During April–May 2010 the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft flew 12 flights targeting volcanic ash clouds around the UK. The aircraft observed ash layers between altitudes of 2–8 km with peak mass concentrations typically between 200–2000μg/m3, as estimated from a Cloud and Aerosol Spectrometer (CAS). A peak value of 2000–5000 μg/m3 was observed over Scotland on 14 May 2010, although with considerable uncertainty due to the possible contamination by ice. Aerosol size distributions within ash clouds showed a fine mode (0.1–0.6 μm) associated with sulphuric acid and/or sulphate, and a coarse mode (0.6–35 μm) associated with ash. The ash mass was dominated by particles in the size range 1–10 μm (volume‐equivalent diameter), with a peak typically around 3–5μm. Electron‐microscope images and scattering patterns from the SID‐2H (Small Ice Detector) probe showed the highly irregular shape of the ash particles. Ash clouds were also accompanied by elevated levels of SO2 (10–100 ppbv), strong aerosol scattering (50–500 × 10−6 m−1), and low Ångstrom exponents (−0.5 to 0.4) from the 3‐wavelength nephelometer. Coarse‐mode mass specific aerosol extinction coefficients (kext), based on the CAS size distribution varied from 0.45–1.06 m2/g. A representative value of 0.6 m2/g is suggested for distal ash clouds (∼1000 km downwind) from this eruption.

Original article can be found at : http://www.sciencedirect.com/ Copyright ElsevierAngle-dependent light scattering measurements on single ice analogues crystals are described. Phase functions and degree of linear polarization are measured for electrodynamically levitated crystals. A procedure for randomizing particle orientation during levitation is demonstrated. The dependence of scattering on the shape, complexity and surface roughness of the crystals is examined. The phase functions from complex crystals with smooth surfaces show little dependence on shape. There is close agreement between the measured functions and the analytic phase function for ice clouds. However, rosettes with rough surfaces have qualitatively different phase functions, with raised side and back scattering. The asymmetry parameter is typically about 0.8??0.04 and 0.63??0.05 for smooth and rough crystals, respectively. The 22o halo peak is present for smooth rosettes and aggregates but absent for rough rosettes. Two-dimensional scattering patterns from several crystals in fixed orientations are also shown. The results suggest that it may be possible to use such patterns to discriminate not only between crystals of different shape but also to obtain some information on surface properties

The effects of radio-frequency-excited oxygen and hydrogen plasmas on gold island films with adsorbed CN-, thiophenate, or p-nitrobenzoate ions have been investigated by surface-enhanced Raman spectroscopy (SERS). An oxygen plasma caused oxidation of adsorbed CN- to Au(CN)4 -, and there was evidence of oxidation of the adsorption site gold atoms at the Au/p-nitrobenzoate surface, while in a hydrogen plasma Au(CN)4 - was reduced back to adsorbed CN-. No adsorbed oxidation or reduction products of thiophenate or p-nitrobenzoate were detected, however. Exposure of gold films to an oxygen or hydrogen plasma also caused partial removal of the adsorbates, though with some loss of SERS activity, and in a hydrogen plasma thiophenate was preferentially removed from a gold film with coadsorbed thiophenate and CN-. On silver films, hydrogen plasma treatment almost completely removed adsorbed CN- with only a small loss of SERS activity, but in an oxygen plasma the films were rapidly destroyed.

Abstract. The knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed-phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional lightscattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed-phase and cirrus clouds. The patterns are analysed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light-scattering properties and also similar causes. Overall, the in situ data are consistent, with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic air masses than in a continental, polluted one. Overall, the roughness and complexity are expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.

The simulated irradiances are less sensitive to particle shape than radiances. However, it is shown through modelling of the surface and top-of-atmosphere (TOA) DRE over all daylight hours that significant differences exist at TOA due to variation in the asymmetry parameter. The TOA short-wave diurnally averaged DRE was modelled as between 0 and -20 W m −2 depending on particle shape. A long-wave interferometer measured downwelling and upwelling radiances to derive surface emissivity across the window region. Measured nadir brightness temperatures from high level show signature of dust. A drop in brightness temperature of 14K was determined using modelled pristine-sky spectra. The modelled outgoing long-wave DRE due to dust from this case was +14 W m −2 averaged over 24 h, or +17 W m −2 per unit AOD. Modelling studies illustrate the sensitivity to aerosol refractive index and size distribution for both short-wave and long-wave DREs. Considering the full spectrum, a refractive index dataset from the literature has been selected that best represents the Saharan dust encountered during GERBILS.