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Observational Studies of Organic Aerosol Formation from Anthropogenic Activities : A Mass Spectrometric Approach
No full textHuman activity has affected the atmosphere in various ways by increased emissions of different gas and particle phase compounds from anthropogenic sources. Secondary organic aerosol (SOA) is formed by the uptake of low-volatility vapors to particles. One of the main precursors for these low-volatility vapors is volatile organic compounds (VOCs), that through different atmospheric oxidation processes form condensable vapors. While aerosol particles are known to affect both Earth’s climate and air quality, the extensive complexity of both gas and particle phase reactions contributing to SOA makes this an interesting, although sometimes challenging, process to study.
The objectives of this thesis were to improve our understanding of SOA formation that is affected by human activities. I mainly used different mass spectrometric techniques to explore SOA formation in both laboratory experiments as well as through field studies. In practice, I studied the role of particulate organic nitrate (pON) in a boreal forest, SOA formation from alkanes, and the effect of using germicidal ultraviolet (GUV) light on in-door air quality. pON and alkane SOA are directly linked to human activity and originate primarily from anthropogenic NOx and alkane emissions, respectively. Additionally, as the commonly used Aerosol Mass Spectrometer (AMS) was one of the main instruments in this thesis, I investigated how AMS data analysis is affected by different choices made during data processing.
We observed that in the boreal forest, with only minor anthropogenic influence, pON con-tributed approximately 10 % of the total observed aerosol mass, and the background ni-trate aerosol mainly originated from pON. Through laboratory studies, using an oxidation flow reactor, we measured SOA yields of seven C10 alkanes and their oxygenated deriva-tives, where cyclic compounds (cis-decalin and n-butylcyclohexane) and decanal showed the highest yields, with maximum yields ranging from 16 to 44 %. Furthermore, we ob-served a dramatic increase in particle number concentration, as well as an increase in a huge number of gas phase compounds, in an indoor environment when using a commercial GUV-device for disinfection.
The results presented in this thesis improve our understanding of the effect of human ac-tivity on aerosol formation, and support the idea of anthropogenic SOA being a key aerosol component in different environments. The novelty of our indoor air quality measure-ments during GUV operation, the use of which increased in the wake of the COVID-19 pandemic, shows the importance of using the latest scientific methods to address new, unexpectedly arising questions.Mänsklig aktivitet har påverkat vår atmosfär på flera sätt genom ökade utsläpp från olika källor av gaser och partiklar. Sekundär organisk aerosol (SOA, engelska ”secondary organic aerosol”) bildas då ångor med låg flyktighet kondenserar på aerosolpartiklar. Dessa lågflyktiga ångor uppkommer främst genom oxidering av lättflyktiga organiska föreningar (VOC, engelska ”volatile organic compound”). Aerosolpartiklar är kända för att påverkar både jordens klimat och luftkvalitet, men komplexiteten hos de reaktionerna som bildar SOA gör detta till ett intressant, dock ibland utmanande, forskningsområde.
Syftet med denna avhandling var att förbättra vår förståelse av SOA-bildning som påverkas av mänsklig aktivitet. Basen för forskningen var olika masspektrometri-metoder som utnyttjades både i laboratorieexperiment samt fältstudier.
I praktiken undersökte jag rollen av partikulärt organiskt nitrat (pON, engelska ”particulate organic nitrate”) i det norra barrskogsbältet, SOA-bildning från alkaner och hur användningen av bakteriedödande ultraviolett ljus (GUV, engelska ”germicidial ultraviolet”) påverkar luftkvalitén inomhus. pON- och alkan-SOA är direkt kopplade till mänsklig aktivitet och härstammar främst från antropogena NOx- och alkanutsläpp. Utöver detta, undersökte jag hur data från aerosolmasspektrometern (AMS, engelska ”Aerosol Mass Spectrometer”), ett av de viktigaste instrumenten i denna avhandling, kan analyseras på olika sätt och hur det påverkas av olika val under databehandlingen.
Enligt våra observationer, vid en mätstation i det norra barrskogsbältet med endast liten antropogen påverkan, bidrog pON med ungefär 10% av den totala aerosolmassan samt att bakgrundsnitrataerosolen härstammar främst från pON. Vi mätte också hur mycket SOA sju olika C10-alkaner och deras derivat bildar. Dessa laboratoriemätningar utfördes med hjälp av en oxidationsflödesreaktor, och den högsta SOA bildningen kom från cykliska föreningar samt dekanal. Dessutom observerade vi en dramatisk ökning i koncentrationen av små partiklar, samt en ökning av ett stort antal gasfasföreningar i en inomhusmiljö då en kommersiell GUV-enhet användes för desinfektion.
Resultaten som presenteras i denna avhandling förbättrar vår förståelse av effekten av mänsklig aktivitet på aerosolbildningen samt stödjer idén om att antropogen SOA är en viktig komponent i olika förhållanden och miljöer. Våra unika inomhusluftkvalitetsmätningar med GUV-förhållanden, vars användning ökade kraftigt på grund av COVID-19-pandemin, demonstrerar vikten av att använda de senaste vetenskapliga metoderna för att ta itu med nya, oväntat uppkomna frågor.ei saavutettav
Fragmentation patterns of particulate organic nitrates in an Aerosol Mass Spectrometer
Get PDFAtmospheric aerosols affect the Earth's radiative balance, visibility and human health. Therefore the formation processes and growth of these particles are important and should be studied to understand how human and natural processes affects these processes. One poorly understood and relatively little studied part of aerosols is particulate organic nitrates (pONs). These pONs are mostly formed during nighttime when NOx, mainly emitted from fossil fuel combustion and industrial processes, and volatile organic compounds (VOCs), from both natural and anthropogenic sources, reacts in the atmosphere. The quantification of these pONs is still hard due to instrumental restrictions, although much improvement has happened during recent years. One main reason for these challenges is the difficulty to separate inorganic nitrates from organic nitrates with real-time instruments.
During this work, we generated pure pON in well controlled laboratory conditions and sampled it with an Aerosol Mass Spectrometer (AMS), an instrument widely used for measuring the chemical composition of atmospheric aerosols. We used four different pON precursors to generate pON. I investigated the fragmentation patterns of pON detected by the AMS, utilizing the high resolution of the newest model of the AMS. As older versions of the AMS has difficulties to separate nitrate-containing organic fragments due to lower resolution than the AMS I used, I was able to study pON mass spectrum with better resolution than anyone before me. I found mass spectral differences for the different pON precursors, and was able to find unique fragments for some of the pON precursors that possibly can be used as marker fragments
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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