Susanne Preunkert

Levoglucosan levels at background sites in Europe for assessing the impact of biomass combustion on the European aerosol background

Atmospheric levoglucosan has been determined as a proxy for “biomass smoke” in samples from six background stations on a west–east transect extending from the Atlantic (Azores) to the mid-European background site KPZ (K-Puszta, Hungary). Concentration levels of levoglucosan (biannual averages) in the west–east transect range from 0.005 μg/m3 at the oceanic background site AZO (Azores) to 0.52 μg/m3 at AVE (Aveiro, Portugal). The atmospheric concentration of “biomass smoke” (biannual averages) was derived from the levoglucosan data with wood-type-specific conversion factors. Annual averages of wood smoke levels ranged from 0.05 μg/m3 at AZO to 4.3 μg/m3 at AVE. Winter (DJF) averages at the low-level sites AVE and KPZ were 10.8 and 6.7 μg/m3, respectively. Relative contributions of biomass smoke to organic matter (OM) range from around 9–11% at the elevated sites SIL, PDD and SBO, as well as for AZO, to 36% at the low-level site AVE and 28% at KPZ. Surprisingly high relative concentrations of biomass smoke in OM (68 and 47%) were observed for wintry conditions at the continental low-level CARBOSOL sites AVE and KPZ. Thus biomass smoke is a very important constituent of the organic material in the mid and west European background with summer contributions to organic matter of around 1–6% and winter levels of around 20% at the elevated mountain sites and 47–68% at rural flat terrain sites, not including secondary organic aerosol from biomass combustion sources.

Seasonal trends and possible sources of brown carbon based on 2-year aerosol measurements at six sites in Europe

Brown carbon is a ubiquitous and unidentified component of organic aerosol which has recently come into the forefront of atmospheric research. This component is strongly linked to the class of humic-like substances (HULIS) in aerosol whose ultimate origin is still being debated. Using a simplified spectroscopic method the concentrations of brown carbon have been determined in aqueous extracts of fine aerosol collected during the CARBOSOL project. On the basis of the results of 2-year measurements of several aerosol constituents at six European sites, possible sources of brown carbon are inferred. Biomass burning ( possibly domestic wood burning) is shown to be a major source of brown carbon in winter. At elevated sites in spring, smoke from agricultural fires may be an additional source. Direct comparison of measured brown carbon concentrations with HULIS determined by an independent method reveals that the two quantities correlate well at low-elevation sites throughout the year. At high-elevation sites the correlation is still high for winter but becomes markedly lower in summer, implying different sources and/or atmospheric sinks of brown carbon and HULIS. The results shed some light on the relationships between atmospheric brown carbon and HULIS, two ill-defined and overlapping components of organic aerosol.

Origin of C2–C5 dicarboxylic acids in the European atmosphere inferred from year‐round aerosol study conducted at a west‐east transect

[1] An atmospheric study of C 2 -C 5 dicarboxylic acids was conducted over two years at seven sites located from the Azores to eastern continental European sites. The lowest concentrations of total C 2 -C 5 diacids are observed at the Azores (Portugal) and at 4360 m elevation in the Alps (∼50 ng m -3 ), and the highest (400 ng m -3 ) are observed at the rural K-puszta site (Hungary). Quasi-absent at surface sites, the seasonal cycle of total diacids is characterized by a pronounced summer maximum at elevated sites, the highest summer level (510 ng m -3 ) being observed at the forested mountain site of Schauinsland (Germany). Whatever site and season, oxalic acid is always the most abundant diacid with a relative abundance higher than 60%. The climatology of C 2 -C 5 diacids in Europe is discussed versus environmental conditions at sites (marine/ continental, rural/forested, boundary layer/free troposphere, and winter/summer). Observations are used to discuss the possible sources of C 2 -C 5 diacids, with special emphasis on their primary versus secondary and natural versus anthropogenic origin. At surface sites in winter, fast secondary productions in wood burning plumes in addition to secondary production from volatile organic carbon (VOC) species emitted by vehicles seem to be important contributors. In summer the impact of anthropogenic sources is weakened and biogenic emissions from vegetation (unsaturated fatty acids, isoprene, oxygenated VOCs, and eventually monoterpenes) likely represent major precursors of diacids. At the Azores, diacids are not only related to long-range transport from continents but also to marine biogenic emissions from phytoplankton, particularly in summer.

