Black carbon variability since preindustrial times in Eastern 1 part of Europe reconstructed from Mt Elbrus , Caucasus ice 2 cores 3

Black carbon (BC), emitted by fossil fuel combustion and biomass burning, is the second largest man13 made contributor to global warming after carbon dioxide (Bond et al., 2013). However, limited information 14 exists on its past emissions and atmospheric variability. In this study, we present the first high-resolution record 15 of refractory BC (rBC, including mass concentration and size) reconstructed from ice cores drilled at a high16 altitude Eastern European site in Mt. Elbrus (ELB), Caucasus (5115 m a.s.l.). The ELB ice core record, covering 17 the period 1825-2013, reflects the atmospheric load of rBC particles at the ELB site transported from the 18 European continent with a larger rBC input from sources located in the Eastern part of Europe. In the first half of 19 the 20 th century, European anthropogenic emissions resulted in a 1.5-fold increase in the ice core rBC mass 20 concentrations as respect to its level in the preindustrial era (before 1850). The rBC mass concentrations 21 increased by a 5-fold in 1960-1980, followed by a decrease until ~2000. Over the last decade, the rBC signal for 22 summer time slightly increased. We have compared the signal with the atmospheric BC load simulated using 23 past BC emissions (ACCMIP and MACCity inventories) and taken into account the contribution of different 24 geographical region to rBC distribution and deposition at the ELB site. Interestingly, the observed rBC 25 variability in the ELB ice core record since the 1960s is not in perfect agreement with the simulated atmospheric 26 BC load. Similar features between the ice core rBC record and the best scenarios for the atmospheric BC load 27 support that anthropogenic BC increase in the 20th century is reflected in the ELB ice core record. However, the 28 peak in BC mass concentration observed in ~1970 in the ice core is estimated to occur a decade later from past 29 inventories. BC emission inventories for the period 1960s-1970s may be underestimating European 30 anthropogenic emissions. Furthermore, for summer time snow layers of the last 2000s, the slightly increasing 31 trend of rBC deposition likely reflects recent changes in anthropogenic and biomass burning BC emissions in the 32 Eastern part of Europe. Our study highlights that the past changes in BC emissions of Eastern Europe need to be 33 considered in assessing on-going air quality regulation. 34

High resolution continuous rBC data recorded every second was smoothed at a depth resolution of 1 cm, except the upper section (surface to 7.2 m depth) of the 2009 core that was discretely analyzed at a depth resolution of ~5-10 cm.The density of rBC data points per year depends on annual snow accumulation rates and ice thinning with depth.The two ice cores are overlap for snow layers of year 2007-2009 (Fig. S1).The records described here for rBC concentrations are (i) the 2009 ice core from 2.9 m to 156.6 m, corresponding to calendar years of 1825-2008 and (ii) the top 15.9 m of the 2013 core, corresponding to calendar years of 2009-2013.These two ice core records cover the calendar years of 1825-2013.As a first survey for long-term rBC size distributions of ice core record, mass equivalent diameter of measured single rBC, D rBC , was calculated, assuming a void-free BC density of 1.8 g cm -3 (Moteki and Kondo, 2010).The calculated D rBC was in the range of ~70 and 620 nm.A series of test using mono-dispersed polystyrene latex (PSL) spheres with known diameters (150-600 nm) and poly-dispersed standard BC (Aquadag) suggests that the APEX-Q/SP2 system preserves original size information of rBC particles in liquid samples and provides highly reproducible rBC size measurements with a variation of < 5 nm (Sect.2.2.3 and 2.2.5 in Lim et al., 2014;Wendl et al., 2014).rBC size distributions were retrieved seasonally and simplified with a log-normal fit with a bin size (#)=200.Mass mode diameter (MMD) of the log-normal fit was then extracted to further reduce parameters.Size intervals between bin channels vary, with the minimum interval of less than 8 nm for the MMD 200-350 nm.Here, all SP2 data were processed with the SP2 toolkit developed by M. Gysel at the Paul Scherrer Institute (PSI, Switzerland; http://aerosolsoftware.web.psi.ch/).

