Temporal and spatial characteristics of ozone depletion events from measurements in the Arctic

Following polar sunrise in the Arctic springtime, tropospheric ozone episodically decreases rapidly to near-zero levels during ozone depletion events (ODEs). Many uncertainties remain in our understanding of ODE characteristics, including the temporal and spatial scales, as well as environmental drivers. Measurements of ozone, bromine monoxide (BrO), and meteorology were obtained during several deployments of autonomous, ice-tethered buoys (O-Buoys) from both coastal sites and over the Arctic Ocean; these data were used to characterize observed ODEs. Detected decreases in surface ozone levels during the onset of ODEs corresponded to a median estimated apparent ozone depletion timescale (based on both chemistry and the advection of O₃-depleted air) of 11 h. If assumed to be dominated by chemical mechanisms, these timescales would correspond to larger-than-observed BrO mole fractions based on known chemistry and assumed other radical levels. Using backward air mass trajectories and an assumption that transport mechanisms dominate observations, the spatial scales for ODEs (defined by time periods in which ozone levels ≤15 nmol mol⁻¹) were estimated to be 877 km (median), while areas estimated to represent major ozone depletions (<10 nmol mol⁻¹) had dimensions of 282 km (median). These observations point to a heterogeneous boundary layer with localized regions of active, ozone-destroying halogen chemistry, interspersed among larger regions of previously depleted air that retain reduced ozone levels through hindered atmospheric mixing. Based on the estimated size distribution, Monte Carlo simulations showed it was statistically possible that all ODEs observed could have originated upwind, followed by transport to the measurement site. Local wind speed averages were low during most ODEs (median of ~3.6 m s⁻¹), and there was no apparent dependence on local temperature

Ion-beam-induced morphology on the surface of thin polymer films at low current density and high ion fluence

The effect of Xe+ bombardment on the surface morphology of four different polymers, polystyrene (PS), poly(phenylene oxide), polyisobutylene, and polydimethylsiloxane, was investigated in ion energy and fluence ranges of interest for secondary ion mass spectrometry depth-profiling analysis. Atomic force microscopy (AFM) was applied to analyze the surface topography of pristine and irradiated polymers. AFM analyses of nonirradiated polymer films showed a feature-free surface with different smoothness. We studied the influence of different Xe+ beam parameters, including the incidence angle, ion energy (660-4000 eV), current density (0.5 x 10(2) to 8.7 x 10(2) nA/cm(2)), and ion fluence (4 x 10(14) to 2 X 10(17) ion/cm(2)). Xe+ bombardment of PS with 3-4 keV at a high current density did not induce any change in the surface morphology. Similarly, for ion irradiation with lower energy, no surface morphology change was found with a current density higher than 2.6 x 10(2) nA/cm(2) and an ion fluence up to 4 x 10(16) ion/cm(2). However, Xe+ irradiation with a lower current density and a higher ion fluence led to topography development for all of the polymers. The roughness of the polymer surface increased, and well-defined patterns appeared. The surface roughness increased with ion irradiation fluence and with the decrease of the current density. A pattern orientation along the beam direction was visible for inclined incidence between 15 degrees and 45 degrees with respect to the surface normal. Orientation was not seen at normal incidence. The surface topography development could be explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam and redeposition-adsorption from the gas phase. Time-of-flight secondary ion mass spectrometry analyses of irradiated PS showed strong surface modifications of the molecular structure and the presence of new material. (C) 2000 John Wiley & Sons, Inc

Ozone in the boundary layer air over the Arctic Ocean: measurements during the TARA transpolar drift 2006–2008

International audienceA full year of measurements of surface ozone over the Arctic Ocean far removed from land is presented (81 N– 88 N latitude). The data were obtained during the drift of the French schooner TARA between September 2006 and January 2008, while frozen in the Arctic Ocean. The data confirm that long periods of virtually total absence of ozone occur in the spring (mid March to mid June) after Polar sunrise. At other times of the year, ozone concentrations are comparable to other oceanic observations with winter mole fractions of ca. 30–40 nmol mol−1 and summer minima of ca. 20 nmol mol−1. Contrary to earlier observations from ozone sonde data obtained at Arctic coastal observatories, the ambient temperature was well above −20 C during most ODEs (ozone depletion episodes). Backwards trajectory calculations suggest that during these ODEs the air had previously been in contact with the frozen ocean surface for several days and originated largely from the Siberian coast where several large open flaw leads and polynyas developed in the spring of 2007