Year‐round record of size‐segregated aerosol composition in central Antarctica (Concordia station): Implications for the degree of fractionation of sea‐salt particles

The origin of sea-salt aerosol that reaches the high Antarctic plateau and is trapped in snow and ice cores remains still unclear. In particular, the respective role of emissions from the open ocean versus those from the sea-ice surface is not yet quantified. To progress on this question, the composition of bulk and size-segregated aerosol was studied in 2006 at the Concordia station (75°S, 123°E) located on the high Antarctic plateau. A depletion of sulfate relative to sodium with respect to the seawater composition is observed on sea-salt aerosol reaching Concordia from April to September. That suggests that in winter, when the sea-salt atmospheric load reaches a maximum, emissions from the sea-ice surface significantly contribute to the sea-salt budget of inland Antarctica. Citation: Jourdain, B., S. Preunkert, O. Cerri, H. Castebrunet, R. Udisti, and M. Legrand (2008), Year-round record of size-segregated aerosol composition in central Antarctica (Concordia station): Implications for the degree of fractionation of sea-salt particles,

Sulfate trends in a Col du Dôme (French Alps) ice core: A record of anthropogenic sulfate levels in the European midtroposphere over the twentieth century

A high-resolution sulfate record from a Col du Dome (CDD, 4250 m above sea level, French Alps) ice core was used to investigate the impact of growing SO2 emissions on the midtroposphere sulfate levels over Europe since 1925. The large annual snow accumulation rate at the CDD site permits examination of the summer and winter sulfate trends separately. Being close to 80±10 ng g−1 in preindustrial summer ice, sulfate CDD summer levels then increase at a mean rate of 6 ng g−1 per year from 1925 to 1960. From 1960 to 1980 the increase continued at a rate of 24 ng g−1 per year. Concentrations reach a maximum of 860 ng g−1 in 1980 and subsequently decrease to 600 ng g−1 in the 1990s. These summer sulfate changes closely follow the course of growing SO2 emissions from source regions located within 700–1000 km around the Alps (France, Italy, Spain, and to a lesser extent, former West Germany). In winter the CDD sulfate levels are 3 to 8 times lower than in summer because of more limited upward transport of air masses from the boundary layer at that season. Being close to 20 ng g−1 in the preindustrial ice, winter levels were regularly enhanced at a mean annual rate of 1.2 ng g−1 from 1925 to 1980. The weak winter change from the preindustrial era to 1980 (a factor of 4 instead of 10 in summer) reflects a limited contamination of the free troposphere which, in contrast to summer, occurs at a larger scale (total Europe/former USSR). Intimately connected to Europe, these long-term changes in the Alps clearly differ in time and amplitude with the ones revealed by Greenland ice cores which indicate an increase by a factor of 3 between 1880 and 1970 in relation with long-range transport of pollutants from Eurasia as well as from North America. Furthermore, because of a lower natural contribution to the total sulfate level the anthropogenic changes can be more accurately derived in the Alps than in Greenland. Using the observed relationship between present-day concentrations in air and snowpack, the CDD ice core record permits reconstruction of present and past atmospheric sulfate concentrations at 4300 m above sea level over Europe in summer and winter. These data are compared with the sulfate levels simulated by current global sulfur models at 600 hPa for which uncertainties still range within a factor of 2. Together with observations made at lower elevation in the early 1990s the atmospheric levels derived for the CDD site (∼20 and 400 ng m−3 STP in winter and summer, respectively) document the vertical sulfate distribution between the ground and 4300 m elevation over western Europe at that time. In this way, data gained at high-elevation Alpine sites are powerful in evaluating the recent role of sulfate aerosol in forcing the climate over Europe.

Col du Dôme (Mt Blanc Massif, French Alps) suitability for ice‐core studies in relation with past atmospheric chemistry over Europe

