Temperature dependence of the contact angle for 1-propanol on silver and on sodium chloride substrate

Im Rahmen der präsentieren Diplomarbeit wurde der Kontaktwinkel zwischen 1-Propanol und Silber beziehungsweise Natriumchlorid und dessen Temperaturabhängigkeit mit unterschiedlichen Messmethoden untersucht. Innerhalb eines Temperaturbereiches von -7°C bis 35°C wurden Messungen mit einem Fa. Krüss K12 Tensiometer durchgeführt. Dabei wurden mit Hilfe der dynamischen Wilhelmy Methode Fortschreite- θa und Rückschreitewinkel θr innerhalb des oben angeführten Temperaturbereiches gemessen. Im Hinblick auf den Einfluss des Kontaktwinkels auf das Nukleationsverhalten von 1-Propanol-Dampf auf Salz beziehungsweise Silber wurden nur Fortschreitewinkel bei der Auswertung berücksichtig. Ergebnisse der 1-Propanol/Silber Messungen zeigen, dass zusätzliche Beschichtungen der Sterlingsilver Proben mit Silber p.A. nicht nur den Absolutwert des Fortschreitewinkels sondern auch dessen Temperaturabhängigkeit verringern. Dieses Verhalten könnte auf den abnehmenden Kupfergehalt in der Probenoberfläche mit zunehmender Anzahl von Silber p.A.-Schichten zurückgeführt werden. Aufgrund der statistischen Fehler der Einzelmessungen ist nicht auszuschließen dass der Fortschreitewinkel für 1-Propanol auf der am öftesten beschichteten Silberprobe innerhalb des gesamten Temperaturbereichs konstant 17.1° beträgt. Für 1-Propanol/NaCl Kontaktwinkelmessungen wurden sowohl die dynamische Wilhelmy als auch die Washburn Methode angewendet. Die dafür verwendeten Proben waren einerseits NaCl-Kristalle und andererseits via PVD NaCl-beschichtete Glasplatten. Alle Messungen ergaben einen Fortschreitewinkel von 0°. Entgegen theoretischer Erwartungen jedoch waren die Rückschreitewinkel fast immer größer als die Fortschreitewinkel. Dieses unerwartete Verhalten könnte auf Oberflächenrauhigkeit und damit verbundener Flüssigkeitsabsorption an der Probenoberfläche erklärt werden. Einzig die unbehandelte Salzplatte ergab sowohl für Fort- alsauch Rückschreitewinkel 0°. Da jedoch wie zuvor erwähnt nur der Fortschreitewinkel einen Einfluss auf das Nukleationsverhalten hat kann trotz der widersprüchlichen θr Ergebnisse gesagt werden, dass der Kontaktwinkel keine Temperaturabhängigkeit aufweist.In the present thesis contact angles and their temperature dependence are measured by independent methods. Measurements in a temperature range from -7°C to 35°C were performed using a tensiometer. Within the stated temperature range the Dynamic-Wilhelmy method was applied to determine the advancing θa as well as the receding angle θr whereas solely the advancing angle is of interest with respect to the influence on heterogeneous nucleation. Results for 1-propanol/silver measurements show that additional coatings of the sterling silver probes with silver p.A. not only decrease θa values but also their temperature dependence. The observed behaviour can be referred to a decreasing copper content in the solid surface with increasing number of coats. According to statistical errors it can not be excluded that the advancing angle for 1-propanol on silver (two times coated) remains 17,1° within the observed temperature range. In order to determine the contact angle between NaCl and 1-propanol the Dynamic-Wilhelmy and the Washburn method were applied. Probes were on the one hand made out of a NaCl-crystal and on the other hand produced by coating glass with NaCl-powder via PVD. All measurements resulted in an advancing angle of 0°. However the obtained θr almost always exceeded θa, what might be referred to surface roughness and therewith associated adsorption of the liquid at the solid surface. Solely measurements with untreated salt plates conform to the expected behaviour that θr amounts to 0° in agreement with θa. Anyhow a temperature dependence of the contact angle could not be determined

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

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

Rapid Measurement of Sub-Micrometer Aerosol Size Distribution using a Fast Integrated Mobility Spectrometer

