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Nielsen C.J.,University of Oslo | Herrmann H.,Leibniz Institute for Tropospheric Research | Weller C.,Leibniz Institute for Tropospheric Research
Chemical Society Reviews | Year: 2012

This critical review addresses the atmospheric gas phase and aqueous phase amine chemistry that is relevant to potential emissions from amine-based carbon capture and storage (CCS). The focus is on amine, nitrosamine and nitramine degradation, and nitrosamine and nitramine formation processes. A comparison between the relative importance of the various atmospheric sinks for amines, nitrosamines and nitramines is presented. © The Royal Society of Chemistry 2012.


News Article | November 23, 2016
Site: news.mit.edu

Every year, trade winds over the Sahara Desert sweep up huge plumes of mineral dust, transporting hundreds of teragrams — enough to fill 10 million dump trucks — across North Africa and over the Atlantic Ocean. This dust can be blown for thousands of kilometers and settle in places as far away as Florida and the Bahamas. The Sahara is the largest source of windblown dust to the Earth’s atmosphere. But researchers from MIT, Yale University, and elsewhere now report that the African plume was far less dusty between 5,000 and 11,000 years ago, containing only half the amount of dust that is transported today. In a paper published today in Science Advances, the researchers have reconstructed the African dust plume over the last 23,000 years and observed a dramatic reduction in dust beginning around 11,000 years ago. They say this weakened plume may have allowed more sunlight to reach the ocean, increasing its temperature by 0.15 degrees Celsius — a small but significant spike that likely helped whip up monsoons over North Africa, where climate at the time was far more temperate and hospitable than it is today. “In the tropical ocean, fractions of a degree can cause big differences in precipitation patterns and winds,” says co-author David McGee, the Kerr-McGee Career Development Assistant Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “It does seem like dust variations may have large enough effects that it’s important to know how big those impacts were in past and future climates.” McGee’s co-authors include lead author Ross Williams, a former graduate student at MIT; along with Christopher Kinsley, Irit Tal, and David Ridley from MIT; Shineng Hu and Alexey Fedorov from Yale University; Richard Murray from Boston University; and Peter deMenocal from Columbia University. Around 11,000 years ago, the Earth had just emerged from the last ice age and was beginning a new, interglacial epoch known as the Holocene. Geologists and archaeologists have found evidence that during this period the Sahara was much greener, wetter, and more livable than it is today. “There was also extensive human settlement throughout the Sahara, with lifestyles that would never be possible today,” McGee says. “Researchers at archaeological sites have found fish hooks and spears in the middle of the Sahara, in places that would be completely uninhabitable today. So there was clearly much more water and precipitation over the Sahara.” This evidence of wet conditions shows that the region experienced regular monsoon rains during the early Holocene. This was primarily due to the slow wobbling of Earth’s axis, which exposed the Northern Hemisphere to more sunlight during summer; this, in turn, warmed the land and ocean and drew more water vapor — and precipitation — over North Africa. Increased vegetation in the Sahara may have also played a role, absorbing sunlight and heating the surface, drawing more moisture over the land. “The mysterious thing is, if you try to simulate all these changes in these early and mid-Holocene climates, the models intensify the monsoons, but nowhere near the amounts suggested by the paleodata,” McGee says. “One of the things not factored into these simulations is changes in windblown dust.” In their results published today, McGee and colleagues propose a reduction in African dust may indeed have contributed to increasing monsoon rains in the region. The researchers came to their conclusion after estimating the amount of long-range windblown dust emitted from Africa over the last 23,000 years, from the end of the last ice age to today. They focused on dust transported long distances, as these particles are small and light enough to be lifted and carried through the atmosphere for days before settling thousands of kilometers away from their source. This fine-grained dust scatters incoming solar radiation, cooling the ocean’s surface and potentially affecting precipitation patterns, depending on how much dust is in the air. To estimate how the African dust plume has changed over thousands of years, the team looked for places where dust should accumulate rapidly. Dust can sink to the floor of open ocean, but there layers of sediment build up very slowly, at a rate of 1 centimeter every 1,000 years. Places like the Bahamas, by contrast, accumulate sediment much more quickly, making it easier for scientists to determine the ages of particular sediment layers. What’s more, it’s been shown that most of the windblown dust that has accumulated in the Bahamas originated not from local regions such as the U.S., but from the Sahara. McGee and his colleagues obtained sediment core samples from the Bahamas that were collected in the 1980s by scientists from the Woods Hole Oceanographic Institution. They brought the samples back to the lab and analyzed their chemical composition, including isotopes of thorium — an element that exists in windblown dust worldwide, at known concentrations. They determined how much dust was in each sediment layer by measuring the primary isotope of thorium, and determined how fast it was accumulating by measuring the amount of a rare thorium isotope in each layer. In this way, the team analyzed sediment layers from the last 23,000 years, and showed that around 16,000 years ago, toward the end of the last ice age, the dust plume was at its highest, lofting at least twice the amount of dust over the Atlantic, compared to today. However, between 5,000 and 11,000 years ago, this plume weakened significantly, with just half the amount of today’s windblown dust. Colleagues at Yale University then plugged their estimates into a climate model to see how such changes in the African dust plume would affect both ocean temperatures in the North Atlantic and overall climate in North Africa. The simulations showed that a drop in long-range windblown dust would raise sea surface temperatures by 0.15 degrees Celsius, drawing more water vapor over the Sahara, which would have helped to drive more intense monsoon rains in the region. “The modeling showed that if dust had even relatively small impacts on sea surface temperatures, this could have pronounced impacts on precipitation and winds both in the north Atlantic and over North Africa,” McGee says. Noting that the next key step is to reduce uncertainties in the modeling of dust’s climate impacts, he adds: “We’re not saying, the expansion of monsoon rains into the Sahara was caused solely by dust impacts. We’re saying we need to figure out how big those dust impacts are, to understand both past and future climates.” Ina Tegen, a professor at the Leibniz Institute for Tropospheric Research in Germany, says the group’s results suggest that “dust effects today may be considerable as well.” “Dust loads vary with changing climate, and due to the effects of dust on [solar] radiation, ice formation in clouds, and the carbon cycle, this may cause important climate  feedbacks,” says Tegen, who was not involved in the research. “The changing climate since the last ice age can be considered a ‘natural laboratory’ to study such effects. Understanding the past is the basis for predicting future changes with any confidence.” This research was supported, in part, by the National Science Foundation.


