1,721,092 research outputs found
Ageing of biomass burning organic aerosol in the FORTH atmospheric simulation chamber: chemical characterization by H-NMR
No full textWith the aim of identifying biomass burning (BB) SOA formation pathways, we performed ageing experiments of BB primary emissions at the FORTH Atmospheric-Simulation-Chamber in Patras, Greece. Different biofuels were employed using the most common types in Greece: olive-tree logs and pellets (residuals of pine-wood).
SOA formation was investigated under different conditions in term of oxidants (OH or NO3 radicals), photochemical conditions (illumination vs. dark), and relative humidity (up to 80%) in order to simulate both diurnal and nocturnal chemical ageing and assess the effects of humidity on SOA condensation and chemical transformation. The evolution of organic aerosol was monitored using a HR-ToF-AMS, while filter samples were collected for offline chemical characterization of the water-soluble organic fraction (WSOC) by means of proton-Nuclear Magnetic Resonance (H-NMR) spectroscopy.
H-NMR spectra of fresh and aged samples showed considerable variability between experiments. High relative humidity demonstrated to strongly influence the chemical features of aged BBOA
Chemical evolution of primary and formation of secondary biomass burning aerosols during daytime and nighttime
Full text linkOrganic matter (OM) can constitute more than half of
fine particulate matter (PM) and affect climate and
human health. Natural and man-made biomass burning
is an important contributor to primary and secondary
OM (POA and SOA) with an increasing trend.
Aerosol mass spectrometry (AMS) and Fourier
transform infrared spectroscopy (FTIR) are two
complementary methods of identifying the complex
chemical composition of OM in terms of mass fragments
and functional groups, respectively. AMS offers a
relatively higher temporal resolution compared to FTIR
(performed on PTFE filters). However, the interpretation
of AMS mass spectra remains complicated due to the
extensive molecular fragmentation.
In this study, we used collocated AMS and FTIR
measurements to better understand the evolution of
biomass burning POA and SOA due to different
mechanisms of chemical aging (e.g., homogeneous gasphase
oxidation and heterogeneous reactions). Primary
emissions from wood and pellet stoves were injected
into a 10 m3 environmental chamber located at the
Center for Studies of Air Qualities and Climate Change (CSTACC)
at ICE-HT/FORTH. Primary emissions were aged
using hydroxyl and nitrate radicals with atmospherically
relevant exposures. PM1 was analyzed by a highresolution
time-of-flight (HR-ToF) and was also collected
on PTFE filters over 20-minute periods before and after
aging for off-line FTIR analysis.
AMS and FTIR measurements agreed well with
regards to the concentration of OM and some biomass
burning tracers (levoglucosan and lignin; Yazdani A.,
2020b) and the OM:OC ratio. Chamber wall loss rates
were estimated using AMS OM concentration and were
used to split the contribution of POA and SOA. The
estimated FTIR and AMS spectra of SOA produced by
reactions of biomass burning volatile organic compounds
(VOCs) with OH were found to have prominent acid
signatures. Organonitrates, on the other hand, appeared
to be important for SOA produced by the nitrate radical.
We found that with continued aging, SOA evolves and
becomes similar to the oxygenated OA (OOA) in the
atmosphere. We also found that POA composition also
evolves with aging. Our estimates show that up to 10 %
of POA mass undergoes aging. Biomass burning tracers
such as lignin and levoglucosan in addition to
hydrocarbons are among the POA compounds that are
lost the most in biomass burning POA (up to 6 times more
than OM decrease due to chamber wall losses; Fig. 1).
This diminution is observed for both semi-volatile
(levoglucosan and hydrocarbons) and non-volatile
(lignin) POA species, implying the importance of gasparticle
partitioning, heterogeneous reactions, and
photolysis for POA evolution in the atmosphere. This
result can be important since chemical transport models
usually do not consider POA heterogeneous reactions.
Figure 1. Trends of individual AMS mass fragments (with
contribution to OM> 0.3 %) during aging with UV
(starting from time zero). All mass fragments have been
normalized by their concentration before the with start
of aging and corrected for the chamber wall losses.
Important mass fragments are shown in color.