Surface topography development of thin polystyrene films under low energy ion irradiation

Morphological changes of spin-coated thin polystyrene (PS) films due to low energy Xe+ bombardment in the energy range from 660 eV to 4 keV are investigated. These surface modifications are characterised by means of Atomic Force Microscopy (AFM). No significant topographical change between pristine and irradiated film surfaces is found for ion energy higher than 1.5 keV in the ion fluence range between 4 x 10(14) and 4 x 10(16) cm(-2). An increase of surface roughness is however obtained after ion bombardment for energy lower than 2 keV at the highest ion fluence. Moreover, a strong change of the morphology is observed after an irradiation with Xef for energy less than 1.25 keV, and ion fluences higher than 5x10(16) cm(-2). The surface roughness increases and well-defined features appear. Their evolution is followed as a function of the fluence in the 5 x 10(16)-2x 10(17) cm(-2) range for 1 keV Xe+ irradiation. ToF-SIMS analyses in area bombarded in such conditions reveal deep modifications of the surface composition and structure, indicating the formation of a Carbon Black form. The energy threshold observed for the development of surface morphology features is explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam. (C) 1999 Elsevier Science B.V. All rights reserved

Sulfur dioxide (SO₂) vertical column density measurements by Pandora spectrometer over the Canadian oil sands

Vertical column densities (VCDs) of SO₂ retrieved by a Pandora spectral sun photometer at Fort McKay, Alberta, Canada, from 2013 to 2015 were analysed. The Fort McKay site is located in the Canadian oil sands region, approximately 20 km north of two major SO₂ sources (upgraders), with total emission of about 45 kt yr⁻¹. Elevated SO₂ VCD values were frequently recorded by the instrument, with the highest values of about 9 Dobson Units (DU; DU  =  2.69 × 10¹⁶ molecules cm⁻²). Comparisons with co-located in situ measurements demonstrated that there was a very good correlation between VCDs and surface concentrations in some cases, while in other cases, elevated VCDs did not correspond to high surface concentrations, suggesting the plume was above the ground. Elevated VCDs and surface concentrations were observed when the wind direction was from south to southeast, i.e. from the direction of the two local SO₂ sources. The precision of the SO₂ measurements, estimated from parallel measurements by two Pandora instruments at Toronto, is 0.17 DU. The total uncertainty of Pandora SO₂ VCD, estimated using measurements when the wind direction was away from the sources, is less than 0.26 DU (1<i>σ</i>). Comparisons with integrated SO₂ profiles from concurrent aircraft measurements support these estimates

Development of an autonomous sea ice tethered buoy for the study of ocean-atmosphere-sea ice-snow pack interactions: the O-buoy

A buoy based instrument platform (the "O-buoy") was designed, constructed, and field tested for year-round measurement of ozone, bromine monoxide, carbon dioxide, and meteorological variables over Arctic sea ice. The O-buoy operated in an autonomous manner with daily, bi-directional data transmissions using Iridium satellite communication. The O-buoy was equipped with three power sources: primary lithium-ion battery packs, rechargeable lead acid packs, and solar panels that recharge the lead acid packs, and can fully power the O-buoy during summer operation. This system was designed to operate under the harsh conditions present in the Arctic, with minimal direct human interaction, to aid in our understanding of the atmospheric chemistry that occurs in this remote region of the world. The current design requires approximately yearly maintenance limited by the lifetime of the primary power supply. The O-buoy system was field tested in Elson Lagoon, Barrow, Alaska from February to May 2009, and deployed in the Beaufort Sea in October 2009. Here, we describe the design and present preliminary data