Mamouri R.E.,Cyprus University of Technology | Ansmann A.,Leibniz Institute for Tropospheric Research
Atmospheric Chemistry and Physics | Year: 2015

A lidar method is presented that permits the estimation of height profiles of ice nuclei concentrations (INC) in desert dust layers. The polarization lidar technique is applied to separate dust and non-dust backscatter and extinction coefficients. The desert dust extinction coefficients σd are then converted to aerosol particle number concentrations APC280 which consider particles with radius > 280 nm only. By using profiles of APC280 and ambient temperature T along the laser beam, the profile of INC can be estimated within a factor of 3 by means of APC-T-INC parameterizations from the literature. The observed close relationship between σd at 500 nm and APC280 is of key importance for a successful INC retrieval. We studied this link by means of AERONET (Aerosol Robotic Network) sun/sky photometer observations at Morocco, Cabo Verde, Barbados, and Cyprus during desert dust outbreaks. The new INC retrieval method is applied to lidar observations of dust layers with the spaceborne lidar CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) during two overpasses over the EARLINET (European Aerosol Research Lidar Network) lidar site of the Cyprus University of Technology (CUT), Limassol (34.7° N, 33° E), Cyprus. The good agreement between the CALIOP and CUT lidar retrievals of σd, APC280, and INC profiles corroborates the potential of CALIOP to provide 3-D global desert dust APC280 and INC data sets. © Author(s) 2015.


