Frequency response of an atomic force microscope in liquids and air: Magnetic versus acoustic excitation

We discuss the dynamics of an amplitude modulation atomic force microscope in different environments such as water and air. Experiments, analytical expressions, and numerical simulations show that the resonance curves depend on the excitation method used to drive the cantilever, either mechanical or magnetic. This dependence is magnified for small force constants and quality factors, i.e., below 1 N/m and 10, respectively. We show that the equation for the observable, the cantilever deflection, depends on the excitation method. Under mechanical excitation, the deflection involves the base and tip displacements, while in magnetic excitation, the cantilever deflection and tip displacement coincideThis work was financially supported by the European Commission (FORCETOOL) and the Ministerio de Educación y Ciencia (MAT2006-03833). We do thank stimulating discussions with J.R. Lozano, S. Patil and N.F. Martinez.Peer reviewe

The Light Absorption Heating Method for Measurement of Light Absorption by Particles Collected on Filters

A new instrument for the quantification of light absorption by particles collected on filters has been developed to address long standing environmental questions about light-absorbing particles in air, water, and on snow and ice. The Light Absorption Heating Method (LAHM) uses temperature changes when filters are exposed to light to quantify absorption. Through the use of calibration standards, the observed temperature response of unknown materials can be related to the absorption cross section of the substance collected on the filter. Here, we present a detailed description of the instrument and calibration. The results of the calibration tests using a common surrogate for black carbon, Fullerene soot, show that the instrument provides stable results even when exposed to adverse laboratory conditions, and that there is little drift in the instrument over longer periods of time. Calibration studies using Fullerene soot suspended in water, airborne propane soot, as well as atmospheric particulates show consistent results for absorption cross section when using accepted values for the mass absorption cross section of the soot and when compared to results from a 3-wavelength photoacoustic instrument. While filter sampling cannot provide the time resolution of other instrumentation, the LAHM instrument fills a niche where time averaging is reasonable and high-cost instrumentation is not available. The optimal range of absorption cross sections for LAHM is from 0.1 to 5.0 cm$^{2}$ (~1.0–50.0 µg soot) for 25 mm filters and 0.4 to 20 cm$^{2}$ (4.0–200.0 µg soot) for 47 mm filters, with reduced sensitivity to higher values

Specifying the light-absorbing properties of aerosol particles in fresh snow samples, collected at the Environmental Research Station Schneefernerhaus (UFS), Zugspitze

Atmospheric aerosol particles like mineral dust, volcanic ash and combustion particles can reduce Earth’s snow and ice albedo considerably even by very small amounts of deposited particle mass. In this study, a new laboratory method is applied to measure the spectral light absorption coefficient of airborne particles that are released from fresh snow samples by an efficient nebulizing system. Threewavelength photoacoustic absorption spectroscopy is combined with refractory black carbon (BC) mass analysis to determine the snow mass-specific and BC mass-specific absorption cross sections. Fullerene soot in water suspensions are used for the characterization of the method and for the determination of the mass-specific absorption cross section of this BC reference material. The analysis of 31 snow samples collected after fresh snowfall events at a high-altitude Alpine research station reveals a significant discrepancy between the measured snow mass-specific absorption cross section and the cross section that is expected from the BC mass data, indicating that non-BC light-absorbing particles are present in the snow. Mineral dust and brown carbon (BrC) are identified as possible candidates for the non-BC particle mass based on the wavelength dependence of the measured absorption. For one sample this result is confirmed by environmental scanning electron microscopy and by single-particle fluorescence measurements, which both indicate a high fraction of biogenic and organic particle mass in the sample

The four-wavelength Photoacoustic Aerosol Absorption Spectrometer (PAAS-4 λ )

