Intense Arctic Ozone Depletion in the Spring of 2011

Observations of record-breaking ozone depletion during the Arctic spring of 2011 were made at 76˚ N in Thule, Greenland. The ozone total column amount of 290 DU measured on 18 March 2011 is the lowest value from the 12-year observation record and represents an ozone depletion of up to 48% of a typical March column. The unique 2010 – 11 vortex was characterized by sustained low stratospheric temperatures and stability that resisted breakup through March. Simultaneous observations of O3, HF, HCl, HNO3, and ClONO2 demonstrate strong subsidence and substantial conversion of chlorine from its normal reservoirs.Au printemps 2011, des observations d’appauvrissement record de l’ozone ont été faites dans l’Arctique à 76˚ N à Thule, au Groenland. Le 18 mars 2011, la colonne d’ozone total a été mesurée à 290 DU, ce qui représente la valeur la plus faible depuis que les observations ont commencé à être consignées il y a 12 ans. Cela constitue un appauvrissement de l’ozone allant jusqu’à 48 % de la colonne typiquement enregistrée en mars. Le vortex unique dénoté en 2010-2011 était caractérisé par des températures stratosphériques faibles et soutenues ainsi que par une stabilité ayant résisté à la dissipation jusqu’en mars. Des observations simultanées de O3, HF, HCl, HNO3 et ClONO2 ont démontré une forte subsidence et une conversion substan­tielle du chlore à partir des réservoirs normaux

Low-Cost Air Quality Monitoring Tools: From Research to Practice (A Workshop Summary).

In May 2017, a two-day workshop was held in Los Angeles (California, U.S.A.) to gather practitioners who work with low-cost sensors used to make air quality measurements. The community of practice included individuals from academia, industry, non-profit groups, community-based organizations, and regulatory agencies. The group gathered to share knowledge developed from a variety of pilot projects in hopes of advancing the collective knowledge about how best to use low-cost air quality sensors. Panel discussion topics included: (1) best practices for deployment and calibration of low-cost sensor systems, (2) data standardization efforts and database design, (3) advances in sensor calibration, data management, and data analysis and visualization, and (4) lessons learned from research/community partnerships to encourage purposeful use of sensors and create change/action. Panel discussions summarized knowledge advances and project successes while also highlighting the questions, unresolved issues, and technological limitations that still remain within the low-cost air quality sensor arena

Impact of Black Shale Weathering on Sediment Quality

Weathering of black shales leads to elevated metal concentrations in both surface water and stream sediments. In spite of the recent focus on black shales, few data exist on the ecological impacts of this process particularly on aquatic organisms. The key objective of this study was to determine the impact of trace metal concentrations in sediments upon aquatic organisms. To achieve the above objective, stream sediment samples were collected from streams draining black shale and limestone (used as a reference stream) lithologies located in central Arkansas between June 2003 and January 2004. Trace metal concentrations were measured by the dynamic reaction cell inductively coupled plasma mass spectrometry (ICPMS; Perkin Elmer DRC II) following EPA 6020 methodology. Sediment samples were tested for toxicity using standard EPA protocols. The trace metal concentrations in sediments and acute toxicity test findings using midge larvae, Chironomus tentans with endpoints measured as growth and survival is presented. Our results showed that there are significant differences in survival of the midge larvae among the study sites and also among the different sampling occasions. Percent survival of the midge larvae in the sediments derived from black shales was lower than that observed in the limestone-derived stream sediments. Significant differences in growth of the midge larvae were also observed among the sites with the control and reference stream sediments having higher growth than the black shale stream sediments. Though our measured metal concentrations in the black shale-derived sediments were below the Effects Range-Low, there is a great potential of metal accumulation in the fine sediment fraction particularly during baseflow regimes. At the time, metals can be concentrated in the fine sediment fraction due to the low discharge and less dilution. The study thus far has shown that the black shale metal-enriched stream sediments have both lethal and sublethal effects on aquatic organisms and higher organisms through food chain transfer