Ice core dating and seasonal signature
Ice core dating was determined by counting annual layers from 1825 to 2013 using the seasonal cycles of ammonium, succinic acid and water stable isotopes (δD and δ 18 O) that were analyzed discretely.Based on the examination of the ammonium and succinic acid profiles, each annual layer was divided into two parts corresponding to snow deposition under winter condition and summer condition (Legrand et al., 2013;Preunkert et al., 2000).In addition, the annual layer counting was further confirmed using the reference horizon from a tritium peak (1963) and a volcanic horizon (Katmai in 1912).The mean annual net accumulation rate of 1455 mm w.e. for the last 140 years was estimated from these proxies.The dating uncertainty is likely on the order of a few years due to ice thinning with deeper depths.Further details about dating are found in Mikhalenko et al. (2015).
Ice core seasonality was determined by the ammonium stratigraphy and further verified by the isotope variations.
However, seasonal separation of the high-resolution rBC record made by lower-resolution ammonium profile was sometimes challenging particularly at the edge of two seasons, misleading winter (summer) rBC layers to be more concentrated (less concentrated) by the adjacent seasonal rBC layer.To avoid inaccurate separation of an annual ice layer into winter and summer intervals, only mid-summer and mid-winter rBC concentrations were extracted by considering data comprised between the 25 th percentile and the 75 th percentile of the depth thickness of each seasonal snow layer.The mid-summer and mid-winter are therefore corresponding roughly to the warmest three months and the coldest three months ("background winter") of a year.Later in the manuscript, summer and winter of this study will refer to mid-summer and mid-winter, respectively.

Model description and runs
FLEXPART v6.2 lagrangian particle dispersion model (LPDM) calculates the trajectories of tracer particles using the mean winds interpolated from the gridded analysis field and parameterizations representing turbulence and convective transport (Forster et al., 2007;Stohl and Thomson, 1999).FLEXPART was run using reanalysis fields of the European Centre for Medium-Range Weather Forecasts (ECMWF, ERA-Interim) at 0.75×0.75resolution, which is available since 1979.Here, a backward simulation mode was used to analyze particles transport pathways from potential flux regions to the sampling site (Seibert and Frank, 2004;Stohl et al., 2005).
To limit computational cost, simulations were performed for two selected periods: 2005-2009 and 1979-1983.We selected these periods because: (i) year 1979 is the first year of ECMWF data and year 2009 is the last year of our longer ice core (2009 ice core) that were analyzed prior to the 2013 ice core and (ii) these years are inflections in rBC trends (Sect.3.2).It would thus be sufficient to analyze transport patterns influencing rBC at ELB and determine potential changes in these transport patterns.1,000 particles are released at the drilling site during every 5-day interval in June to August (JJA) and in December to February (DJF).Modelled global average atmospheric lifetimes of BC particles varies by a factor of more than 3, ranging from 3 to 10 days (Bond et al., 2013).Because BC particles reaching the high-altitude ELB site would experience longer lifetimes than the particles transporting in the planetary boundary layer (PBL), simulations were performed using a BC lifetime of 5-, and 7-day.However, 7-day air mass trajectories were extending to the Pacific and therefore made little difference with the 5 days simulations.Thus we set the BC lifetime as 5-day.Number of particles were then computed every 3h at 0.5×0.5resolution.

