Light scattering

About: Light scattering is a research topic. Over the lifetime, 37721 publications have been published within this topic receiving 861581 citations.

Aerosol backscatter fraction and single scattering albedo: Measured values and uncertainties at a coastal station in the Pacific Northwest

Abstract: Light scattering, hemispheric backscattering, and absorption properties of submicrometer and supermicrometer aerosol particles at low relative humidity and 550 nm wavelength are investigated as a function of air mass category during a 2-month campaign at a midlatitude Pacific coastal station at Cheeka Peak, Washington. The main source of uncertainty in single scattering albedo (ω) measurements, namely, the measurement of light absorption, is addressed by the deployment of three identical absorption photometers and by relying on a recent calibration of this device using direct optical measurements. The absorption photometer measurement is corrected for response to light scattering, and measurements of sea-salt aerosol in this campaign provide a partial validation of this correction. Scattering measurements by nephelometry are also corrected for known instrumental nonidealities. Uncertainties stemming from instrumental noise, drift, calibration, and correction factors are propagated to allow comparisons among air mass categories and with other data sets and, ultimately, to constrain the values of ω and other optical properties used in climate models. Marine aerosol over the midlatitude eastern Pacific is found to be weakly absorbing for the sub-μm component and virtually nonabsorbing for the super-μm component (separated at 1 μm, low-relative humidity, aerodynamic diameter). A distinct increase in sub-μm light extinction (especially absorption) observed during 2 days of sustained marine flow appears to be Asian pollution transported across the Pacific. Low levels of gaseous NO x during this period rule out nearby combustion sources, and low levels of particulate Fe, Al, and Si rule out a significant contribution from mineral dust. Excluding this episode, both scattering and absorption properties for marine sampling conditions are similar to those observed in the clean midlatitude Southern Hemisphere (Cape Grim, Tasmania). In general, continental influence, as indicated by trends over the air mass categories, tends to raise the backscatter ratio and lower ω. Light absorption values compared to previous marine and coastal measurements confirm the range of values found by others and the highly variable nature of this quantity.

Theory of Enhance I Light Scattering from Molecules Adsorbed at the Metal-Solution Interface

Abstract: We present a theory to explain the anomalous enhancement of light scattering from molecules adsorbed at a metal-solution interface. It is found that tunneling of electrons between a surface molecule and the metal induces a resonance at a point in the vicinity of the Fermi surface. A dynamical equilibrium due to photoionization and recombination stabilizes the system near resonance.

Direct evidence of dust growth in L183 from mid-infrared light scattering

Abstract: Context. Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence of larger grains has so far been gathered in near/mid infrared extinction and millimeter observations. Interpreting the data is, however, aggravated by the complex interplay of density and dust properties (as well as temperature for thermal emission). Aims. Direct evidence of larger particles can be derived from scattered mid-infrared (MIR) radiation from a molecular cloud observed in a spectral range where little or no emission from polycyclic aromatic hydrocarbons (PAHs) is expected. Methods. We present new Spitzer data of L183 in bands that are sensitive and insensitive to PAHs. The visual extinction AV map derived in a former paper was fitted by a series of 3D Gaussian distributions. For different dust models, we calculate the scattered MIR radiation images of structures that agree with the AV map and compare them to the Spitzer data. Results. The Spitzer data of L183 show emission in the 3.6 and 4.5 μm bands, while the 5.8 μm band shows slight absorption. The emission layer of stochastically heated particles should coincide with the layer of strongest scattering of optical interstellar radiation, which is seen as an outer surface on I band images different from the emission region seen in the Spitzer images. Moreover, PAH emission is expected to strongly increase from 4.5 to 5.8 μm, which is not seen. Hence, we interpret this emission to be MIR scattered light from grains located further inside the core, and call it ”coreshine”. Scattered light modeling when assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. In contrast, models with grains growing with density yield images with a flux and pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 μm. Conclusions. There is direct evidence of dust grain growth in the inner part of L183 from the scattered light MIR images seen by Spitzer.

Size, Stability, and Porosity of Mesoporous Nanoparticles Characterized with Light Scattering

Abstract: Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles’ properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.