Accommodation coefficient of HOBr on deliquescent sodium bromide aerosol particles

Uptake of HOBr on sea salt aerosol, sea salt brine or ice is believed to be a key process providing a source of photolabile bromine (Br₂) and sustaining ozone depletion cycles in the Arctic troposphere. In the present study, uptake of HOBr on sodium bromide (NaBr) aerosol particles was investigated at an extremely low HOBr concentration of 300 cm^-3 using the short-lived radioactive isotopes ^83-86Br. Under these conditions, at maximum one HOBr molecule was taken up per particle. The rate of uptake was clearly limited by the mass accommodation coefficient, which was calculated to be 0.6 ± 0.2. This value is a factor of 10 larger than estimates used in earlier models. The atmospheric implications are discussed using the box model "MOCCA'', showing that the increase of the accommodation coefficient of HOBr by a factor of 10 only slightly affects net ozone loss, but significantly increases chlorine release

Isotope records from Mongolian and Alpine ice cores as climate indicators

The link between long term changes in the isotopic composition of precipitation and surface air temperature at a given location is of exceptional importance for paleoclimatic studies, as ahs been demonstrated by many recent publications based on the isotope records from polar ice cores. By means of direct comparison with instrumental data, this paper evaluates the potential of the deuterium and oxygen-18 records from two continental glaciers for monitoring climatic trends. The isotopic data presented characterize climatically contrasted enviroments. The records from the Swiss glacier show distinct seasonal variations. Oxygen-18 is fairly well correlated with the instrumental record of atmospheric temperature; the seasonal differences in deuterium excess reflect nearness to the oceanic moisture source. By contrast, the isotope data from the Mongolian site show poor correlation with atmospheric temperature. The seasonal variations in deuterium excess, with higher values during summer time, indicate that precipitation largely originates from re-evaporated continental moisture sources. In both cases however, the correlation with temperature is significantly improved by the elimination of values derived from years where major changes in seasonal distribution and/or snow loss obviously have occurred, thereby distoring the isotopic ratios for that particular year. Depending on the site selected for study, the stable isotope composition of ice cores should therefore be viewed not only as a proxy for atmospheric temperature, but also as an additional hydrometeorological parameter and source indicator for atmospheric moisture

Sources and distribution of trace species in Alpine precipitation inferred from two 60-year ice core paleorecords

International audienceThe Alps represent the largest barrier to meridional air flow in Europe, strongly influencing the weather and hence the distribution of atmospheric trace components. Here for the first time, chemical records from two ice cores retrieved from glaciers located in the northern and southern Swiss Alps were compared in conjunction with an analysis of "weather type", in order to assess geographical and seasonal trends in the deposition of trace species and to identify source regions and transport patterns. Using a correlation analysis, investigated trace species (NH4+, NO3?, SO42?, Ca2+, Mg2+, Na+, K+, and Cl? were grouped into classes of different origin (anthropogenic, sea salt, or Saharan dust). Over the last 60 years, precipitation chemistry at both sites was dominated by NH4+, NO4?, and SO42?, all of anthropogenic origin and deposited mainly in summer by way of convective precipitation. The similarity of the SO42? profiles with historical records of SO4 emissions from France and Italy indicated these two countries as key source areas for the anthropogenic species. In contrast, sea salt and Saharan dust showed major differences in transport pattern and deposition across the Alps. Currently, the sea-salt constituents Na+, K+, and Cl? are transported to the northern site during advective westerly-wind situations, independent of Saharan dust events. At the southern site, sea salt and Saharan dust are deposited simultaneously, indicating a coupled transport active mainly in summer during south-westerly wind situations

Prediction of the thermal release of transactinide elements (112 ≤ Z ≤ 116) from metals

Metallic catcher foils have been investigated on their thermal release capabilities for future superheavy element studies. These catcher materials shall serve as connection between production and chemical investigation of superheavy elements (SHE) at vacuum conditions. The diffusion constants and activation energies of diffusion have been extrapolated for various catcher materials using an atomic volume based model. Release rates can now be estimated for predefined experimental conditions using the determined diffusion values. The potential release behavior of the volatile SHE Cn (E112), E113, Fl (E114), E115, and Lv (E116) from polycrystalline, metallic foils of Ni, Y, Zr, Nb, Mo, Hf, Ta, and W is predicted. Example calculations showed that Zr is the best suited material in terms of on-line release efficiency and long-term operation stability. If higher temperatures up to 2773K are applicable, tungsten is suggested to be the material of choice for such experiment

Glacier mass balance reconstruction by sublimation induced enrichment of chemical species on Cerro Tapado (Chilean Andes)

A 36 m long ice core down to bedrock from the Cerro Tapado glacier (5536 m a.s.l, 30°08' S, 69°55' W) was analyzed to reconstruct past climatic conditions for Northern Chile. Because of the marked seasonality in the precipitation (short wet winter and extended dry summer periods) in this region, major snow ablation and related post-depositional processes occur on the glacier surface during summer periods. They include predominantly sublimation and dry deposition. Assuming that, like measured during the field campaign, the enrichment of chloride was always related to sublimation, the chemical record along the ice core may be applied to reconstruct the history of such secondary processes linked to the past climatic conditions over northern Chile. For the time period 1962–1999, a mean annual net accumulation of 316 mm water equivalent (weq) and 327 mm weq loss by sublimation was deduced by this method. This corresponds to an initial total annual accumulation of 539 mm weq. The annual variability of the accumulation and sublimation is related with the Southern Oscillation Index (SOI): higher net-accumulation during El-Niño years and more sublimation during La Niña years. The deepest part of the ice record shows a time discontinuity; with an ice body deposited under different climatic conditions: 290 mm higher precipitation but with reduced seasonal distribution (+470 mm in winter and –180 mm in summer) and –3°C lower mean annual temperature. Unfortunately, its age is unknown. The comparison with regional proxy data however let us conclude that the glacier buildup did most likely occur after the dry mid-Holocene

Effect of humidity on nitric acid uptake to mineral dust aerosol particles

International audienceThis study presents the first laboratory observation of HNO3 uptake by airborne mineral dust particles. The model aerosols were generated by dry dispersion of Arizona Test Dust (ATD), SiO2, and by nebulizing a saturated solution of calcium carbonate. The uptake of 13N-labeled gaseous nitric acid was observed in a flow reactor on the 0.2?2 s reaction time scale at room temperature and atmospheric pressure. The amount of nitric acid appearing in the aerosol phase at the end of the flow tube was found to be a linear function of the aerosol surface area. SiO2 particles did not show any significant uptake, while the CaCO3 aerosol was found to be more reactive than ATD. Due to the smaller uncertainty associated with the reactive surface area in the case of suspended particles as compared to bulk powder samples, we believe that we provide an improved estimate of the rate of uptake of HNO3 to mineral dust. The fact that the rate of uptake was smaller at a concentration of 1012 than at 1011 was indicative of a complex uptake mechanism. The uptake coefficient averaged over the first 2 s of reaction time at a concentration of 1012 molecules cm-3 was found to increase with increasing relative humidity, from 0.022±0.007 at 12% RH to 0.113±0.017 at 73% RH , which was attributed to an increasing degree of solvation of the more basic minerals. The extended processing of the dust by higher concentrations of HNO3 at 85% RH led to a water soluble coating on the particles and enhanced their hygroscopicity