In this paper, the Photoacoustic Aerosol Absorption Spectrometer (PAAS-4λ) is introduced. PAAS-4λ was specifically developed for long-term monitoring tasks in (unattended) air quality stations. It uses four wavelengths coupled to a single acoustic resonator in a compact and robust set-up. The instrument has been thoroughly characterized and carefully calibrated in the laboratory using NO$_2$/air mixtures and Nigrosin aerosol. It has an ultimate 1σ detection limit below 0.1 Mm$^{−1}$, at a measurement precision and accuracy of 3 % and 10 %, respectively. In order to demonstrate the PAAS-4λ suitability for long-term monitoring tasks, the instrument is currently validated at the air quality monitoring station Pallas in Finland, about 140 km north of the Arctic circle. A total of 11 months of PAAS-4λ data from this deployment are presented and discussed in terms of instrument performance. Intercomparisons with the filter-based photometers of a continuous soot monitoring system (COSMOS), the Multi-Angle Absorption Photometer (MAAP), and Aethalometer (AE33) demonstrate the capabilities and value of PAAS-4λ, as well as for the validation of the widely used filter-based instruments

Страховая деятельность в России на примере компании Росгосстрах

Объектом исследования является рынок страховых услуг РФ. Предметом рынок страховых услуг в экономике и страхование жизни и здоровья людей.The object of study is the market of insurance services of the Russian Federation. The subject of the insurance market in the economy and the insurance of life and health of peopl

Light absorbing properties of particles extracted from snow samples

Although BC is the dominating absorbing component in the atmosphere, there is evidence of numerous other aerosol components which are able to contribute to the aerosol light absorption. Such non-BC particles include mineral dust, volcanic ash, brown carbon as well as biological debris. Sooner or later different physical processes remove these airborne particles from the atmosphere and deposit them on the ground. If they are deposited on snow or ice surfaces these particles might induce melting processes by the absorption of solar radiation. Because snow is the most reflective natural surface on earth, already small amounts of absorptive impurities can significantly reduce the surface albedo. The contribution of the albedo reduction on the radiative balance of the atmosphere is usually assessed based on the mass concentration of refractory BC deposited in the snow. Ignoring the absorption contribution of the non-BC aerosol components might result in an underestimation of the albedo reduction. Therefore, the knowledge of the visible absorption coefficients of aerosol particles deposited in snow and ice, is essential for a realistic evaluation of the albedo effect on regional and global climate. To specify the absorbing properties of particles trapped in snow samples, we combined photo acoustic absorption spectroscopy with single particle black carbon mass analysis using a Single Particle Soot Photometer (SP2). In this way, the aerosol absorption coefficients in the visible spectral range and the refractory black carbon mass could be simultaneously derived. This type of analysis is quite challenging because of the low particle mass concentrations typically present in natural snow samples. In a first case study we used a set of snow samples from the Environmental Research Station (UFS) Zugspitze. Our results show significantly enhanced light absorption of the particles released from the snow samples compared to the particle absorption that can be linked to the refractory black carbon mass in the snow. Further analyses revealed a substantial portion of biological material within the snow that could be cause for the observed additional aerosol absorption

Have genetic targets for faecal pollution diagnostics and source tracking revolutionised water quality analysis yet?

The impacts on faecal pollution analysis using nucleic acid-based methods, such as PCR and sequencing, in health-related water quality research were assessed by rigorous literature analysis. A wide range of application areas and study designs has been identified since the first application more than 30 years ago (>1,100 publications). Given the consistency of methods and assessment types, we suggest defining this emerging part of science as a new discipline: genetic faecal pollution diagnostics (GFPD) in health-related microbial water quality analysis. Undoubtedly, GFPD has already revolutionised faecal pollution detection and microbial source tracking, the current core applications. GFPD is also expanding to many other research areas, including infection and health risk assessment, evaluation of microbial water treatment, and support of wastewater surveillance. In addition, storage of DNA extracts allows for biobanking, which opens up new perspectives. The tools of GFPD can be combined with cultivation-based standardised faecal indicator enumeration, pathogen detection, and various environmental data types, in an integrated data analysis approach. This comprehensive meta-analysis provides the scientific status quo of this field, including trend analyses and literature statistics, outlining identified application areas, and discussing the benefits and challenges of nucleic acid-based analysis in GFPD