Sensitivity by potential source regions
The finally defined footprint density F (i, j, n) is expressed as a parameter encompassing released particle number and residence time along the particles pathway, in procedure defined unit (p.d.u.).This final result is theoretically identical to potential emission sensitivity (PES), called source-receptor-relationship by Seibert and Frank (2004), which is proportional to the particle residence time in a particular grid cell with a fixed altitude range.
To facilitate analysis we reduced the number of variables from the gridded footprint density by summing them over large regions.We classified the footprint areas into five geographical regions with specific rBC emission sources (Figure 2).The regions identified are as follows: EEU (Eastern Europe including nearby the Mt.Elbrus, Ukraine and Europe Russia and a part of Middle East), CEU (Central Europe), WEU (Western Europe), NAF (North Africa), NAM (North America) and Others (The Atlantic and a part of Northern Europe above 60N).
To display our results, we first calculate the footprint density Fe of the entire footprint area: Here, F (i, j, n) is footprint density, where i and j are the indices of the latitude/longitude grid and n runs over the total number of cases N. Fe indicates the entire footprint area where the aerosols track during the last 5 days of transport.Note that we found little inter-annual variability in the footprint contribution of each region to the ELB site with a 3 % variation over the two periods (2005-2009 and 1979-1983) variability in footprint density is not large enough to influence on long-term rBC trends and the results over the two periods are thus fairly representative of 20 th century, we combined the simulations results and used this approach to study long-term emission contribution of each geographical region to rBC distribution and deposition at our drilling site.
In addition to the calculation using total particles in the atmospheric column, calculations using particles positioned in the lowest 2 km layers in the atmosphere were performed to investigate emission source regions of aerosols transporting from low altitudes.To show the potential particle transport strength of each region relative to the entire area, we calculated the percentages of the footprint density in each region relative to the one in the entire area.To do this, we sum Fe (i, j) over the entire footprint area resulting in one value.In the same way, we sum F (i, j) within each of the five regions resulting in five values.

Historic BC emission inventories
To describe temporal variability in the regional BC emissions and atmospheric load of BC transported to the ELB site, we used time-varying anthropogenic and biomass burning BC emissions estimated by ACCMIP (Emissions for Atmospheric Chemistry and Climate Model Intercomparison Project) inventory for the period 1900-2000 on the decadal scale (at 0. 5×0.5 resolution; Lamarque et al., 2010) and MACCity (MACC/CityZEN EU projects) inventory for the year 2008 (at 0. 5×0.5 resolution; Diehl et al., 2012;Granier et al., 2011;Lamarque et al., 2010;van der Werf et al., 2006).Note that the ACCMIP inventory provide decadal means (e.g., '1980' corresponds to the mean of 1980-1989) for the biomass burning estimates and representative values (e.g., '1980' is a representative of 1975-1985) for the anthropogenic estimates, leading to 5-year shift between two estimates.We used anthropogenic emission only for constraining BC emissions in DJF and both anthropogenic and biomass burning emissions for constraining BC emissions in JJA, because biomass burning frequently occurs in summer time as respect to anthropogenic emissions occurring year-round.

High resolution rBC record from Elbrus ice cores
We present the first high-resolution rBC record of ice cores drilled in the Mt.Elbrus, Caucasus (2009 and 2013 cores, Figure 3a).The rBC concentrations along the two cores ranged from 0.01 g L -1 to 222.2 g L -1 with a mean1 of 11.011.3g L -1 and a median of 7.2 g L -1 .A 20-m long section is zoomed in Figure 3b to highlight the higher resolution of rBC signals when continuously recorded at 1-cm depth interval compared to the surface snow and firn section (from top to 6.1 m) analyzed discretely at ~5-10 cm-depth interval.The rBC record was found to preserve sub-annual variability from top to depth of 156.6 m with rBC spikes reflecting large and abrupt variability in deposition of atmospheric rBC particles.Such high-resolution record brings new opportunities to study dynamic atmospheric vertical transport and/or sporadic events in a season.
A well-marked seasonal rBC cycle (e.g., Fig 3b) was characterized for the 2013 core and the 2009 core down to 156.6 m by consistent high summer values ranging from 0.2 to 222.2 g L -1 with a mean1 of 15.512.9g L -1 and a median of 11.7 g L -1 and low winter values ranging from 0.2 to 44.6 g L -1 with a mean1 of 5.95.1 g L -1 and a median of 4.5 g L -1 (Table 1).Peak rBC mass concentration of an annual snow layer was observed in summer snow layer.In atmospheric observations at ground-based sites in Western and Central Europe boundary layer, EC aerosol mass concentrations in winter are higher roughly by a factor of 2 than in summer mainly due to the enhanced domestic heating (Pio et al., 2007;Tsyro et al., 2007).In contrast to the boundary layer sites, the atmospheric measurements at high-elevation sites in Europe (e.g., Puy de Dôme at 1465 m a.s.l. and Sonnblick at 3106 m a.s.l.) revealed 2 to 3 times higher EC levels during summer than winter (Pio et al., 2007;Venzac et al., 2009), reflecting the efficient upward transport of BC aerosols from the polluted boundary layer to the high-altitudes during summer, primarily by thermally-driven convection and thickening boundarylayer height (Lugauer et al., 1998;Matthias and Bösenberg, 2002).This is consistent to the rBC seasonality observed in the ELB ice core.Concentrations and relative change to levels of preindustrial era (here, defined as 1825-1850) for given time periods are summarized in Table 1.For the period of 1825-1850, median ( standard deviation, SD) of rBC concentrations were 4.31.5 g L -1 in summer and 2.00.9 g L -1 in winter.The rBC concentrations increased by a ~1.5-fold in 1900-1950.Over the period of 1960-1980, rBC concentrations increased by a factor of 5.0 in summer and a factor of 3.3 in winter.The larger relative change of summer rBC than one of winter for the period suggests that rBC emissions in summer source region increased more sharply for this time period.Notably, in addition to medians, the lower 10 th percentiles of both summer and winter rBC increased since the preindustrial era, highlighting that rBC background level in the atmosphere at ELB was also significantly modified.

