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New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1,2,3,4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3–H2SO4–NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.
A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog, but how it occurs in cities is often puzzling. If the growth rates of urban particles are similar to those found in cleaner environments (1–10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below −15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid–base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms.
The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nano-particle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e. in conditions where neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.2 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.2 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.2 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from −25 ∘C to 25 ∘C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the single-digit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward.
Caspase-2 represents the most conserved member of the caspase family, which exhibits features of both initiator and effector caspases. Using ribonucleoprotein (RNP)-immunoprecipitation assay, we identified the proapoptotic caspase-2L encoding mRNA as a novel target of the ubiquitous RNA-binding protein HuR in DLD-1 colon carcinoma cells. Unexpectedly, crosslinking-RNP and RNA probe pull-down experiments revealed that HuR binds exclusively to the caspase-2-5' untranslated region (UTR) despite that the 3' UTR of the mRNA bears several adenylate- and uridylate-rich elements representing the prototypical HuR binding sites. By using RNAi-mediated loss-of-function approach, we observed that HuR regulates the mRNA and in turn the protein levels of caspase-2 in a negative manner. Silencing of HuR did not affect the stability of caspase-2 mRNA but resulted in an increased redistribution of caspase-2 transcripts from RNP particles to translational active polysomes implicating that HuR exerts a direct repressive effect on caspase-2 translation. Consistently, in vitro translation of a luciferase reporter gene under the control of an upstream caspase-2-5'UTR was strongly impaired after the addition of recombinant HuR, whereas translation of caspase-2 coding region without the 5'UTR is not affected by HuR confirming the functional role of the caspase-2-5'UTR. Functionally, an elevation in caspase-2 level by HuR knockdown correlated with an increased sensitivity of cells to apoptosis induced by staurosporine- and pore-forming toxins as implicated by their significant accumulation in the sub G1 phase and an increase in caspase-2, -3 and poly ADP-ribose polymerase cleavage, respectively. Importantly, HuR knockdown cells remained insensitive toward STS-induced apoptosis if cells were additionally transfected with caspase-2-specific siRNAs. Collectively, our findings support the hypothesis that HuR by acting as an endogenous inhibitor of caspase-2-driven apoptosis may essentially contribute to the antiapoptotic program of adenocarcinoma cells by HuR.
The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100Mo and of the unstable isotope 93Mo were measured at the LAND/R3B setup at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94Mo and 96,98Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.
Die vorliegende Arbeit beschäftigt sich mit automatischer Informationssuche in heterogenen medizinischen Datenquellen. Informationssuche beschreibt einen Vorgang zur Deckung eines vorhandenen Informationsbedarfs, der aus einem Mangel an Wissen resultiert. In der modernen medizinischen Praxis sind aktuelle Informationen zur optimalen Behandlung eines Patienten wichtig. Fehlen diese Informationen, resultieren negative Folgen für den Behandlungsprozess. Im Hinblick auf den ableitbaren Erkenntnisgewinn ist die Fülle an aktuellen medizinischen Informationen, die heute über Literatur- und Wissensdatenbanken im Internet zur Verfügung steht, eigentlich wünschenswert. Das gezielte Auffinden relevanter Informationen, die zum Kenntnisstand des Arztes und dem Problem des Patienten passen, ist aber mühsam, fehlerbehaftet und zeitaufwändig. Der Aufwand, problemspezifische Informationen zu finden, wird zusätzlich dadurch vergrößert, dass die vorhandenen medizinischen Informationsanbieter unterschiedliche Anfragesprachen zum Zugriff auf die Daten bereitstellen und sich die Struktur der angebotenen Informationen von Anbieter zu Anbieter unterscheidet. Zur Lösung dieser Problematik werden Verfahren untersucht, mit denen die Informationsrecherche automatisiert werden kann. Ausgehend von den Informationen in der elektronischen Patientenakte und den persönlichen Interessen des Arztes werden Suchanfragen automatisch generiert, an verschiedene Informationsanbieter versandt, und die Suchergebnisse anschließend bedarfsgerecht gefiltert präsentiert. Die so gewonnenen Informationen ergänzen die Inhalte der elektronischen Patientenakte. Für die Generierung von problemspezifischen Suchanfragen wird ein komplexes, universelles Verfahren auf der Basis von dynamischen Textgenerierungsmethoden mittels XML-Strukturen entwickelt. Als Grundlage dient eine formal definierte Beschreibung des Informationsinteresses. Daten aus der elektronischen Patientenakte und dem Interessenprofil des Arztes werden über sog. Datencontainer in die Beschreibung eingebettet. Die Auswertung der Datencontainer ergibt eine allgemeine Anfrage, die erst in einem weiteren Schritt in die spezifische Anfragesyntax der einzelnen Informationsanbieter transformiert wird. Als Informationsanbieter kommen sowohl Anbieter medizinischer Literaturdatenbanken als auch eine medizinische Suchmaschine für das World Wide Web zum Einsatz. Das Konzept der virtuellen Datenbank wird verwendet, um aus den Antworten der Informationsanbieter die jeweils erforderlichen Informationsbestandteile zu extrahieren und in ein universelles XML-Dokumentenformat zu integrieren. Der Arzt, der mit dem System arbeitet, erhält als Ergebnis einer Recherche eine einheitliche, übersichtsartige Darstellung der Suchergebnisse, unabhängig von der Struktur der Informationen. Die Realisierung erfolgt als Prototyp eines Informations-Agentensystems, das aus einer interaktiven und einer automatischen, im Hintergrund arbeitenden Komponente besteht.