Evidence for renoxification in the tropical marine boundary layer

We present 2 years of NOx observations from the Cape Verde Atmospheric Observatory located in the tropical Atlantic boundary layer. We find that NOx mixing ratios peak around solar noon (at 20-30pptV depending on season), which is counter to box model simulations that show a midday minimum due to OH conversion of NO2 to HNO3. Production of NOx via decomposition of organic nitrogen species and the photolysis of HNO3 appear insufficient to provide the observed noontime maximum. A rapid photolysis of nitrate aerosol to produce HONO and NO2, however, is able to simulate the observed diurnal cycle. This would make it the dominant source of NOx at this remote marine boundary layer site, overturning the previous paradigm according to which the transport of organic nitrogen species, such as PAN, is the dominant source. We show that observed mixing ratios (November-December 2015) of HONO at Cape Verde (∼ 3.5pptV peak at solar noon) are consistent with this route for NOx production. Reactions between the nitrate radical and halogen hydroxides which have been postulated in the literature appear to improve the box model simulation of NOx. This rapid conversion of aerosol phase nitrate to NOx changes our perspective of the NOx cycling chemistry in the tropical marine boundary layer, suggesting a more chemically complex environment than previously thought

Four years (2011–2015) of total gaseous mercury measurements from the Cape Verde Atmospheric Observatory

Mercury is a chemical with widespread anthropogenic emissions that is known to be highly toxic to humans, ecosystems and wildlife. Global anthropogenic emissions are around 20 % higher than natural emissions and the amount of mercury released into the atmosphere has increased since the industrial revolution. In 2005 the European Union and the United States adopted measures to reduce mercury use, in part to offset the impacts of increasing emissions in industrialising countries. The changing regional emissions of mercury have impacts on a range of spatial scales. Here we report 4 years (December 2011–December 2015) of total gaseous mercury (TGM) measurements at the Cape Verde Observatory (CVO), a global WMO-GAW station located in the subtropical remote marine boundary layer. Observed total gaseous mercury concentrations were between 1.03 and 1.33 ng m−3 (10th, 90th percentiles), close to expectations based on previous interhemispheric gradient measurements. We observe a decreasing trend in TGM (−0.05 ± 0.04 ng m−3 yr−1, −4.2 % ± 3.3 % yr−1) over the 4 years consistent with the reported decrease of mercury concentrations in North Atlantic surface waters and reductions in anthropogenic emissions. The decrease was more visible in the summer (July–September) than in the winter (December–February), when measurements were impacted by air from the African continent and Sahara/Sahel regions. African air masses were also associated with the highest and most variable TGM concentrations. We suggest that the less pronounced downward trend inclination in African air may be attributed to poorly controlled anthropogenic sources such as artisanal and small-scale gold mining (ASGM) in West Africa

Global impact of nitrate photolysis in sea-salt aerosol on NOx, OH, and O3 in the marine boundary layer

Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer (MBL) using the GEOS-Chem model, after first updating the model to better simulate observed gas-particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25-50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurements of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This under-prediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs : HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5 to 20 for NOx, 1.2 to 1.6 for OH, and 1.1 to 1.3 for ozone. Since the spatial extent of the sea-salt aerosol (SSA) impact is limited, global impacts on NOx, ozone, and OH mass burdens are small ( ∼ 1-3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry

Long-term NOx measurements in the remote marine tropical troposphere

Atmospheric nitrogen oxides (NO + NO2 = NOx) have been measured at the Cape Verde Atmospheric Observatory (CVAO) in the tropical Atlantic (16∘51′ N, 24∘52′ W) since October 2006. These measurements represent a unique time series of NOx in the background remote troposphere. Nitrogen dioxide (NO2) is measured via photolytic conversion to nitric oxide (NO) by ultraviolet light-emitting diode arrays followed by chemiluminescence detection. Since the measurements began, a blue light converter (BLC) has been used for NO2 photolysis, with a maximum spectral output of 395 nm from 2006 to 2015 and of 385 nm from 2015 onwards. The original BLC used was constructed with a Teflon-like material and appeared to cause an overestimation of NO2 when illuminated. To avoid such interferences, a new additional photolytic converter (PLC) with a quartz photolysis cell (maximum spectral output also 385 nm) was implemented in March 2017. Once corrections are made for the NO2 artefact from the original BLC, the two NO2 converters are shown to give comparable NO2 mixing ratios (BLC = 0.99 × PLC + 0.7 ppt, linear least-squares regression), giving confidence in the quantitative measurement of NOx at very low levels. Data analysis methods for the NOx measurements made at CVAO have been developed and applied to the entire time series to produce an internally consistent and high-quality long-term data set. NO has a clear diurnal pattern with a maximum mixing ratio of 2–10 ppt during the day depending on the season and ∼ 0 ppt during the night. NO2 shows a fairly flat diurnal signal, although a small increase in daytime NOx is evident in some months. Monthly average mixing ratios of NO2 vary between 5 and 30 ppt depending on the season. Clear seasonal trends in NO and NO2 levels can be observed with a maximum in autumn and winter and a minimum in spring and summer.</p

