische Budget für aktuelle Modellverbesserungen und genaue künftige Klimavorhersagen unerlässlich. In dieser Doktorarbeit wurde ein neuartiges Analysesystem entwickelt, um flüchtige organische Verbindungen (VOCs) zu messen, wobei der Schwerpunkt auf Organoschwefelverbindungen lag. Das System besteht aus einem kryogenen Gasphasen-Vorkonzentrationssystem (Entech), einer gaschromatographischen Trennung (GC) und einem Atomemissionsspektrometer der dritten Generation (AEDIII), der im Folgenden Entech-GC-AEDIII genannt wird. Aufbau und Leistung dieses neu etablierten Systems werden erklärt und demonstriert. Der Entech-GC-AEDIII ermöglicht die Messung verschiedener VOCs, einschließlich Organoschwefelspezies, Nicht-Methan-Kohlenwasserstoffe (NMHC), halogenierte Verbindungen, flüchtige Stickstoffverbindungen, Monoterpene usw. Dies ist der erste Instrumentenbericht einer Gasphasen-Probenanalyse mit einem AED-Instrument. Luftproben (WAS) wurden an Bord eines Lufthansa Airbus A340-600 IAGOS-CARIBIC-Passagierflugzeugs mit einem einer vollständig automatisierten Kollektor gesammelt. Die Proben umspannen ein weltweites Netz und wurden in der oberen Troposphäre / der untersten Stratosphäre (UT/LMS) gesammelt. Die Probenanalysen nach dem Flug wurden zwischen Dezember 2015 und Dezember 2018 vom automatisierten Entech-GC-AEDIII-System in einem Labor durchgeführt. Aus den OCS-Messungen wurden eine globale OCS-Lebensdauer von 2,1 ± 1,3 Jahren und eine signifikant längere Lebensdauer in der Stratosphäre von 47 ± 16 Jahren ermittelt. Darüber hinaus wurde ein Fluss von 118 ± 39 Gg (S) yr-1 von OCS aus der Troposphäre in die Stratosphäre abgeschätzt, und die Schätzung der Stratosphärensenke ergab 44 - 90 Gg (S) yr-1. Nach Abschätzung der OCS-Fraktion, baut die stratosphärische Senke ca. 51 Gg (S) yr-1 ab, die von der Stratosphäre in die Troposphäre zurücktransportiert wird. Das globale 3D-Modell ECHAM5 / MESSy Atmospheric Chemistry (EMAC) wurde für numerische Berechnungen verwendet und simuliert die Konzentrationen auf den CARIBIC-Flugstrecken. Ein Vergleich zwischen CARIBIC-Beobachtungen und EMAC-Modellsimulationen zeigt, dass das EMAC-Modell in der oberen Atmosphäre die OCS MRs wesentlich überschätzt. Eine weitere Messkampagne mit dem neuen Entech-GC-AEDIII-Detektor wurde im September 2016 in einem finnischen Borealwald an der Hyytiälä-Messstation durchgeführt. Die Borealwälder machen 33% der Waldfläche der Erde aus und sind damit das zweitgrößte Biom an Land. Die Wälder sind daher eine wichtige Schnittstelle für die atmosphärischen Bio-Geo-Emissionen. Die OCS-Messungen zeigen den Borealwald als starke vegetative Senke für OCS, was einer der Gründe für die Diskrepanz zwischen dem EMAC-Modell und den CARIBIC-Messungen in der Tropopause sein könnte. Darüber hinaus wurde die nächtliche Aufnahme von OCS untersucht, und somit die Lichtunabhängigkeit der OCS-Fixierung durch das Carboanhydrase (CA) gezeigt

Direct measurement of NO3 radical reactivity in a boreal forest

We present the first direct measurements of NO3 reactivity (or inverse lifetime, s(-1))in the Finnish boreal forest. The data were obtained during the IBAIRN campaign (Influence of Biosphere-Atmosphere Interactions on the Reactive Nitrogen budget) which took place in Hyytiala, Finland during the summer/autumn transition in September 2016. The NO3 reactivity was generally very high with a maximum value of 0.94 s(-1) and displayed a strong diel variation with a campaign-averaged nighttime mean value of 0.11 s(-1) compared to a daytime value of 0.04 s(-1). The highest nighttime NO3 reactivity was accompanied by major depletion of canopy level ozone and was associated with strong temperature inversions and high levels of monoterpenes. The daytime reactivity was sufficiently large that reactions of NO3 with organic trace gases could compete with photolysis and reaction with NO. There was no significant reduction in the measured NO3 reactivity between the beginning and end of the campaign, indicating that any seasonal reduction in canopy emissions of reactive biogenic trace gases was offset by emissions from the forest floor. Observations of biogenic hydrocarbons (BVOCs) suggested a dominant role for monoterpenes in determining the NO3 reactivity. Reactivity not accounted for by in situ measurement of NO and BVOCs was variable across the diel cycle with, on average, approximate to 30% "missing" during nighttime and approximate to 60% missing during the day. Measurement of the NO3 reactivity at various heights (8.5 to 25 m) both above and below the canopy, revealed a strong nighttime, vertical gradient with maximum values closest to the ground. The gradient disappeared during the daytime due to efficient vertical mixing.Peer reviewe

Alkyl nitrates in the boreal forest : formation via the NO3-, OH- and O-3-induced oxidation of biogenic volatile organic compounds and ambient lifetimes