Long term evolution of rBC mass concentrations
Meanwhile, upper 10 th percentiles ranged up to 75 g L -1 and 35 g L -1 for summer and winter, respectively.
Of for the CDD core (a few data points for a decadal EC concentration).We thus focus on evaluating the ELB rBC record in Sect.3.5 by comparing with simulated atmospheric load of BC particles that were transported from source regions to the Mt.Elbrus.

Past variability in rBC size distributions
The first record of temporal and seasonal changes in rBC size distribution was extracted from the ELB ice core.
Mass equivalent diameter of rBC particles (D rBC ) was log-normally distributed.The mode of rBC mass size distributions (mass mode diameter, MMD) was determined for both summer and winter layers by fitting a lognormal curve to the measured distribution (e.g., Figure S2).This approach provides reliable results of representative rBC size in seasonal ice layers as the determined MMDs fall into the measured size range (~70-620 nm).Notably, rBC particles measured in this study show the MMD shifted to larger sizes than those measured in the atmosphere over Europe (MMD of 130-260 nm) (Dahlkötter et al., 2014;Laborde et al., 2013;Liu et al., 2010;McMeeking et al., 2010;Reddington et al., 2013), even larger than atmospheric rBC diameter measured at an high alpine site, Jungfraujoch (JFJ) in Switzerland (MMD of 220-240 nm) (Liu et al., 2010).The shift of rBC sizes induced by dry deposition should be negligible, as wet deposition with fairly constant precipitation throughout the year (e.g., 52% in summer and 48% in winter of annual mean precipitation at Pereval Klukhorskiy observatory located at 2037 m a.s.l. in the Western Caucasus) is the dominant aerosol removal pathway at this site (Mikhalenko et al., 2015).Similarly, significant snow melt was not observed in the ELB summer ice layers and post-deposition processes are thus not expected to alter rBC size distributions.Rather, the different rBC size distributions of the ice core from those in the atmosphere are likely associated with removal process of rBC particles during precipitation.Recent study using the SP2 technique showed the rBC size distribution in rainwater shifted to larger sizes (MMD= ~200 nm) than that in air (MMD= ~150 nm) in Tokyo, indicating that large rBC particles were more efficiently removed by precipitation (Mori et al., 2016).The preferential wet removal of larger rBC particles (Mori et al., 2016;Moteki et al., 2012) could reasonably explain the larger MMD of rBC particles observed in the ice core than atmospheric rBC aerosols (Schwarz et al., 2013).
The seasonal variations in rBC size distribution are clearly visible.In summer, the MMD varied ranging from 227.4 nm to 378.3 nm with a geometric mean of 290.81.1 nm (Fig. 5, red curve).In winter, the MMD varied ranging from 207.3 nm to 344.9 nm with a geometric mean of 268.71.1 nm (Fig. 5, blue curve).The rBC MMD of summer ice layers tended to be slightly larger than that of winter layers.Despite few observational evidences, we hypothesize that larger rBC size in summer may reflect advection of rBC aerosols transported from the PBL by thermally-driven convection, while in winter aerosols transported in the free troposphere (FT) could be smaller due to longer residence time in the atmosphere and accordingly, more chances for larger aerosols to be removed by precipitation prior to reaching the ELB site.Our hypothesis seems to be reasonable being consistent to the findings of in-situ aerosol measurements at high-altitude sites in Europe.Liu et al. (2010) found that rBC aerosols at JFJ were slightly larger when the site was influenced by valley sources, anthropogenic pollutants from lower altitudes.Submicron aerosol size distributions were also overall shifted to larger size in summer ( 50to 150 nm) than in winter (below 50 nm) at European mountain stations with altitude of ~1000-3000 m a.s.l.