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

Discrepancy between simulated and observed ethane and propane levels explained by underestimated fossil emissions

Ethane and propane are the most abundant non-methane hydrocarbons in the atmosphere. However, their emissions, atmospheric distribution, and trends in their atmospheric concentrations are insufficiently understood. Atmospheric model simulations using standard community emission inventories do not reproduce available measurements in the Northern Hemisphere. Here, we show that observations of pre-industrial and present-day ethane and propane can be reproduced in simulations with a detailed atmospheric chemistry transport model, provided that natural geologic emissions are taken into account and anthropogenic fossil fuel emissions are assumed to be two to three times higher than is indicated in current inventories. Accounting for these enhanced ethane and propane emissions results in simulated surface ozone concentrations that are 5–13% higher than previously assumed in some polluted regions in Asia. The improved correspondence with observed ethane and propane in model simulations with greater emissions suggests that the level of fossil (geologic + fossil fuel) methane emissions in current inventories may need re-evaluation

Extensive field evidence for the release of HONO from the photolysis of nitrate aerosols

Particulate nitrate ([Formula: see text]) has long been considered a permanent sink for NO(x) (NO and NO(2)), removing a gaseous pollutant that is central to air quality and that influences the global self-cleansing capacity of the atmosphere. Evidence is emerging that photolysis of [Formula: see text] can recycle HONO and NO(x) back to the gas phase with potentially important implications for tropospheric ozone and OH budgets; however, there are substantial discrepancies in “renoxification” photolysis rate constants. Using aircraft and ground-based HONO observations in the remote Atlantic troposphere, we show evidence for renoxification occurring on mixed marine aerosols with an efficiency that increases with relative humidity and decreases with the concentration of [Formula: see text] , thus largely reconciling the very large discrepancies in renoxification photolysis rate constants found across multiple laboratory and field studies. Active release of HONO from aerosol has important implications for atmospheric oxidants such as OH and O(3) in both polluted and clean environments

The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Functional analysis of liverworts in dual symbiosis with Glomeromycota and Mucoromycotina fungi under a simulated Palaeozoic CO2 decline.

Most land plants form mutualistic associations with arbuscular mycorrhizal fungi of the Glomeromycota, but recent studies have found that ancient plant lineages form mutualisms with Mucoromycotina fungi. Simultaneous associations with both fungal lineages have now been found in some plants, necessitating studies to understand the functional and evolutionary significance of these tripartite associations for the first time. We investigate the physiology and cytology of dual fungal symbioses in the early-diverging liverworts Allisonia and Neohodgsonia at modern and Palaeozoic-like elevated atmospheric CO2 concentrations under which they are thought to have evolved. We found enhanced carbon cost to liverworts with simultaneous Mucoromycotina and Glomeromycota associations, greater nutrient gain compared with those symbiotic with only one fungal group in previous experiments and contrasting responses to atmospheric CO2 among liverwort-fungal symbioses. In liverwort-Mucoromycotina symbioses, there is increased P-for-C and N-for-C exchange efficiency at 440 p.p.m. compared with 1500 p.p.m. CO2. In liverwort-Glomeromycota symbioses, P-for-C exchange is lower at ambient CO2 compared with elevated CO2. No characteristic cytologies of dual symbiosis were identified. We provide evidence of a distinct physiological niche for plant symbioses with Mucoromycotina fungi, giving novel insight into why dual symbioses with Mucoromycotina and Glomeromycota fungi persist to the present day.The ISME Journal advance online publication, 27 November 2015; doi:10.1038/ismej.2015.204