This work was supported by the project PyroTRACH (ERC-
2016-COG) funded from H2020-EU.1.1. - Excellent
Science - European Research Council (ERC), project ID
726165 and funding from the Swiss National Science
Foundation (200021_172923).
References
Yazdani, A., Dudani, N., Takahama, S., Bertrand, A.,
Prévôt, A. S. H., El Haddad, I., and Dillner, A. M.:
Characterization of Primary and Aged Wood Burning and
Coal Combustion Organic Aerosols in Environmental
Chamber and Its Implications for Atmospheric Aerosols,
Atmospheric Chemistry and Physics Discussions, pp. 1–
32
Differentiating between primary and secondary organic aerosols of biomass burning in an environmental chamber with FTIR and AMS
Full text linkFine particulate matter (PM) affects visibility, climate and public health. Organic matter (OM), which is hard to characterize due to its complex chemical composition, can constitute more than half of the PM. Biomass burning from residential wood burning, wildfires, and prescribed burning is a major source of OM with an ever-increasing importance.
Aerosol mass spectrometry (AMS) and Fourier transform infrared spectroscopy (FTIR) are two complementary methods of identifying the chemical composition of OM. AMS measures the bulk composition of OM with relatively high temporal resolution but provides limited parent compound information. FTIR, carried out on samples collected on Teflon filters, provides detailed functional groupinformation at the expense of relatively low temporal resolution.
In this study, we used these two methods to better understand the evolution of biomass burning OM in the atmosphere with aging. For this purpose, primary emissions from wood and pellet stoves were injected into the Center for Studies of Air Qualities and Climate Change (C-STACC) environmental chamber at ICE-HT/FORTH. Primary emissions were aged using hydroxyl and nitrate radicals (with atmospherically relevant exposures) simulating atmospheric day-time and night-time oxidation. A time-of-flight (ToF) AMS reported the composition of non-refractory PM1 every three minutes and PM1 was collected on PTFE filters over 20-minute periods before and after aging for off-line FTIR analysis.
We found that AMS and FTIR measurements agreed well in terms of measured OM mass concentration, the OM:OC ratio, and concentration of biomass burning tracers – lignin and levoglucosan. AMS OM concentration was used to estimate chamber wall loss rates which were then used separate the contribution of primary and secondary organic aerosols (POA and SOA) to the aged OM. AMS mass spectra and FTIR spectra of biomass burning SOA and estimates of bulk composition were obtained by this procedure. FTIR and AMS spectra of SOA produced by OH oxidation of biomass burning volatile organic compounds (VOCs) were dominated by acid signatures. Organonitrates, on the other hand, appeared to be important in the SOA aged by the nitrate radical. The spectra from the two instruments also indicated that the signatures of certain compounds such as levoglucosan, lignin and hydrocarbons, which are abundant in biomass burning POA, diminish with aging significantly more than what can be attributed to chamber wall losses. The latter suggests biomass burning POA chemical composition might change noticeably due to heterogeneous reactions or partitioning in the atmosphere. Therefore, the common assumption of stable POA composition is only partially true. In addition, more stable biomass burning tracers should be used to be able to identify highly aged biomass burning aerosols in the atmosphere
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Functional group analysis of organic particulate matter from primary and aged biomass burning emissions in the FORTH environmental chamber with infrared spectroscopy
No full textBiomass burning from residential wood burning, wildfires, and prescribed burning is a major source of organic matter (OM). Aerosol mass spectrometry (AMS) and Fourier transform infrared spectroscopy (FT-IR) are common methods of characterizing OM. AMS possesses a high temporal resolution and FT-IR, carried out mostly on PTFE filters, provides detailed functional group information.
We utilized AMS and FT-IR to investigate the effects of aging on the chemical composition and concentration of OM from wood and pellet burning. Primary emissions were injected into the an environmental and aged using UV light or the nitrate radical (in high- and low-humidity conditions) to simulate day-time and night-time oxidation processes in the atmosphere.
Estimates of OM from AMS and FT-IR agree well, both detecting an increased O:C after aging. Mid-infrared spectroscopy, shows distinct functional group compositions (hence oxidation pathways) for aged biomass burning aerosols with UV light and in dark conditions
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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