The formation of alkyl nitrates in various oxidation processes taking place throughout the diel cycle can represent an important sink of reactive nitrogen and mechanism for chain termination in atmospheric photo-oxidation cycles. The low-volatility alkyl nitrates (ANs) formed from biogenic volatile organic compounds (BVOCs), especially terpenoids, enhance rates of production and growth of secondary organic aerosol. Measurements of the NO3 reactivity and the mixing ratio of total alkyl nitrates (6 ANs) in the Finnish boreal forest enabled assessment of the relative importance of NO3-, O-3- and OH-initiated formation of alkyl nitrates from BVOCs in this environment. The high reactivity of the forest air towards NO3 resulted in reactions of the nitrate radical, with terpenes contributing substantially to formation of ANs not only during the night but also during daytime. Overall, night-time reactions of NO3 accounted for 49% of the local production rate of ANs, with contributions of 21 %, 18% and 12% for NO3, OH and O-3 during the day. The lifetimes of the gas-phase ANs formed in this environment were on the order of 2 h due to efficient uptake to aerosol (and dry deposition), resulting in the transfer of reactive nitrogen from anthropogenic sources to the forest ecosystem.Peer reviewe

Pyruvic acid in the boreal forest : gas-phase mixing ratios and impact on radical chemistry

Pyruvic acid (CH3C(O)C(O)OH, 2-oxopropanoic acid) is an organic acid of biogenic origin that plays a crucial role in plant metabolism, is present in tropospheric air in both gas-phase and aerosol-phase, and is implicated in the formation of secondary organic aerosols (SOAs). Up to now, only a few field studies have reported mixing ratios of gas-phase pyruvic acid, and its tropospheric sources and sinks are poorly constrained. We present the first measurements of gas-phase pyruvic acid in the boreal forest as part of the IBAIRN (Influence of Biosphere–Atmosphere Interactions on the Reactive Nitrogen budget) field campaign in Hyytiälä, Finland, in September 2016. The mean pyruvic acid mixing ratio during IBAIRN was 96 pptv, with a maximum value of 327 pptv. From our measurements we estimated the overall pyruvic acid source strength and quantified the contributions of isoprene oxidation and direct emissions from vegetation in this monoterpene-dominated forested environment. Further, we discuss the relevance of gas-phase pyruvic acid for atmospheric chemistry by investigating the impact of its photolysis on acetaldehyde and peroxy radical production rates. Our results show that, based on our present understanding of its photochemistry, pyruvic acid is an important source of acetaldehyde in the boreal environment, exceeding ethane and propane oxidation by factors of ∼10 and ∼20.Pyruvic acid (CH3C(O)C(O)OH, 2-oxopropanoic acid) is an organic acid of biogenic origin that plays a crucial role in plant metabolism, is present in tropospheric air in both gas-phase and aerosol-phase, and is implicated in the formation of secondary organic aerosols (SOAs). Up to now, only a few field studies have reported mixing ratios of gas-phase pyruvic acid, and its tropospheric sources and sinks are poorly constrained. We present the first measurements of gas-phase pyruvic acid in the boreal forest as part of the IBAIRN (Influence of Biosphere-Atmosphere Interactions on the Reactive Nitrogen budget) field campaign in Hyytiala, Finland, in September 2016. The mean pyruvic acid mixing ratio during IBAIRN was 96 pptv, with a maximum value of 327 pptv. From our measurements we estimated the overall pyruvic acid source strength and quantified the contributions of isoprene oxidation and direct emissions from vegetation in this monoterpene-dominated forested environment. Further, we discuss the relevance of gas-phase pyruvic acid for atmospheric chemistry by investigating the impact of its photolysis on acetaldehyde and peroxy radical production rates. Our results show that, based on our present understanding of its photochemistry, pyruvic acid is an important source of acetaldehyde in the boreal environment, exceeding ethane and propane oxidation by factors of similar to 10 and similar to 20.Peer reviewe

Strong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere

Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m$^{-3}$, standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m$^{-3}$) with more than 100-fold enhanced peak values (up to ∼720 ng·m$^{-3}$). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h$^{-1}$ due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate

Real-Time Analysis of Ambient Organic Aerosols Using Aerosol Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (AeroFAPA-MS)

Organic compounds contribute to a major fraction of atmospheric aerosols and have significant impacts on climate and human health. However, because of their chemical complexity, their measurement remains a major challenge for analytical instrumentation. Here we present the development and characterization of a new soft ionization technique that allows mass spectrometric real-time detection of organic compounds in aerosols. The aerosol flowing atmospheric-pressure afterglow (AeroFAPA) ion source is based on a helium glow discharge plasma, which generates excited helium species and primary reagent ions. Ionization of the analytes occurs in the afterglow region after thermal desorption and produces mainly intact quasimolecular ions, facilitating the interpretation of the acquired mass spectra. We illustrate that changes in aerosol composition and concentration are detected on the time scale of seconds and in the ng m^–3 range. Additionally, the successful application of AeroFAPA-MS during a field study in a mixed forest region is presented. In general, the observed compounds are in agreement with previous offline studies; however, the acquisition of chemical information and compound identification is much faster. The results demonstrate that AeroFAPA-MS is a suitable tool for organic aerosol analysis and reveal the potential of this technique to enable new insights into aerosol formation, growth, and transformation in the atmosphere