Rapid measurement of submicron particle size distributions enables the characterization of aerosols with fast changing properties, and is often necessary for measurements onboard mobile platforms (e.g., research aircraft). Aerosol mobility size distribution is commonly measured by a scanning mobility particle sizer (SMPS), which relies on voltage scanning or stepping to classify particles of different sizes, and may take about 1 minute or longer to obtain a complete size spectrum of aerosol particles. The recently developed fast integrated mobility spectrometer (FIMS) with enhanced dynamic size range separates and detects particles from 10 to ~600 nm simultaneously, allowing submicron aerosol mobility size distributions to be captured at a time resolution of 1 s. In this study, we present a detailed data inversion routine for deriving aerosol size distribution from FIMS measurements of aerosols with a wide size range. The inversion routine takes into consideration the FIMS transfer function, particle penetration efficiency in the FIMS, and multiple charging of aerosols. The accuracy of the FIMS measurement is demonstrated by comparing parallel FIMS and SMPS measurements of stable aerosols with a wide range of size spectrum shapes, including ambient aerosols and aerosols classified by a differential mobility analyzer (DMA). The FIMS and SMPS-derived size distributions show excellent agreements for all aerosols tested. In addition, total number concentrations of ambient aerosols were integrated from 1 Hz FIMS size distributions, and compared with those directly measured by a condensation particle counter (CPC) operated in parallel. The integrated and measured total particle concentrations agree well within 6.5%

A Humidity-Controlled Fast Integrated Mobility Spectrometer (HFIMS) for Rapid Measurements of Particle Hygroscopic Growth

We present a humidity-controlled fast integrated mobility spectrometer (HFIMS) for rapid particle hygroscopicity measurements. The HFIMS consists of a differential mobility analyzer (DMA), a relative humidity (RH) control unit and a water-based FIMS (WFIMS) coupled in series. The WFIMS (Pinterich et al., 2017) combines the fast integrated mobility spectrometer (Kulkarni and Wang, 2006a, b) with laminar flow water condensation methodologies (Hering and Stolzenburg, 2005; Spielman et al., 2017). Inside the WFIMS, particles of different electrical mobilities are spatially separated in an electric field, condensationally enlarged and imaged to provide 1 Hz measurements of size distribution spanning a factor of ∼3 in particle diameter, which is sufficient to cover the entire range of growth factor (GF) for atmospheric aerosol particles at 90 % RH. By replacing the second DMA of a traditional hygroscopicity tandem DMA (HTDMA) system with the WFIMS, the HFIMS greatly increases the speed of particle growth factor measurement. The performance of the HFIMS was evaluated using NaCl particles with well-known hygroscopic growth behavior and further through measurements of ambient aerosols. Results show that the HFIMS can reproduce, within 2 %, the literature values for hygroscopic growth of NaCl particles. NaCl deliquescence was observed between 76 and 77 % RH in agreement with the theoretical value of 76.5 % (Ming and Russell, 2001), and efflorescence relative humidity (43 %) was found to lie within the RH range of 41 to 56 % reported in the literature. Ambient data indicate that the HFIMS can measure the hygroscopic growth of five standard dry particle sizes ranging from 35 to 165 nm within less than 3 min, which makes it about 1 order of magnitude faster than traditional HTDMA systems

Retrieval of High Time Resolution Growth Factor Probability Density Function from a Humidity-Controlled Fast Integrated Mobility Spectrometer

Hygroscopicity describes the tendency of aerosol particle to uptake water and is among the key parameters in determining the impact of atmospheric aerosols on global radiation and climate. A hygroscopicity tandem differential mobility analyzer (HTDMA) system is the most widely used instrument for determining the aerosol hygroscopic growth. Because of the time needed to scan the classifying voltage of the DMA, HTDMA measurement often requires a minimum of 30 min to characterize the particle hygroscopic growth at a single relative humidity for five to six different sizes. This slow speed is often inadequate for measurements onboard mobile platforms or when aerosols evolve rapidly. Recently, a humidity-controlled fast integrated mobility spectrometer (HFIMS) was developed for measuring the hygroscopic growth of particles. The measurement speed of the HFIMS is about one order of magnitude faster than that of the conventional HTDMA. In this work, a data inversion routine is developed to retrieve the growth factor probability density function (GF-PDF) of particles measured by the HFIMS. The inversion routine considers the transfer functions of the upstream DMA and the downstream water-based fast integrated mobility spectrometer (FIMS), and derives the GF-PDF that reproduces the measured responses of the HFIMS. The performance of the inversion routine is examined using ambient measurements with different assumptions for the spectral shape of the particle GF-PDF (multimodal lognormal or piecewise linear). The influences of the data inversion parameters and counting statistics on the inverted GF-PDFs were further investigated, and an approach to determine the optimized inversion parameters is presented