The site of Col du Dôme glacier, located at 4250 m a.s.l. nearby the Mont Blanc summit (French Alps), was investigated for its suitability for reconstructing the anthropogenic perturbation of the atmosphere chemistry over Europe via glacio-chemical ice core studies. For this purpose, a 126 m long ice core drilled close to bedrock has been dedicated for glacio-chemical studies. Major ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl-,>NO3-, and SO42-) and D/H isotope ratios have been measured with high seasonal resolution along the upper 60 m of this core (covering 13 years). For dating by annual layer counting, a highly resolved ammonium profile was obtained for the entire core. To assess the spatial representativity of the chemical signals obtained from this core, additional chemical profiles were obtained from two shallow firn cores (13 and 20 m long) drilled at about 100 m from the deep ice core. All ice core parameters show regular seasonal variations with low winter and high summer values. Mean summer to winter ratios (averaged over the period 1981 to 1994) are close to 4 for NO3-, SO42- and Ca2+, but reach 14 for NH4+. While the shape of the mean seasonal cycles of NH4+, NO3-, and SO42- show a flat winter minimum followed by persistently high summer concentrations, more flickered variations are observed in the case of Ca2+. In contrast to the chemical species, δD shows a smoothed seasonal cycle. The chemical impurity levels and the δD content in snow deposits from Col du Dôme have been compared with those from Colle Gnifetti (4450 m a.s.l., located in the Swiss Alps, 80 km east of Col du Dôme) over a time period of 10 years. This comparison suggests that the two sites may experience similar atmospheric pollution conditions throughout the whole year, at least for NH4+, NO3-, and SO42-. Precise dating of the ice core drilled in 1994 was achieved by annual layer counting using the NH4+ stratigraphy. The latter reveals that the glacier of Col du Dôme records well preserved snow deposits, arising from summer as well as from winter precipitation, over, at least, the last 75 years. However, the seasonal signal of the δD content appears to be disturbed at increasing depth, in particular below of 115 m. A systematic decrease in the ratio of the winter to summer net snow accumulation found with increasing depth is shown to exert an important influence on mean temporal ice core trends for parameters underlying a strong seasonal variation. The comparison of chemical impurities between Col du Dôme and Colle Gnifetti indicates that glacio-chemical ice core records from Col du Dôme will provide seasonally resolved records over the 20th century which are at least representative on a regional scale.

Quantification of Dissolved Organic Carbon at Very Low Levels in Natural Ice Samples by a UV-Induced Oxidation Method

The study of chemical impurities trapped in solid precipitation and accumulated in polar ice sheets and high-elevation, midlatitude cold glaciers over the last several hundreds of years provides a unique way to reconstruct our changing atmosphere from the preindustrial era to the present day. Numerous ice core studies of inorganic species have already evaluated the effects of growing anthropogenic emissions of SO(2) or NO(x) on the chemical composition of the atmosphere in various regions of the world. While it was recently shown that organic species dominate the atmospheric aerosol mass, the contribution of anthropogenic emissions to their budget remains poorly understood. The study of organics in ice is at the infancy stage, and it still is difficult to draw a consistent picture of the organic content of polar ice from sparse available data. A UV oxidation method and IR quantification of CO(2) was optimized to obtain measurements of dissolved organic carbon content as low as a few ppbC. Stringent working conditions were defined to prevent contamination during the cleaning of ice. Measurements in various ice cores corresponding to preindustrial times revealed dissolved organic carbon content of less than 10 ppbC in Antarctica and up to 75 ppbC in alpine ice.

Causes of enhanced fluoride levels in Alpine ice cores over the last 75 years: Implications for the atmospheric fluoride budget

A continuous high-resolution record from a Col du Dome (Mont Blanc massif, 4250 m above sea level (asl), French Alps) ice core in addition to discontinuous samples from a Colle Gnifetti (Monte Rosa massif, 4450 m asl, Swiss Alps) ice core were used to reconstruct the history of the atmospheric fluoride pollution at the scale of Europe. Such studies are mandatory by large uncertainties in our understanding of the natural fluoride cycle which have confounded assessment of the environmental impact of anthropogenic emissions. For fluoride, advantages of Alpine ice core records with respect to the Greenland ones include less efficient post-depositional effects in relation with higher snow accumulation rates, and less contamination by quasi-permanent passive volcanic HF emissions at midlatitudes compared to the situation at high northern latitudes. Hence Alpine ice records permit detailed examination of natural sources of fluoride for the free troposphere over Europe and the impact of anthropogenic sources such as aluminium smelters, coal burning, and contribution of the stratospheric reservoir built up from the chlorofluorocarbon (CFC) degradation since the beginning of the twentieth century. At Col du Dome (CDD), fluoride concentrations in summer snow layers were close to 0.30 ng g -1 in 1930, started to increase in the late 1930s, reaching 1.4 ng g -1 in 1940 and 2.4 ng g -1 in the late 1960s. From 1970 to 1980 they were strongly decreased, exhibiting a plateau value close to 1.3 ng g -1 between 1980 and 1995. It is shown that at the scale of Europe in summer, soil dust emissions dominated the atmospheric fluoride budget prior to 1880. In the late 1960s the soil contribution decreased to 6 ± 1% due to enhanced release of fluoride by aluminium smelters and coal burning which accounted for 86 ± 3% and 8 ± 2% of the total fluoride content, respectively. From 1970 to 1980, effective precautions have been taken to minimize the release of fluoride from aluminium smelters to the atmosphere. Thus, over the 2 last decades, 26 ± 8% of the fluoride summer level of Alpine snow was due to coal combustion. The remaining part was related to the release from the less pollutant aluminium smelters as well as other anthropogenic processes (cement and phosphate industrial processings) (56 ± 11%) and to soil dust emissions (18 ± 2%). Winter levels close to 0.10 ng g -1 or less in 1930 were gradually increased after the late 1930s, reaching a maximum of 0.4 ng g -1 in 1970. Similarly to the summer level, the winter one has then strongly decreased (∼0.12 ng g -1 in 1980). A major difference between summer and winter trends is the reincrease of winter level up to 0.4 ng g -1 (i.e., similar to the 1970 maximum) in 1990. Such a very recent change of fluoride background levels may be partly related to the impact via stratosphere/troposphere exchanges of the growing HF stratospheric load related to the CFC degradation.

