Biological Degradation of Acetaldehyde in Southern California Coastal Waters

Oxygenated hydrocarbons are ubiquitous in the atmosphere with levels ranging from low ppt (acetaldehyde) to low ppb (methanol). As an OH sink and an atmospheric HOx and ozone source, oxygenated hydrocarbons have a direct impact on the oxidative capacity of the atmosphere. The oceans are one of the largest sources of uncertainty in current atmospheric budget estimates of these species. A better understanding of the processes that produce and destroy these species in seawater would improve our understanding of the role of the oceans in cycling these species into or out of the atmosphere. We have measured the degradation rate of acetaldehyde in unfiltered and filtered southern California coastal waters. Rates were determined by following the concentrations of D-4 labelled acetaldehyde in spiked (nM levels) seawater in 100ml glass syringes as a function of time. Concentrations were determined by isotope dilution purge and trap gas chromatography mass spectrometry using C-13 labelled acetaldehyde as the internal standard. Degradation rates in 0.2um filtered seawater were not measurable. Degradation rates in unfiltered seawater were first order and ranged from 0.046 to 0.32 hr-1. Bacteria levels were also measured in all samples. Acetaldehyde degradation rates scale with bacteria levels. Variability as a function of time, rainfall and other water quality parameters will be discussed

The Degradation of Acetaldehyde in Estuary Waters in Southern California, USA

Acetaldehyde plays an important role in oxidative cycles in the troposphere. Estimates of its air-water flux are important in global models. Biological degradation is believed to be the dominant loss process in water, but there have been few measurements, none in estuaries. Acetaldehyde degradation rates were measured in surface waters at the inflow to the Upper Newport Back Bay estuary in Orange County, Southern California, USA, over a 6-month period including the rainy winter season. Deuterated acetaldehyde was added to filtered and unfiltered water samples incubated in glass syringes, and its loss analyzed by purge and trap gas chromatography mass spectrometry. Filtered samples showed no significant degradation, suggesting that particle-mediated degradation is the dominant removal process. Correlation between measured degradation rate constants in unfiltered incubations and bacteria counts suggests the loss is due to microorganisms. Degradation in unfiltered samples followed first-order kinetics, with rate constants ranging from 0.0006 to 0.025 min-1 (k; average 0.0043 ± 0.006 min-1). Turnover (1/k) ranged from 40 to 1667 min, consistent with prior studies in coastal waters. Acetaldehyde concentrations in the estuary are estimated to range from 30 to ~500 nM (average ~250 nM). Results suggest the estuary is a source of acetaldehyde to the atmosphere

Ultrafast X-ray Diffraction Study of a Shock-Compressed Iron Meteorite above 100 GPa

Natural kamacite samples (Fe92.5Ni7.5) from a fragment of the Gibeon meteorite were studied as a proxy material for terrestrial cores to examine phase transition kinetics under shock compression for a range of different pressures up to 140 GPa. In situ time-resolved X-ray diffraction (XRD) data were collected of a body-centered cubic (bcc) kamacite section that transforms to the high-pressure hexagonal close-packed (hcp) phase with sub-nanosecond temporal resolution. The coarse-grained crystal of kamacite rapidly transformed to highly oriented crystallites of the hcp phase at maximum compression. The hcp phase persisted for as long as 9.5 ns following shock release. Comparing the c/a ratio with previous static and dynamic work on Fe and Fe-rich Fe-Ni alloys, it was found that some shots exhibit a larger than ideal c/a ratio, up to nearly 1.65. This work represents the first time-resolved laser shock compression structural study of a natural iron meteorite, relevant for understanding the dynamic material properties of metallic planetary bodies during impact events and Earth’s core elasticity

Behavior of soda-lime silicate glass under laser-driven shock compression up to 315 GPa

Shock experiments give a unique insight into the behavior of matter subjected to extremely high pressures and temperatures. Understanding the behavior of materials under such extreme conditions is key to modeling material failure and deformation dynamics under impact. While studies on pure silica are extensive, the shock behavior of other commercial silicates that contain additional oxides has not been systematically investigated. To better understand the role of composition in the dynamic behavior of silicates, we performed laser-driven dynamic compression experiments on soda-lime glass (SLG) up to 315 GPa. Using the accurate pulse shaping offered by the long pulse laser system at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLG was shock compressed along the Hugoniot to multiple pressure-temperature points. Velocity Interferometer System for Any Reflector was used to measure the velocity and determine the pressure inside the SLG. The U s -u p relationship obtained agrees well with the previous parallel plate impact studies. Within the error bars, no transformation to the crystalline phase was observed up to 70 GPa, which is in contrast to the behavior of pure silica under shock compression. Our studies show that the glass composition strongly influences the shock compression behavior of the silicate glasses