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Margaret A Tolbert - One of the best experts on this subject based on the ideXlab platform.
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state transformations and ice nucleation in amorphous semi solid Organic aerosol
Atmospheric Chemistry and Physics, 2013Co-Authors: K J Baustian, Matthew E Wise, E J Jensen, Gregory P Schill, Miriam Arak Freedman, Margaret A TolbertAbstract:Abstract. Amorphous (semi-)solid Organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy have been used in conjunction with a cold stage to examine water uptake and ice nucleation on individual amorphous (semi-)solid particles at atmospherically relevant temperatures (200–273 K). Three Organic compounds considered proxies for atmospheric secondary Organic aerosol (SOA) were used in this investigation: sucrose, citric acid and glucose. Internally mixed particles consisting of each Organic and ammonium Sulfate were also investigated. Results from water uptake experiments followed the shape of a humidity-induced glass transition (Tg(RH)) curve and were used to construct state diagrams for each Organic and corresponding mixture. Experimentally derived Tg(RH) curves are in good agreement with theoretical predictions of Tg(RH) following the approach of Koop et al. (2011). A unique humidity-induced glass transition point on each state diagram, Tg'(RH), was used to quantify and compare results from this study to previous works. Values of Tg'(RH) determined for sucrose, glucose and citric acid glasses were 236, 230 and 220 K, respectively. Values of Tg'(RH) for internally mixed Organic/Sulfate particles were always significantly lower; 210, 207 and 215 K for sucrose/Sulfate, glucose/Sulfate and citric acid/Sulfate, respectively. All investigated SOA proxies were observed to act as heterogeneous ice nuclei at tropospheric temperatures. Heterogeneous ice nucleation on pure Organic particles occurred at Sice = 1.1–1.4 for temperatures below 235 K. Particles consisting of 1:1 Organic-Sulfate mixtures took up water over a greater range of conditions but were in some cases also observed to heterogeneously nucleate ice at temperatures below 202 K (Sice= 1.25–1.38). Polynomial curves were fitted to experimental water uptake data and then incorporated into the Community Aerosol Radiation Model for Atmospheres (CARMA) along with the predicted range of humidity-induced glass transition temperatures for atmospheric SOA from Koop et al. (2011). Model results suggest that Organic and Organic/Sulfate aerosol could be glassy more than 60% of the time in the midlatitude upper troposphere and more than 40% of the time in the tropical tropopause region (TTL). At conditions favorable for ice formation (Sice > 1), particles in the TTL are expected to be glassy more than 50% of the time for temperatures below 200 K. Results from this study suggests that amorphous (semi-)solid Organic particles are often present in the upper troposphere and that heterogeneous ice formation on this type of particle may play an important role in cirrus cloud formation.
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heterogeneous ice nucleation on phase separated Organic Sulfate particles effect of liquid vs glassy coatings
Atmospheric Chemistry and Physics, 2012Co-Authors: Margaret A Tolbert, G P SchillAbstract:Abstract. Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both Sulfates and Organics. The hygroscopic phase transitions of Organic-Sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, Organic-Sulfate particles are known to undergo another phase transition known as liquid–liquid phase separation. The ice nucleation properties of particles that have undergone liquid–liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid–liquid phase separation behavior of 2 : 1 mixtures of Organic polyols (1,2,6-hexanetriol and 1 : 1 1,2,6-hexanetriol + 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol) and ammonium Sulfate from 240–265 K. Further, the ice nucleation efficiency of these Organic-Sulfate systems after liquid–liquid phase separation and efflorescence was investigated from 210–235 K. Raman mapping and volume-geometry analysis indicate that these particles contain solid ammonium Sulfate cores fully engulfed in Organic shells. For the ice nucleation experiments, we find that if the Organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium Sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium Sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the Organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase-separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium Sulfate.
S M King - One of the best experts on this subject based on the ideXlab platform.
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cloud droplet activation of mixed Organic Sulfate particles produced by the photooxidation of isoprene
Atmospheric Chemistry and Physics, 2010Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Zhe Wang, G BiskosAbstract:The cloud condensation nuclei (CCN) properties of ammonium Sulfate particles mixed with Organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for Organic particle mass concentrations of 0.5 to 10.0 ?g m?3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Kohler model having two internally mixed components, namely ammonium Sulfate and secondary Organic material. The modeled physicochemical parameters of the Organic material were equivalent to an effective hygroscopicity parameter ?ORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual Organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary Organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for ?ORG is representative of both anthropogenic and biogenic secondary Organic material. This finding supports the use of ?ORG as a simplified yet accurate general parameter to represent the CCN activation of secondary Organic material in large-scale atmospheric and climate models.
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cloud condensation nucleus activity of secondary Organic aerosol particles mixed with Sulfate
Geophysical Research Letters, 2007Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Scot T MartinAbstract:from 23 to 37 m gm � 3 . CCN analysis was performed for 80to 150-nm particles having variable Organic-Sulfate volume fractions, which were estimated from the diameter of the Organic-Sulfate particle relative to that of the seed as well as independently from mass spectra. Critical supersaturation, which increased for greater SOA volume fraction and �� ;
Bert Van Loo - One of the best experts on this subject based on the ideXlab platform.
