8,945 research outputs found
Yields of oxidized volatile organic compounds during the OH radical initiated oxidation of isoprene, methyl vinyl ketone, and methacrolein under high-NO_x conditions
We present first-generation and total production yields of glyoxal, methylglyoxal, glycolaldehyde, and hydroxyacetone from the oxidation of isoprene, methyl vinyl ketone (MVK), and methacrolein (MACR) with OH under high NO_x conditions. Several of these first-generation yields are not included in commonly used chemical mechanisms, such as the Leeds Master Chemical Mechanism (MCM) v. 3.2. The first-generation yield of glyoxal from isoprene was determined to be 2.1 (±0.6)%. Inclusion of first-generation production of glyoxal, glycolaldehyde and hydroxyacetone from isoprene greatly improves performance of an MCM based model during the initial part of the experiments. In order to further improve performance of the MCM based model, higher generation glyoxal production was reduced by lowering the first-generation yield of glyoxal from C5 hydroxycarbonyls. The results suggest that glyoxal production from reaction of OH with isoprene under high NO_x conditions can be approximated by inclusion of a first-generation production term together with secondary production only via glycolaldehyde. Analogously, methylglyoxal production can be approximated by a first-generation production term from isoprene, and secondary production via MVK, MACR and hydroxyacetone. The first-generation yields reported here correspond to less than 5% of the total oxidized yield from isoprene and thus only have a small effect on the fate of isoprene. However, due to the abundance of isoprene, the combination of first-generation yields and reduced higher generation production of glyoxal from C5 hydroxycarbonyls is important for models that include the production of the small organic molecules from isoprene
Birational Geometry of Singular Moduli Spaces of O'Grady Type
Following Bayer and Macr\`{i}, we study the birational geometry of singular
moduli spaces of sheaves on a K3 surface which admit symplectic
resolutions. More precisely, we use the Bayer-Macr\`{i} map from the space of
Bridgeland stability conditions to the cone of movable
divisors on to relate wall-crossing in to birational
transformations of . We give a complete classification of walls in
and show that every birational model of obtained by
performing a finite sequence of flops from appears as a moduli space of
Bridgeland semistable objects on . An essential ingredient of our proof is
an isometry between the orthogonal complement of a Mukai vector inside the
algebraic Mukai lattice of and the N\'{e}ron-Severi lattice of which
generalises results of Yoshioka, as well as Perego and Rapagnetta. Moreover,
this allows us to conclude that the symplectic resolution of is deformation
equivalent to the 10-dimensional irreducible holomorphic symplectic manifold
found by O'Grady.Comment: Final versio
Reactive intermediates revealed in secondary organic aerosol formation from isoprene
Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = β-IEPOX + δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NO_x conditions, respectively. Isoprene low-NO_x SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO_x conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO_x SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO_2 and NO_2, respectively) could be a substantial source of “missing urban SOA” not included in current atmospheric models
Surface and boundary layer exchanges of volatile organic compounds, nitrogen oxides and ozone during the GABRIEL campaign
We present an evaluation of sources, sinks and turbulent transport of nitrogen oxides, ozone and volatile organic compounds (VOC) in the boundary layer over French Guyana and Suriname during the October 2005 GABRIEL campaign by simulating observations with a single-column chemistry and climate model (SCM) along a zonal transect. Simulated concentrations of O3 and NO as well as NO2 photolysis rates over the forest agree well with observations when a small soil-biogenic NO emission flux was applied. This suggests that the photochemical conditions observed during GABRIEL reflect a pristine tropical low-NOx regime. The SCM uses a compensation point approach to simulate nocturnal deposition and daytime emissions of acetone and methanol and produces daytime boundary layer mixing ratios in reasonable agreement with observations. The area average isoprene emission flux, inferred from the observed isoprene mixing ratios and boundary layer height, is about half the flux simulated with commonly applied emission algorithms. The SCM nevertheless simulates too high isoprene mixing ratios, whereas hydroxyl concentrations are strongly underestimated compared to observations, which can at least partly explain the discrepancy. Furthermore, the model substantially overestimates the isoprene oxidation products methlyl vinyl ketone (MVK) and methacrolein (MACR) partly due to a simulated nocturnal increase due to isoprene oxidation. This increase is most prominent in the residual layer whereas in the nocturnal inversion layer we simulate a decrease in MVK and MACR mixing ratios, assuming efficient removal of MVK and MACR. Entrainment of residual layer air masses, which are enhanced in MVK and MACR and other isoprene oxidation products, into the growing boundary layer poses an additional sink for OH which is thus not available for isoprene oxidation. Based on these findings, we suggest pursuing measurements of the tropical residual layer chemistry with a focus on the nocturnal depletion of isoprene and its oxidation products
The concentration of oleocanthal in olive oil waste
The aim of this study was to determine the concentration of oleocanthal in olive pomace waste and compare this to its concentration in extra-virgin olive oil (EVOO). The concentration of oleocanthal in freshly pressed EVOO and its subsequent waste was analysed at early, mid and late season harvests. Oleocanthal concentrations were quantified using high-performance liquid chromatography–mass spectrometry. In oil, oleocanthal concentration was as follows: 123.24 ± 6.48 mg kg¯¹1 in early harvest, 114.20 ± 17.42 mg kg¯¹ in mid harvest and 152.22 ± 10.54 mg kg¯¹ in late harvest. Its concentration in waste was determined to be: 128.25 ± 11.33 mg kg¯¹ in early harvest, 112.15 ± 1.51mg kg¯¹ in mid harvest and 62.35 ± 8.00 mg kg¯¹ in late harvest. Overall, olive pomace waste is a valuable source of oleocanthal.<br /
Extremal rays and automorphisms of holomorphic symplectic varieties
We survey recent results on ample cones and birational contractions of
holomorphic symplectic varieties of K3 type, focusing on explicit constructions
and concrete examples.Comment: 24 page
Bridgeland Stability conditions on threefolds I: Bogomolov-Gieseker type inequalities
We construct new t-structures on the derived category of coherent sheaves on
smooth projective threefolds. We conjecture that they give Bridgeland stability
conditions near the large volume limit. We show that this conjecture is
equivalent to a Bogomolov-Gieseker type inequality for the third Chern
character of certain stable complexes. We also conjecture a stronger
inequality, and prove it in the case of projective space, and for various
examples.
Finally, we prove a version of the classical Bogomolov-Gieseker inequality,
not involving the third Chern character, for stable complexes.Comment: 45 pages, 4 figures. Comments are welcome. v2: Referee comments
incorporated. To appear in JA
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