Shifting Perspectives: How Scrutiny Shapes the Relationship Between CEO Gender and Acquisition Activity

Research Summary: Several upper echelons studies have found that firms led by female executives are less likely to engage in risky endeavors than those led by male top executives. We argue that conceptualizing female CEOs as universally conservative decision-makers may paint too simplistic a picture and that the impact of CEO gender on strategic decision-making may vary significantly depending on the given situation CEOs are experiencing. We integrate executive job demands and gender research to propose that scrutiny will exhibit differential effects on female and male CEOs\u27 acquisition activity. We show that in high-scrutiny contexts, the difference between male and female CEO acquisition activity disappears. In contrast, in low-scrutiny contexts, the difference between male and female CEOs\u27 acquisition activity is exaggerated. Managerial Summary: Substantial research has shown that female executives acquire at a lower rate than male executives. We argue that viewing female CEOs as universally conservative decision-makers may paint too simplistic a picture and that the impact of CEO gender on strategic decision-making may vary significantly depending on the given situation CEOs are experiencing. In particular, we argue and find that in high-scrutiny contexts, the difference between male and female CEO acquisition activity disappears. This research suggests that managers should consider the impact of environmental context—especially the role of scrutiny—when considering the risk propensity of female leaders

Purification and Characterization of Glycogen Synthase from Ascaris Suum

Glycogen synthase, the enzyme that catalyzes the rate-limiting reaction of glycogen syntheses has been purified and characterized from Ascaris suum muscle. Glycogen in the crude extract was digested to release the enzyme, eluted from a DE52 cellulose column and then applied to a Sepharose affinity column. The purified Ascaris enzyme was found to be homologous to the mammalian enzyme with regard to subunit and holoenzyme Mr^3 allosteric activation, substrate affinity and covalent modification. However, the association between Ascaris glycogen synthase and endogenous glycogen differed from that in mammalian systems

Assessing positive matrix factorization model fit: a new method to estimate uncertainty and bias in factor contributions at the daily time scale

International audienceA Positive Matrix Factorization receptor model for aerosol pollution source apportionment was fit to a synthetic dataset simulating one year of daily measurements of ambient PM2.5 concentrations, comprised of 39 chemical species from nine pollutant sources. A novel method was developed to estimate model fit uncertainty and bias at the daily time scale, as related to factor contributions. A balanced bootstrap is used to create replicate datasets, with the same model then fit to the data. Neural networks are trained to classify factors based upon chemical profiles, as opposed to correlating contribution time series, and this classification is used to align factor orderings across results associated with the replicate datasets. Factor contribution uncertainty is assessed from the distribution of results associated with each factor. Comparing modeled factors with input factors used to create the synthetic data assesses bias. The results indicate that variability in factor contribution estimates does not necessarily encompass model error: contribution estimates can have small associated variability yet also be very biased. These results are likely dependent on characteristics of the data

Assessing positive matrix factorization model fit: a new method to estimate uncertainty and bias in factor contributions at the measurement time scale

A Positive Matrix Factorization receptor model for aerosol pollution source apportionment was fit to a synthetic dataset simulating one year of daily measurements of ambient PM<sub>2.5</sub> concentrations, comprised of 39 chemical species from nine pollutant sources. A novel method was developed to estimate model fit uncertainty and bias at the daily time scale, as related to factor contributions. A circular block bootstrap is used to create replicate datasets, with the same receptor model then fit to the data. Neural networks are trained to classify factors based upon chemical profiles, as opposed to correlating contribution time series, and this classification is used to align factor orderings across the model results associated with the replicate datasets. Factor contribution uncertainty is assessed from the distribution of results associated with each factor. Comparing modeled factors with input factors used to create the synthetic data assesses bias. The results indicate that variability in factor contribution estimates does not necessarily encompass model error: contribution estimates can have small associated variability across results yet also be very biased. These findings are likely dependent on characteristics of the data