While deformation at the Earth's surface primarily occurs along tectonic plate boundaries, major earthquakes have shaken regions deep within continental interiors. Three of the largest (M > 7.5) ...historic intraplate earthquakes occurred within the Indian subcontinent, suggesting the possibility of significant intraplate deformation. We consider surface velocities determined from new GPS data collected at 29 continuous GPS stations and 41 survey‐mode GPS stations in India between 1995 and 2007 to find a north‐south shortening rate of 0.3 ± 0.05 nanostrain yr−1, which may be accommodated by 2 ± 1 mm/yr of more localized convergence across central India. Southward motions at 4–7 mm/yr of sites on the Shillong plateau in northeast India reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau. The width and magnitude of the elastic strain accumulation field across the Himalaya varies little from ∼76°–90° longitude, but the strain is more broadly distributed and convergence rates are higher along the eastern ∼200 km of the range.
The hydroxyl radical (OH) is the most important oxidant in the atmosphere and the primary sink for isoprene, the dominant volatile organic compound emitted by vegetation. Recent research on the ...atmospheric oxidation capacity in isoprene‐dominated environments has suggested missing radical sources leading to significant overestimation of the lifetime of isoprene. Here we report, for the first time, a comprehensive experimental budget of isoprene in the planetary boundary layer based on airborne flux measurements along with in situ OH observations in the Southeast and Central U.S. Our findings show that surface heterogeneity of isoprene emissions lead to a physical separation of isoprene and OH resulting in an effective slowdown in the chemistry. Depending on surface heterogeneity, the intensity of segregation (Is) could locally slow down isoprene chemistry up to 30%. The effect of segregated reactants in the planetary boundary layer on average has an influence on modeled OH radicals that is comparable to that of recently proposed radical recycling mechanisms.
Key Points
Slowdown in isoprene chemistry due to chemistry‐turbulence interactions
Smaller differences between modeled and observed OH densities than in previous studies
As part of the Deep Convective Cloud and Chemistry (DC3) experiment, the National Science Foundation/National Center for Atmospheric Research (NCAR) Gulfstream‐V (GV) and NASA DC‐8 research aircraft ...probed the chemical composition of the inflow and outflow of two convective storms (north storm, NS, south storm, SS) originating in the Colorado region on 22 June 2012, a time when the High Park wildfire was active in the area. A wide range of trace species were measured on board both aircraft including biomass burning (BB) tracers hydrogen cyanide (HCN) and acetonitrile (ACN). Acrolein, a much shorter lived tracer for BB, was also quantified on the GV. The data demonstrated that the NS had ingested fresh smoke from the High Park fire and as a consequence had a higher VOC OH reactivity than the SS. The SS lofted aged fire tracers along with other boundary layer ozone precursors and was more impacted by lightning NOx (LNOx) than the NS. The NCAR master mechanism box model was initialized with measurements made in the outflow of the two storms. The NS and SS were predicted to produce 11 and 14 ppbv of O3, respectively, downwind of the storm over 2 days. Sensitivity tests revealed that the ozone production potential of the SS was highly dependent on LNOx. Normalized excess mixing ratios, ΔX/ΔCO, for HCN and ACN were determined in both the fire plume and the storm outflow and found to be 7.0 ± 0.5 and 2.3 ± 0.5 pptv ppbv−1, respectively, and 1.4 ± 0.3 pptv ppbv−1 for acrolein in the outflow only.
Key Points
Lightning NOx is a key driver of ozone production in storm outflows
Storms can transport biomass burning emissions to the upper troposphere
Acrolein is shown to be a good tracer for fresh biomass burning emissions
The objective of the study was to analyze the nucleation, primary phase formation and solid state reaction to form lithium disilicate glass–ceramics derived from the SiO
2–Li
2O–Al
2O
3–K
2O–ZrO
2–P
...2O
5 system. The concentration of P
2O
5 was increased from zero up to 3.2
wt%. Thermal analysis, scanning electron microscopy and X-ray diffraction were used to characterize the microstructure formation, the nucleation process and the solid state reaction of the crystal phase precipitation in the glass–ceramics. Additives of P
2O
5 allowed the control of bulk crystallization. Nucleation was catalyzed by nano-scaled Li
3PO
4 phases, visualized by HR-SEM. Li
3PO
4 reacts most probably as the heterogeneous catalyst, acting by epitaxy, of both Li
2SiO
3 and Li
2Si
2O
5 crystals. Based on the discussion of the main results, the authors deduced a four-step reaction mechanism. This mechanism demonstrated that after nucleation of lithium metasilicate and lithium disilicate, the latter phase grows as agglomerated nanocrystals, but remained in a relative small amount. By contrast, lithium metasilicate grows rapidly and decomposes at 780–820
°C with the result of a drastic increase of lithium disilicate phase. This was a result of a solid state reaction with the SiO
2-rich glassy phase. In a parallel reaction, cristobalite was formed as a preliminary phase. The final product of a glass–ceramic with 3.2
wt% P
2O
5 shows a highly crystalline interlocking microstructure demonstrating a high-strength of 726
±
63
MPa and translucency.
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