Grant
Agency: GTR | Branch: NERC | Program: | Phase: Research Grant | Award Amount: 864.10K | Year: 2011

Aerosol particles act as sites for cloud droplet and ice particle formation. Cloud properties can be perturbed through the addition of aerosol particles into the atmosphere from anthropogenic and natural processes. This addition influences cloud microphysical properties, and subsequently affects cloud dynamics and thermodynamics, and the way the cloud interacts with radiation. The Earths radiation budget is very greatly affected by clouds, and human-induced changes to the particle loading affecting them, known as indirect effects, are large and highly uncertain. A large part of this uncertainty is the result of poor knowledge of the fundamental aerosol and cloud properties and processes, leading to their poor representation in models. A programme of research is proposed here to i) directly investigate these processes in the laboratory, ii) evaluate the sensitivity of climate relevant parameters to the studied processes, iii) interpret the laboratory studies with detailed model investigations and iv) to incorporate and test new descriptions of the studied processes in cloud-scale and, where possible, global scale models. The programme will thereby reduce the uncertainty in estimates of radiative forcing and climate feedbacks relating to aerosol and cloud processes. The studies are split into those affecting warm clouds (those containing only liquid droplets) and those affecting clouds containing ice particles. The programme brings together an interdisciplinary team of researchers with expertise in warm and cold cloud and aerosol processes combining laboratory and multiscale modelling activities to deliver the improved predictive capability. The warm laboratory work focuses on two major aspects i) the rate at which water is taken up by growing aerosol particles as they become cloud droplets (or activate) and ii) the ability of aerosol particles of various compositions to act as seeds for cloud droplets. These studies use a number of techniques including single particle optical levitation and investigations in a large photochemical chamber coupled to a large number of chemical and physical probes of ensembles of particles formed in simulated atmospheric chemical processes. The cold work uses a similar coupling of a large, well-instrumented cloud chamber experiments and single particle levitation studies. The chambers used in both aspects will be coupled to investigate the impacts of aerosol transformation conditions on warm and cold cloud formation, using the instrumental payload from both chambers. A range of detailed models will be used to explicitly describe the processes by which aerosol particles interact with increasing relative humidity and reducing temperature to form cloud droplet and ice crystals and to their properties. The processes and properties will be represented in dynamical frameworks to predict the interactions between aerosols and clouds and their radiative effects at cloud resolving scales and radiative forcing of some of the investigated properties on global radiative forcing and feedbacks. The sensitivity of climate relevant parameters to the fundamental parameters investigated in the laboratory programme and their improved quantification will be evaluated using a simplified model emulator.


