A Case Study of Convectively Sourced Water Vapor Observed in the Overworld Stratosphere over the United States

On 27 August 2013, during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys field mission, NASA's ER2 research aircraft encountered a region of enhanced water vapor, extending over a depth of approximately 2 km and a minimum areal extent of 20,000 km(exp 2) in the stratosphere (375 K to 415 K potential temperature), south of the Great Lakes (42N, 90W). Water vapor mixing ratios in this plume, measured by the Harvard Water Vapor instrument, constitute the highest values recorded in situ at these potential temperatures and latitudes. An analysis of geostationary satellite imagery in combination with trajectory calculations links this water vapor enhancement to its source, a deep tropopausepenetrating convective storm system that developed over Minnesota 20 h prior to the aircraft plume encounter. High resolution, groundbased radar data reveal that this system was composed of multiple individual storms, each with convective turrets that extended to a maximum of ~4 km above the tropopause level for several hours. In situ water vapor data show that this storm system irreversibly delivered between 6.6 kt and 13.5 kt of water to the stratosphere. This constitutes a 2025% increase in water vapor abundance in a column extending from 115 hP to 70 hPa over the plume area. Both in situ and satellite climatologies show a high frequency of localized water vapor enhancements over the central U.S. in summer, suggesting that deep convection can contribute to the stratospheric water budget over this region and season

Impact of recent laboratory measurements of the absorption cross section of ClOOCl on our understanding of polar ozone chemistry: Part II, Modeled and Measured ClOx during SOLVE

The photolysis of ClOOCl limits loss of polar ozone by the ClO+ClO cycle. New laboratory measurements of the ClOOCl cross section suggest that its photolysis is about a factor of six slower than a value based on current recommendations. We show the incorporation of these new cross sections into a photochemical model leads to poor agreement with values of ClO and ClOOCl measured during the SOLVE campaign, with the model under-estimating measured ClO and over-estimating measured ClOOCl by amounts that are much larger than the measurement uncertainties. These comparisons indicate that a model using the new cross section, and no other changes, provides a poor description of the partitioning of ClO and ClOOCl. Such a simulation also results in much slower ozone loss rates compared to a model using standard chemistry. It should be noted that, in the absence of the new cross section, there is still inconsistencies in our understanding of stratospheric chlorine when compared to stratospheric observations. We use the SOLVE data set to test a variety of postulated processes, discussed in a companion presentation, that could be invoked to resolve these discrepancies. The SOLVE data set is noteworthy because it provides a comprehensive description of the diurnal variation ClO and ClOOCl partitioning. For example, sufficient data was obtained during morning and evening to test hypothesis that result in predicted diurnal asymmetries in the partitioning. Implications of proposed new chemical mechanisms for ozone loss rates will also be discussed

Correlates of Physical Activity, Psychosocial Factors, and Home Environment Exposure among U.S. Adolescents: Insights for Cancer Risk Reduction from the FLASHE Study

Background and aims: Physical activity (PA) can bring numerous health benefits to adolescents and can largely aid in reducing the various types of cancer risks in their lifespans. However, few adolescents meet the physical activity guidelines recommended by the National Cancer Institute in the United States. Our study aimed to examine the multilevel determinants potentially influencing adolescent’s PA participation. Methods: A secondary analysis of physical activity, home and school neighborhood, and other psychosocial data from 1504 dyads of adolescents and their parents who participated in the 2014 Family Life, Activity, Sun, Health, and Eating (FLASHE) study was performed. Analysis of variance and general linear model analyses were used to examine the correlates. Results: General linear modeling revealed that younger adolescents participated in greater levels of PA than older adolescents (p < 0.001). Adolescents whose parents reported meeting PA guidelines participated in greater amounts of PA (p < 0.001). Parental support of adolescent PA (p < 0.001) was also predictive of adolescent PA levels. Furthermore, parents who reported meeting moderate-to-vigorous physical activity (MVPA) guidelines were more likely to have teenagers that engaged in higher amounts of PA (p < 0.001). Discussion and Conclusions: Our findings imply a dynamic relationship between adolescent and parent MVPA levels. Interventions focused on increasing parental MVPA and encouraging parents to engage in promoting PA are merited in order to aid in increasing PA among adolescents while reducing the cancer risk

'pH-jump' crystallographic analyses of gamma-lactam-porcine pancreatic elastase complexes.

beta-Lactams inhibit a range of enzymes via acylation of nucleophilic serine residues. Certain gamma-lactam analogues of monocyclic beta-lactams have also been shown to be reversible inhibitors of porcine pancreatic elastase (PPE), forming acyl-enzyme complexes that are stable with respect to hydrolysis. Crystallographic analysis at pH 5 of an acyl-enzyme complex formed with PPE and one of these inhibitors revealed the ester carbonyl located in the oxyanion hole in a similar conformation to that observed in the structure of a complex formed between a heptapeptide (beta-casomorphin-7) and PPE. Only weak electron density was observed for the His-57 side chain in its 'native' conformation. Instead, the His-57 side chain predominantly adopted a conformation rotated approx. 90 degrees from its normal position. PPE-gamma-lactam crystals were subjected to 'pH-jumps' by placing the crystals in a buffer of increased pH prior to freezing for data collection. The results indicate that the conformation of the gamma-lactam-derived acyl-enzyme species in the PPE active site is dependent on pH, a result having implications for the analysis of other serine protease-inhibitor structures at non-catalytic pH values. The results help to define the stereoelectronic relationship between the ester of the acyl-enzyme complex, the side chain of His-57 and the incoming nucleophile during the reversible (de)acylation steps, implying it is closely analogous to the hydrolytic deacylation step during catalytic peptide hydrolysis

X-ray structure of a serine protease acyl-enzyme complex at 0.95-A resolution.

Kinetic analyses led to the discovery that N-acetylated tripeptides with polar residues at P3 are inhibitors of porcine pancreatic elastase (PPE) that form unusually stable acyl-enzyme complexes. Peptides terminating in a C-terminal carboxylate were more potent than those terminating in a C-terminal amide, suggesting recognition by the oxy-anion hole is important in binding. X-ray diffraction data were recorded to 0.95-A resolution for an acyl-enzyme complex formed between PPE and N-acetyl-Asn-Pro-Ile-CO2H at approximately pH 5. The accuracy of the crystallographic coordinates allows structural issues concerning the mechanism of serine proteases to be addressed. Significantly, the ester bond of the acyl-enzyme showed a high level of planarity, suggesting geometric strain of the ester link is not important during catalysis. Several hydrogen atoms could be clearly identified and were included within the model. In keeping with a recent x-ray structure of subtilisin at 0.78 A (1), limited electron density is visible consistent with the putative location of a hydrogen atom approximately equidistant between the histidine and aspartate residues of the catalytic triad. Comparison of this high resolution crystal structure of the acyl-enzyme complex with that of native elastase at 1.1 A (2) showed that binding of the N-terminal part of the substrate can be accommodated with negligible structural rearrangements. In contrast, comparison with structures obtained as part of "time-resolved" studies on the reacting acyl-enzyme complex at >pH 7 (3) indicate small but significant structural differences, consistent with the proposed synchronization of ester hydrolysis and substrate release