COLD, ALPINE ICE BODIES REVISITED: WHAT MAY WE LEARN FROM THEIR IMPURITY AND ISOTOPE CONTENT?

Abstract In the European Alps, ice core studies have been mainly performed in view of the recent man‐made influence on the atmospheric load of aerosol‐related species, while respective investigations on the pre‐industrial aerosol or on stable water isotope‐based climate records remained sparse. We address from a glaciological perspective the specific conditions of Alpine drilling sites and, in particular, the role of depositional noise. Thereby, we refer to two major drilling areas (located in the summit range of Monte Rosa and Mt Blanc massif, respectively) which largely differ in their snow accumulation rate and, hence, in their accessible time scale. A simple scheme considering the seasonality of both, the precipitation‐borne signal and the snow erosion‐controlled net accumulation rate is presented. It shows that water isotope trends are generally more sensitive to distortion by a seasonality effect than recent snow impurities trends, although the influence of a given seasonal accumulation rate cycle on the mean levels of water isotopes and impurities is similar. These findings are illustrated on the decadal and centennial time scale by the inter‐ and intra‐site variability of major ion and water isotope records. The intra‐site comparison includes the discussion of strong water isotope depletions seen some meters above bedrock at low accumulation drilling sites.

Asuma : un raid scientifique pour documenter la zone côtière de l'Antarctique

Le bilan de masse de surface des grandes calottes, c’est-à-dire le bilan comptable entre apports (précipitation, dépôt de neige par le vent, givre) et pertes (fonte, sublimation, érosion de la neige par le vent) de masse d’eau en surface des calottes, réagit en permanence aux variations du climat. Selon les estimations actuelles, l’augmentation de l’accumulation de neige en surface de l’Antarctique prévue pour la f in du XXIe siècle (15 % environ) représentera une compensation de l’élévation du niveau des mers d’environ 5 cm (voire 15 cm d’ici à 2200). Cette évolution prend en compte les conséquences de l’augmentation de l’humidité atmosphérique en réponse au réchauffement climatique, mais prend mal en considération les changements potentiels de circulation atmosphérique au-dessus de l’océan Austral et le long des côtes qui bordent l’Antarctique. Pourtant, en raison des variations attendues du gradient de pression entre moyennes et hautes latitudes, des déplacements du rail des dépressions sont prévus dans l’hémisphère Sud au cours du prochain siècle. C’est d’ailleurs déjà le cas, et des effets devraient déjà se faire sentir sur le bilan de masse de surface de l’Antarctique de l’Est. Certes, le bilan de masse de surface de cette partie du continent ne semble pas avoir connu de tendance notable au cours des dernières décennies, mais cette conclusion est facilement remise en doute en raison du manque de données de terrain de long terme, tout particulièrement dans la zone côtière de cette partie du continent. Le 1er décembre 2016, le raid scientif ique Asuma (improving the Accuracy of the Surface Mass balance of Antarctica) quittait la base de Cap Prud’homme en Antarctique, à quelques kilomètres de la base française de Dumont-d’Urville, en direction du centre du continent (figure 1). À bord de quatre tracteurs à chenilles et d’une dameuse, cinq scientifiques de l’Institut des géosciences de l’environnement (IGE) étaient épaulés par trois mécaniciens de l’Institut polaire PaulÉmile-Victor (Ipev) et un médecin. Pendant un peu plus d’un mois, ils ont parcouru 1 371 km sur la calotte polaire pour contribuer à améliorer la connaissance du continent antarctique et mieux évaluer les variations spatiotemporelles de son bilan de masse de surface et relier ces variations à d’éventuels changements de circulation dans la région.