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structural and mechanistic analysis of the choline sulfatase from sinorhizobium melliloti a class i sulfatase specific for an alkyl Sulfate ester
Journal of Molecular Biology, 2018Co-Authors: Bert Van Loo, Markus Schober, Eugene Valkov, Magdalena Heberlein, Erich Bornbergbauer, Kurt Faber, M Hyvonen, Florian HollfelderAbstract:Abstract Hydrolysis of Organic Sulfate esters proceeds by two distinct mechanisms, water attacking at either sulfur (S–O bond cleavage) or carbon (C–O bond cleavage). In primary and secondary alkyl Sulfates, attack at carbon is favored, whereas in aromatic Sulfates and Sulfated sugars, attack at sulfur is preferred. This mechanistic distinction is mirrored in the classification of enzymes that catalyze Sulfate ester hydrolysis: arylsulfatases (ASs) catalyze S–O cleavage in Sulfate sugars and arylSulfates, and alkyl sulfatases break the C–O bond of alkyl Sulfates. Sinorhizobium meliloti choline sulfatase (SmCS) efficiently catalyzes the hydrolysis of alkyl Sulfate choline-O-Sulfate (kcat/KM = 4.8 × 103 s− 1 M− 1) as well as arylSulfate 4-nitrophenyl Sulfate (kcat/KM = 12 s− 1 M− 1). Its 2.8-A resolution X-ray structure shows a buried, largely hydrophobic active site in which a conserved glutamate (Glu386) plays a role in recognition of the quaternary ammonium group of the choline substrate. SmCS structurally resembles members of the alkaline phosphatase superfamily, being most closely related to dimeric ASs and tetrameric phosphonate monoester hydrolases. Although > 70% of the amino acids between protomers align structurally (RMSDs 1.79–1.99 A), the oligomeric structures show distinctly different packing and protomer–protomer interfaces. The latter also play an important role in active site formation. Mutagenesis of the conserved active site residues typical for ASs, H218O-labeling studies and the observation of catalytically promiscuous behavior toward phosphoesters confirm the close relation to alkaline phosphatase superfamily members and suggest that SmCS is an AS that catalyzes S–O cleavage in alkyl Sulfate esters with extreme catalytic proficiency.
John E Shilling - One of the best experts on this subject based on the ideXlab platform.
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cloud droplet activation of mixed Organic Sulfate particles produced by the photooxidation of isoprene
Atmospheric Chemistry and Physics, 2010Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Zhe Wang, G BiskosAbstract:The cloud condensation nuclei (CCN) properties of ammonium Sulfate particles mixed with Organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for Organic particle mass concentrations of 0.5 to 10.0 ?g m?3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Kohler model having two internally mixed components, namely ammonium Sulfate and secondary Organic material. The modeled physicochemical parameters of the Organic material were equivalent to an effective hygroscopicity parameter ?ORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual Organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary Organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for ?ORG is representative of both anthropogenic and biogenic secondary Organic material. This finding supports the use of ?ORG as a simplified yet accurate general parameter to represent the CCN activation of secondary Organic material in large-scale atmospheric and climate models.
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cloud condensation nucleus activity of secondary Organic aerosol particles mixed with Sulfate
Geophysical Research Letters, 2007Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Scot T MartinAbstract:from 23 to 37 m gm � 3 . CCN analysis was performed for 80to 150-nm particles having variable Organic-Sulfate volume fractions, which were estimated from the diameter of the Organic-Sulfate particle relative to that of the seed as well as independently from mass spectra. Critical supersaturation, which increased for greater SOA volume fraction and �� ;
Thomas Rosenoern - One of the best experts on this subject based on the ideXlab platform.
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cloud droplet activation of mixed Organic Sulfate particles produced by the photooxidation of isoprene
Atmospheric Chemistry and Physics, 2010Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Zhe Wang, G BiskosAbstract:The cloud condensation nuclei (CCN) properties of ammonium Sulfate particles mixed with Organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for Organic particle mass concentrations of 0.5 to 10.0 ?g m?3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Kohler model having two internally mixed components, namely ammonium Sulfate and secondary Organic material. The modeled physicochemical parameters of the Organic material were equivalent to an effective hygroscopicity parameter ?ORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual Organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary Organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for ?ORG is representative of both anthropogenic and biogenic secondary Organic material. This finding supports the use of ?ORG as a simplified yet accurate general parameter to represent the CCN activation of secondary Organic material in large-scale atmospheric and climate models.
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cloud condensation nucleus activity of secondary Organic aerosol particles mixed with Sulfate
Geophysical Research Letters, 2007Co-Authors: S M King, Thomas Rosenoern, John E Shilling, Qi Chen, Scot T MartinAbstract:from 23 to 37 m gm � 3 . CCN analysis was performed for 80to 150-nm particles having variable Organic-Sulfate volume fractions, which were estimated from the diameter of the Organic-Sulfate particle relative to that of the seed as well as independently from mass spectra. Critical supersaturation, which increased for greater SOA volume fraction and �� ;