News Article | November 4, 2016
Site: www.eurekalert.org

Leipzig. The formation of sulfur dioxide from the oxidation of dimethyl sulfide (DMS) and, thus, of cooling clouds over the oceans seems to be overvalued in current climate models. This concludes scientists from the Leibniz Institute for Tropospheric Research (TROPOS) from a model study on the effects of DMS on atmospheric chemistry. Until now, models considering only the oxidation in the gas phase describe merely the oxidation pathway and neglect important pathways in the aqueous phase of the atmosphere, writes the team in the journal PNAS. This publication contains until now the most comprehensive mechanistic study on the multiphase oxidation of this compound. The results have shown that in order to improve the understanding of the atmospheric chemistry and its climate effects over the oceans, a more detailed knowledge about the multiphase oxidation of DMS and its oxidation products is necessary. Furthermore, it is also needed to increase the accuracy of climate prediction. Dimethyl sulfide (DMS) is formed by microorganisms and is, for example, also part of human breath odor. However, it is more pleasant to remember as the typical smell of the sea. DMS represents the most common natural sulfur compound emitted to the atmosphere. Major contributors are oceans, which make up around 70 % of Earth's surface. DMS is formed by phytoplankton and then released from the seawater. In the atmosphere, DMS oxidizes to sulfuric acid (H2SO4) via dimethyl sulfoxide (DMSO) and sulfur dioxide (SO2). Sulfuric acid can form new cloud nuclei, from which new cloud droplets can emerge. Hence, marine clouds will be visually brightened, which influences the radiative effect of clouds and thus Earth's climate. Therefore, the understanding and quantification of these chemical processes in the atmosphere is of high importance for the knowledge of the natural climate effect. The oxidation process of DMS has already been investigated in various model studies - albeit without accurate considered aqueous-phase chemistry. In order to close these mechanistic gaps, scientists of TROPOS have developed a comprehensive multiphase chemical mechanism ("Chemical Aqueous Phase Radical Mechanism DMS Module 1.0"). This mechanism was coupled to a comprehensive gas-phase (MCMv3.2) and aqueous-phase mechanism (CAPRAM) and applied with the SPACCIM model. The SPACCIM model was developed at TROPOS and is, due to the detailed and combined description of microphysical and chemical processes in aerosols and clouds, particularly suitable for complex studies on atmospheric multiphase processes. As most important outcome, the new model results showed that: "The processes in the aqueous phase significantly reduce the amount of sulfur dioxide and increase the amount of methanesulfonic acid (MSA). In earlier models, there was a gap between the projected values in the model and measurements. Now, the scientists have been able to clarify this contradiction and thus confirm the importance of the aqueous phase for the atmospheric oxidation of dimethyl sulfide and its products such as MSA", reports Dr. Andreas Tilgner of TROPOS. The results show that the role of DMS in Earth's climate is still not sufficiently understood - despite many global model studies. "Our simulations indicate that the increased DMS emissions lead to higher aerosol particle mass loads but not necessarily to a higher number of particles or cloud droplets. The modeling results are important to understand the climate processes between ocean and atmosphere. In addition, geoengineering ideas are constantly being discussed, which are hoping for more cooling clouds by fertilizing the ocean", explains Prof. Hartmut Herrmann from TROPOS. However, this study suggests that the production of sulfur dioxide is less pronounced and the effects on the back-reflection effect of the clouds are lower than expected. Therefore, the corresponding geoengineering approaches could be less effective than assumed. Tilo Arnhold Erik Hans Hoffmann, Andreas Tilgner, Roland Schrödner, Peter Bräuer, Ralf Wolke, and Hartmut Herrmann (2016): An advanced modeling study on the impacts and atmospheric implications of multiphase dimethyl sulfide chemistry. PNAS; 113 (42) 11776-11781, doi: 10.1073/pnas.1606320113 Surface of the oceans affects climate more than thought (press release, 30 Sep 2015) https:/ The Leibniz Association connects 88 independent research institutions that range in focus from the natural, engineering and environmental sciences via economics, spatial and social sciences to the humanities. Leibniz institutes address issues of social, economic and ecological relevance. They conduct knowledge-driven and applied basic research, maintain scientific infrastructure and provide research-based services. The Leibniz Association identifies focus areas for knowledge transfer to policy-makers, academia, business and the public. Leibniz institutions collaborate intensively with universities - in the form of "Leibniz ScienceCampi" (thematic partnerships between university and non-university research institutes), for example - as well as with industry and other partners at home and abroad. They are subject to an independent evaluation procedure that is unparalleled in its transparency. Due to the importance of the institutions for the country as a whole, they are funded jointly by the Federation and the Länder, employing some 18,500 individuals, including 9,300 researchers. The entire budget of all the institutes is approximately 1.7 billion EUR. http://www.


