| 1. |
- Gonzalez, N. J. D., et al.
(författare)
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Primary and secondary organics in the tropical Amazonian rainforest aerosols : chiral analysis of 2-methyltetraols
- 2014
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Ingår i: ENVIRON SCI-PROC IMP. - : Royal Society of Chemistry (RSC). - 2050-7887 .- 2050-7895. ; 16:6, s. 1413-1421
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Tidskriftsartikel (refereegranskat)abstract
- This work presents the application of a new method to facilitate the distinction between biologically produced (primary) and atmospherically produced (secondary) organic compounds in ambient aerosols based on their chirality. The compounds chosen for this analysis were the stereomers of 2-methyltetraols, (2R, 3S)- and (2S, 3R)-methylerythritol, (L- and D-form, respectively), and (2S, 3S)- and (2R, 3R)-methylthreitol (L- and D-form), shown previously to display some enantiomeric excesses in atmospheric aerosols, thus to have at least a partial biological origin. In this work PM10 aerosol fractions were collected in a remote tropical rainforest environment near Manaus, Brazil, between June 2008 and June 2009 and analysed. Both 2-methylerythritol and 2-methylthreitol displayed a net excess of one enantiomer (either the L- or the D-form) in 60 to 72% of these samples. These net enantiomeric excesses corresponded to compounds entirely biological but accounted for only about 5% of the total 2-methyltetrol mass in all the samples. Further analysis showed that, in addition, a large mass of the racemic fractions (equal mixtures of D- and L-forms) was also biological. Estimating the contribution of secondary reactions from the isomeric ratios measured in the samples (=ratios 2-methylthreitol over 2-methylerythritol), the mass fraction of secondary methyltetrols in these samples was estimated to a maximum of 31% and their primary fraction to a minimum of 69%. Such large primary fractions could have been expected in PM10 aerosols, largely influenced by biological emissions, and would now need to be investigated in finer aerosols. This work demonstrates the effectiveness of chiral and isomeric analyses as the first direct tool to assess the primary and secondary fractions of organic aerosols.
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| 2. |
- Karlsson, Nélida Jocelyn Donají, 1980-
(författare)
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Primary and secondary organics in biogenic atmospheric aerosol : The chiral study of 2-methyltetrols from method development to application
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Distinguishing between the primary and secondary origin of the organic components in atmospheric aerosols is one of the key parameters in assessing the relevance and role of different chemical species in the overall chemistry of the atmosphere. Currently available methods used in field measurements are not able to fully discriminate between the primary or secondary origin of compounds detected in atmospheric aerosols. This thesis presents a new analytical method for examining the primary and secondary origin of certain organic constituents, 2-methyltetrols, in biogenic atmospheric aerosol based on chirality. Chirality is a molecular structure property that makes a pair of compounds to be mirror images of each other. Consequently, compounds with chirality represent challenges for their study as individual species. This is of importance because 2-methyltetrols have been studied so far solely as two diastereomeric constituents, 2-methylerythritol and 2-methylthreitol, when in reality they are four different compounds: (2R,3S)-methylerythritol, (2S,3R)-methylerythritol, (2S,3S)-methylthreitol and (2R,3R)-mehtylthreitol. Furthermore, 2-methylerythritol and 2-methylthreitol are currently used as the main tracers for the contribution of isoprene to the formation of secondary organic aerosols in the atmosphere. Therefore, a new method directed to the chiral analysis of 2-methyltetrols was developed and applied to atmospheric samples collected at Aspvreten, Sweden, the Amazon, Brazil, and Hyytiälä, Finland. The results indicate that 2-methyltetrols in samples from the three sites have both primary and secondary origins with variability among sites as well as seasons. The estimates of the minimum primary origin contribution represent a significant fraction of the total mass of 2-methyltetrols in the samples. In some samples the contribution was as high as 30% of the total mass of these compounds. Even though 2-methyltetrols have secondary origin, their use as tracers for the atmospheric oxidation of isoprene should be discouraged, unless relative primary contributions are considered, as this study has demonstrated that they have primary origin as well. Moreover, the development and application of chiral analytical methods should be prioritized in order to improve the prevailing understanding of the real chemical composition and origin of chiral compounds in atmospheric aerosols.
