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| 2. |
- Mehra, A., et al.
(författare)
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The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and Raman microscopy
- 2021
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Ingår i: Faraday Discussions. - 1359-6640. ; 226, s. 382-408
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Tidskriftsartikel (refereegranskat)abstract
- Cooking emissions account for a significant proportion of the organic aerosols emitted into the urban environment and high pollution events have been linked to an increased organic content on urban particulate matter surfaces. We present a kinetic study on surface coatings of self-assembled (semi-solid) oleic acid-sodium oleate cooking aerosol proxies undergoing ozonolysis. We found clear film thickness-dependent kinetic behaviour and measured the effect of the organic phase on the kinetics for this system. In addition to the thickness-dependent kinetics, we show that significant fractions of unreacted proxy remain after extensive ozone exposure and that this effect scales approximately linearly with film thickness, suggesting that a late-stage inert reaction product may form and inhibit reaction progress - effectively building up an inert crust. We determine this by using a range of simultaneous analytical techniques; most notably Small-Angle X-ray Scattering (SAXS) has been used for the first time to measure the reaction kinetics of films of a wide range of thicknesses from ca. 0.59 to 73 mu m with films <10 mu m thick being of potential atmospheric relevance. These observations have implications for the evolution of particulate matter in the urban environment, potentially extending the atmospheric lifetimes of harmful aerosol components and affecting the local urban air quality and climate.
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| 3. |
- Mehra, A., et al.
(författare)
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Using highly time-resolved online mass spectrometry to examine biogenic and anthropogenic contributions to organic aerosol in Beijing
- 2021
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Ingår i: Faraday Discussions. - 1359-6640. ; 226, s. 382-408
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Tidskriftsartikel (refereegranskat)abstract
- Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C-5-C-9 and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, alpha -pinene and sesquiterpenes.
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| 4. |
- Ouyang, D. L., et al.
(författare)
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Influence of casting temperature on the castability and glass-forming ability of Zr-based bulk metallic glasses
- 2023
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093. ; 603
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Tidskriftsartikel (refereegranskat)abstract
- Both castability and glass-forming ability (GFA) are crucial for die-casting of Zr-based bulk metallic glass (BMG) components. In this work, a simple method is used to quantify the castability required for casting two SIM card slots with different designs, and to quantify the castability at different casting temperatures. It is found that the Zr55Cu30Ni5Al10 (Zr55) BMG has a wider optimal casting temperature region (in which glassy rods with a diameter of at least 5 mm can be formed) than that of Zr52.5Cu25Ni9.5Al7Ti6 (Zr52.5), which is consistent of the better GFA of the Zr55. In the optimal casting temperature region, however, the castability of Zr52.5 is significantly better than that of Zr55, because Zr52.5 has a lower melting point, a poorer wettability to the copper mold, and a higher optimal casting temperature. These results are helpful to guide the production of Zr-based BMG components.
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| 5. |
- Qi, D., et al.
(författare)
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Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:4
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Tidskriftsartikel (refereegranskat)abstract
- The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 17-year (2002-2019) observational data set in the Chukchi Sea to determine the long-term changes in pH and aragonite saturation state (omega(arag)). We found that pH and omega(arag) declined in different water masses with average rates of -0.0047 +/- 0.0026 years(-1) and -0.017 +/- 0.009 years(-1), respectively, and are similar to 2-3 times faster than those solely due to increasing atmospheric CO2. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt-induced increased atmospheric CO2 invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient-rich Pacific water.
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