Climate impacts of atmospheric low volatility organic compounds

There exist huge gaps in the knowledge of how cloud-aerosol interaction affects climate. Consequently global models estimating the radiative forcing by anthropogenic aerosols show considerable discrepancy. Especially challenging to quantify is the role of volatile organic compounds in forming aerosol particles which can act as cloud condensation nuclei. Volatile organic compounds are emitted into the atmosphere in large quantities by biogenic and anthropogenic sources. In the atmosphere they undergo chemical oxidation reactions and typically produce products that are highly oxygenated and have lower volatility. Volatility of these highly oxygenated molecules span a wide range and determine the ease with which they transfer to the aerosol phase - either via participation in new particle formation or by contributing to the growth of bigger particles. The extent to which the highly oxygenated molecules contribute to new particle formation or their subsequent growth impacts the number concentration of cloud condensation nuclei in the atmosphere. Hence to accurately estimate cloud condensation nuclei, global models need to take into account the role of highly oxygenated molecules of varying volatility in modulating the atmospheric aerosol size distribution. In this thesis a new nucleation parameterisation based solely on highly oxygenated species of extremely low volatility is added to the model and its impact on the estimated cloud albedo effect is assessed. The nucleation mechanism is based on the findings of the CLOUD Experiment at CERN. The implementation of this new parameterisation reduces previous model estimates of cloud albedo forcing through its impact on the pre-industrial atmosphere. The thesis then goes on to introduce a new secondary aerosol formation scheme from highly oxygenated organic molecules based on the understanding of recent scientific advancements and assesses the effect of implementing the scheme on the estimated cloud albedo effect. Results show highly oxygenated molecules of semi-volatile nature play a significant role in determining the number concentration of cloud relevant particles. Although their higher volatility renders them incapable of new particle formation, their atmospheric abundance and contribution to the growth of particles which are relatively larger, provide an efficient pathway for producing cloud condensation nuclei in the atmosphere. Further, an ensemble of simulations are produced and analysed to explore a 6-D parameter space based on pre-defined uncertainty ranges of these highly oxygenated molecules. The work identifies plausible and implausible regions within the 6-D space, based on model-observation comparison against three model outputs - number concentration of all particles, number concentration of CCN-relevant sized particles and organic aerosol concentration. The work provides a top-down estimate of yields of highly oxygenated molecules (that contribute to SOA formation) based on model skill score against ground-based observations. Such yields are typically based on laboratory experiments and is broadly considered to be an important reason behind the failure of global models to estimate realistic mass of secondary organic aerosols produced in the atmosphere. The work particularly highlights the importance of simulating cluster growth from low-volatility organic compounds to account for atmospheric cloud droplets

Towards a Cost Metric for Nearest Neighbor Constraints in Reversible Circuits

Abstract. This work in progress report proposes a new metric for estimating nearest neighbor cost at the reversible circuit level. This is in contrast to existing literature where nearest neighbor constraints are usually considered at the quantum circuit level. In order to define the metric, investigations on a state-of-the-art reversible to quantum mapping scheme have been conducted. From the retrieved information, a proper estimation to be used as a cost metric has been obtained. Using the metric, it becomes possible for the first time to optimize a reversible circuit with respect to nearest neighbor constraints

Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of -30, -40 and -50°C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds

Observation of viscosity transition in alpha-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of alpha-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35aEuro-% at -10aEuro-A degrees C and 80aEuro-% at -38aEuro-A degrees C, confirming previous calculations of the viscosity-transition conditions. Consequently, alpha-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.Peer reviewe

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol-cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20-100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m-2 (27%) to -0.60 W m-2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

Phonological Development in Bangla: A Normative Study

This study investigates the various phonological processes operational in the speech of 90 native Bangla spoken children between the age of 3;0 – 3;11 years. The speech of all children was recorded during the administration of the developed word list and was transcribed for analysis. Equality of proportions was used to investigate the observed pattern of variation in speech.Overall this study has established two aspects of speech development: age at which the error patterns were suppressed and the percentage of children exhibiting the obtained phonological processes. Processes like medial consonant deletion, unstressed syllable deletion, /l/ deletion, vowel unrounding, alveolar fronting, denasalization, stopping (except stopping of affricates and fricatives), palatalization and monothongization were eliminated by 3 years 5 months, while nasalization, backing of stops, initial consonant deletion, and coalescence were not found in age beyond 3 years and 9 months. Processes like vowel rising, nasalization, stopping, nasal assimilation, stop assimilation, velar fronting, and deaffrication decreased significantly as the chronological age progressed from 3 to 4 years. Other processes like cluster reduction, epenthesis, final consonant deletion, deaspiration, /r/ deletion, affrication (of fricatives), liquid replacement, and fronting of retroflex were considered to persist beyond 4 years of age. The results however refute the fact that, the mastery of phonological system is completed by 4 years of age. Native Bangla speaking children continues to use simplification for clusters, final consonants, fricatives, liquids, retroflex sounds, and the aspirated counterparts of stops, even after the age of four.The results thus provide a profile of the underlying rules a typically developing child uses, which can be served as a basis for planning remediation. Also information about typical errors helps to delineate the normal course of acquisition; consequently, a child’s atypical phonologic development can be evaluated against normal or typical error patterns

An efficient memristor crossbar architecture for mapping Boolean functions using Binary Decision Diagrams (BDD)

The memristor is considered as the fourth fundamental circuit element along with resistor, capacitor and inductor. It is a two-terminal passive circuit element whose resistance value changes based on the amount of charge flowing through it. Another property of the memristor is that its resistance change is non-volatile in nature, and hence can be used for non-volatile memory applications. Researchers have been exploring memristors from various perspectives such as logic design and storage applications. In this paper, a slicing crossbar architecture for the efficient mapping of Boolean functions is proposed which exploits gate level parallelism using the memristor aided logic (MAGIC) design style. A Boolean function is first represented as a Binary Decision Diagram (BDD). The BDD nodes are expressed as netlists of NOR and NOT gates, and are mapped to the proposed slicing crossbar architecture with parallel node evaluation where possible. This is the first approach that combines BDD-based synthesis with MAGIC gate evaluation on memristor crossbar, while at the same time avoiding crossbar-related problems using a slicing architecture. Experimental evaluations on standard benchmark functions show considerable improvement in the solutions.This work was supported fully by the Department of Science and Technology, Government of India, for the project “Development of CAD Tools for Synthesis, Optimization and Verification of Digital Circuits using Memristors” (Grant No. INT/AUSTRIA/BMWF/P-02/2017), and by the Austrian Agency for International Cooperation in Education and Research (OeAD, Grant No. IN 08/2017)