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| 3. |
- Nobre, Carlos, et al.
(författare)
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ADDRESSING THE COMPLEXITY OF THE EARTH SYSTEM
- 2010
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 91:10, s. 1389-1396
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Rocha, Juan Carlos, 1984-
(författare)
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Regime Shifts in the Anthropocene
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Regime shifts are large, abrupt and often hard to reverse changes in the function and structure of socal-ecological systems. These regime shifts have been documented in a broad range of systems and scales both in marine, terrestrial and polar ecosystems. Regime shifts have attracted the attention of scientists, managers and policy makers because they substantially affect the flow of ecosystem services that society relies on. Despite their re|evance in the face of climate change or increasing pressure of the anthropocene, little is understood about the overall patterns of regime shifts causation and impacts for human well being. This licentiate thesis summarises the first steps towards a global assessment of regime shifts. Paper I is a literature review that attempts to synthesise the state of the art of regime shifts theory, its application in different disciplines, and frontiers of research. Paper II outlines a framework developed to study and compare regime shifts across different systems and scales, namely the Regime Shifts Database. Paper III investigates the patterns of drivers co-occurrence, and outlines the opportunities and challenges for management of regime shifts. The three papers together propose a new approach to study regime shifts that combines system thinking and tools from network science to analyze phenomena where knowledge about causal mechanisms, opportunities for experimentation and time series data are limited or unavailable. The discussion reflects upon the limitation and opportunities of our approach and outlines the guidelines for future developments of my PhD project.
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| 5. |
- Struthers, Hamish, et al.
(författare)
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Climate-induced changes in sea salt aerosol number emissions : 1870 to 2100
- 2013
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Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X. ; 118:2, s. 670-682
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Tidskriftsartikel (refereegranskat)abstract
- Global climate model output is combined with an emission parameterization to estimate the change in the global and regional sea salt aerosol number emission from 1870 to 2100. Global average results suggest a general increase in sea salt aerosol number emission due to increasing surface wind speed. However, the emission changes are not uniform over the aerosol size spectrum due to an increase in sea surface temperature. From 1870 to 2100 the emission of coarse mode particles (dry diameter D-P > 655 nm) increase by approximately 10 % (global average), whereas no significant change in the emission of ultrafine mode aerosols (dry diameter D-p < 76 nm) was found over the same period. Significant regional differences in the number emission trends were also found. Based on CAM-Oslo global climate model output, no straight-forward relationship was found between the change in the number emissions and changes in the sea salt aerosol burden or optical thickness. This is attributed to a change in the simulated residence time of the sea salt aerosol. For the 21st century, a decrease in the residence time leads to a weaker sea salt aerosol-climate feedback that what would be inferred based on changes in number emissions alone. Finally, quantifying any potential impact on marine stratocumulus cloud microphysical and radiative properties due to changes in sea salt aerosol number emissions is likely to be complicated by commensurate changes in anthropogenic aerosol emissions and changes in meteorology.
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| 6. |
- Zhao, R., et al.
(författare)
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Cloud partitioning of isocyanic acid (HNCO) and evidence of secondary source of HNCO in ambient air
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:19, s. 6962-6969
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Tidskriftsartikel (refereegranskat)abstract
- Although isocyanic acid (HNCO) may cause a variety of health issues via protein carbamylation and has been proposed as a key compound in smoke-related health issues, our understanding of the atmospheric sources and fate of this toxic compound is currently incomplete. To address these issues, a field study was conducted at Mount Soledad, La Jolla, CA, to investigate partitioning of HNCO to clouds and fogs using an Acetate Chemical Ionization Mass Spectrometer coupled to a ground-based counterflow virtual impactor. The first field evidence of cloud partitioning of HNCO is presented, demonstrating that HNCO is dissolved in cloudwater more efficiently than expected based on the effective Henry's law solubility. The measurements also indicate evidence for a secondary, photochemical source of HNCO in ambient air at this site.
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