News Article | November 4, 2016
Site: www.sciencedaily.com

The formation of sulfur dioxide from the oxidation of dimethyl sulfide (DMS) and, thus, of cooling clouds over the oceans seems to be overvalued in current climate models. This concludes scientists from the Leibniz Institute for Tropospheric Research (TROPOS) from a model study on the effects of DMS on atmospheric chemistry. Until now, models considering only the oxidation in the gas phase describe merely the oxidation pathway and neglect important pathways in the aqueous phase of the atmosphere, writes the team in the journal PNAS. This publication contains until now the most comprehensive mechanistic study on the multiphase oxidation of this compound. The results have shown that in order to improve the understanding of the atmospheric chemistry and its climate effects over the oceans, a more detailed knowledge about the multiphase oxidation of DMS and its oxidation products is necessary. Furthermore, it is also needed to increase the accuracy of climate prediction. Dimethyl sulfide (DMS) is formed by microorganisms and is, for example, also part of human breath odor. However, it is more pleasant to remember as the typical smell of the sea. DMS represents the most common natural sulfur compound emitted to the atmosphere. Major contributors are oceans, which make up around 70 % of Earth's surface. DMS is formed by phytoplankton and then released from the seawater. In the atmosphere, DMS oxidizes to sulfuric acid (H2SO4) via dimethyl sulfoxide (DMSO) and sulfur dioxide (SO2). Sulfuric acid can form new cloud nuclei, from which new cloud droplets can emerge. Hence, marine clouds will be visually brightened, which influences the radiative effect of clouds and thus Earth's climate. Therefore, the understanding and quantification of these chemical processes in the atmosphere is of high importance for the knowledge of the natural climate effect. The oxidation process of DMS has already been investigated in various model studies -- albeit without accurate considered aqueous-phase chemistry. In order to close these mechanistic gaps, scientists of TROPOS have developed a comprehensive multiphase chemical mechanism ("Chemical Aqueous Phase Radical Mechanism DMS Module 1.0"). This mechanism was coupled to a comprehensive gas-phase (MCMv3.2) and aqueous-phase mechanism (CAPRAM) and applied with the SPACCIM model. The SPACCIM model was developed at TROPOS and is, due to the detailed and combined description of microphysical and chemical processes in aerosols and clouds, particularly suitable for complex studies on atmospheric multiphase processes. As most important outcome, the new model results showed that: "The processes in the aqueous phase significantly reduce the amount of sulfur dioxide and increase the amount of methanesulfonic acid (MSA). In earlier models, there was a gap between the projected values in the model and measurements. Now, the scientists have been able to clarify this contradiction and thus confirm the importance of the aqueous phase for the atmospheric oxidation of dimethyl sulfide and its products such as MSA," reports Dr. Andreas Tilgner of TROPOS. The results show that the role of DMS in Earth's climate is still not sufficiently understood -- despite many global model studies. "Our simulations indicate that the increased DMS emissions lead to higher aerosol particle mass loads but not necessarily to a higher number of particles or cloud droplets. The modeling results are important to understand the climate processes between ocean and atmosphere. In addition, geoengineering ideas are constantly being discussed, which are hoping for more cooling clouds by fertilizing the ocean," explains Prof. Hartmut Herrmann from TROPOS. However, this study suggests that the production of sulfur dioxide is less pronounced and the effects on the back-reflection effect of the clouds are lower than expected. Therefore, the corresponding geoengineering approaches could be less effective than assumed.


Tilgner A.,Leibniz Institute for Tropospheric Research | Herrmann H.,Leibniz Institute for Tropospheric Research
Atmospheric Environment | Year: 2010

Model studies on the aqueous phase radical-driven processing of carbonyl compounds and acids in clouds and deliquescent particles were performed. The model exposed that aqueous radical conversions of carbonyl compounds and its oxidation products can contribute potentially to the formation of functionalised organic acids. The main identified C2-C4 organic gas phase precursors are ethylene glycol, glycolaldehyde, glyoxal, methylglyoxal and 1,4-butenedial. The aqueous phase is shown to contribute significantly with about 93%/63%, 47%/8%, 31%/4%, 7%/4%, 36%/8% to the multiphase oxidative fate of these compounds under remote/urban conditions. Interestingly, the studies revealed that aqueous chemical processing is not only limited to in-cloud conditions but also proceeds in deliquescent particle phase with significant fluxes. Oxalic acid is shown to be formed preferably in deliquescent particles subsequent to the in-cloud oxidations. Mean aqueous phase oxalate formation fluxes of about 12, 42 and 0.4ngm-3h-1 in the remote, urban and maritime scenario, respectively. Additionally, the turnovers of the oxidation of organics such as methylglyoxal by NO3 radical reactions are identified to be competitive to their OH pendants. At the current state of CAPRAM, mean C2-C4 in-cloud oxidation fluxes of about 0.12 and 0.5μgm-3h-1 are modelled under the idealised remote and urban cloud conditions. Finally, turnovers from radical oxidations were compared with those of thermal reactions. It is demonstrated that, based on the sparse kinetic data available organic accretion reaction might be of interest in just a few cases for cloud droplets and aqueous particles but generally do not reach the oxidative conversion rates of the main radical oxidants OH and NO3. Interestingly, oxidation reactions of H2O2 are shown to be competitive to the OH radical conversions in cases when H2O2 is not readily used up by the S(IV) oxidation. © 2010 Elsevier Ltd.


Horn S.,Leibniz Institute for Tropospheric Research
Geoscientific Model Development | Year: 2012

In this work the three dimensional compressible moist atmospheric model ASAMgpu is presented. The calculations are done using graphics processing units (GPUs). To ensure platform independence OpenGL and GLSL are used, with that the model runs on any hardware supporting fragment shaders. The MPICH2 library enables interprocess communication allowing the usage of more than one GPU through domain decomposition. Time integration is done with an explicit three step Runge-Kutta scheme with a time-splitting algorithm for the acoustic waves. The results for four test cases are shown in this paper. A rising dry heat bubble, a cold bubble induced density flow, a rising moist heat bubble in a saturated environment, and a DYCOMS-II case. © Author(s) 2012.


Heintzenberg J.,Leibniz Institute for Tropospheric Research | Leck C.,University of Stockholm
Atmospheric Chemistry and Physics | Year: 2012

In the course of global warming dramatic changes are taking place in the Arctic and boreal environments. However, physical aerosol data in from the central summer Arctic taken over the course of 18 yr from 1991 to 2008 do not show systematic year-to-year changes, albeit substantial interannual variations. Besides the limited extent of the data several causes may be responsible for these findings. The processes controlling concentrations and particle size distribution of the aerosol over the central Arctic perennial pack ice area, north of 80°, may not have changed substantially during this time. Environmental changes are still mainly effective in the marginal ice zone, the ice-free waters and continental rims and have not propagated significantly into the central Arctic yet where they could affect the local aerosol and its sources. The analysis of meteorological conditions of the four expedition summers reveal substantial variations which we see as main causes of the measured variations in aerosol parameters. With combined lognormal fits of the hourly number size distributions of the four expeditions representative mode parameters for the summer aerosol in the central Arctic have been calculated. The combined aerosol statistics discussed in the present paper provide comprehensive physical data on the summer aerosol in the central Arctic. These data are the only surface aerosol information from this region. © 2012 Author(s).


Schone L.,Leibniz Institute for Tropospheric Research | Herrmann H.,Leibniz Institute for Tropospheric Research
Atmospheric Chemistry and Physics | Year: 2014

Free radical reactions are an important degradation process for organic compounds within the aqueous atmospheric environment. Nevertheless, non-radical oxidants such as hydrogen peroxide and ozone also contribute to the degradation and conversion of these substances (Tilgner and Herrmann, 2010). In this work, kinetic investigations of non-radical reactions were conducted using UV / Vis spectroscopy (dual-beam spectrophotometer and stopped flow technique) and a capillary electrophoresis system applying pseudo-first order kinetics to reactions of glyoxal, methylglyoxal, glycolaldehyde, glyoxylic, pyruvic and glycolic acid as well as methacrolein (MACR) and methyl vinyl ketone (MVK) with H2O2 and ozone at 298 K. The measurements indicate rather small rate constants at room temperature of k2nd <3 Mg-1 sg -1 (except for the unsaturated compounds exposed to ozone). Compared to radical reaction rate constants the values are about 10 orders of magnitude smaller (kOH ∼109 Mg-1 sg-1). However, when considering the much larger non-radical oxidant concentrations compared to radical concentrations in urban cloud droplets, calculated first-order conversion rate constants change the picture towards H2O2 reactions becoming more important, especially when compared to the nitrate radical. For some reactions mechanistic suggestions are also given. © Author(s) 2014.

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