(Asmi et al., 2011).The authors in the latter explained this feature by relatively polluted air masses from the PBL during daytime in summer, but more influence of the FT air masses in winter.Similar to the clear seasonal cycle in rBC mass concentration, the clear seasonal rBC size distributions of the ELB ice core point out seasonal differences in origins of air masses reaching the ELB drilling site: PBL air with less chance of aerosol wet removal in summer and the free tropospheric air in winter.
In addition, the larger rBC MMD in summer layers can be associated with specific summer sources of atmospheric rBC particles, such as forest fires and/or agricultural fires.Particularly, forest fires in Southern Europe and agricultural fires in Eastern Europe may well contribute to summer aerosol loading in Europe (Bovchaliuk et al., 2013;van der Werf et al., 2010;Yoon et al., 2011).Previous SP2 studies have reported the larger size of rBC aerosols for biomass burning plumes, e.g., MMD of ~200 nm (Kondo et al., 2011b;Schwarz et al., 2008;Taylor et al., 2014) compared to rBC sizes for urban plumes.In the ELB ice core, we observed a maximum rBC MMD of 378.3 nm, with a maximum rBC mass concentration of 222.2 g L -1 in the late summer snow layer of year 2003, when extreme forest fire events occurred over the Iberian Peninsula and the Mediterranean coast (Barbosa et al., 2004;Hodzic et al., 2006) resulting from a record-breaking heatwave in Europe (Luterbacher et al., 2004;Schär et al., 2004).Both forward and backward air mass trajectories calculated from HYSPLIT model support that the ELB site was potentially influenced by the intense forest fires occurred in the Southern part of Europe on the mid-August 2003 (Fig. S3), when the top altitude of the PBL was estimated to be ~4.5 km high (Hodzic et al., 2006).Although speculative, this snow layer of year 2003 peaked with rBC concentration and enriched with larger-sizes rBC particles indicates potential contribution of biomass burning aerosols transported westerly to the ELB site.
The rBC size distributions preserved in Elbrus cores could be discussed as an influence of seasonal vertical transport versus emission sources of rBC aerosols and their wet removal properties.This rBC size information is potential to provide important implications particularly for the determination of snow-melting potential by rBC particles in snow (Flanner et al., 2007;Schwarz et al., 2013).Comparison of rBC size with well-established biomass burning proxies would be required to better characterize the dependency of rBC sizes with past fire activities.brings the greatest contribution with fairly consistent features for both seasons, accounting for 35.6 % and 30.9 % in JJA and DJF, respectively.A stronger seasonality was found in the region NAF and the region NAM, where the footprint contribution was larger in DJF by a 2-fold.This seasonal variation is caused by longer particle trajectories promoted by a faster zonal flow in winter across the North Atlantic from west to east.

Potential emission source regions
To investigate contributions of aerosols transporting from low altitudes which may reflect emissions at surface more sensitively, we calculated the footprint density of particles positioned in the lowest 2 km layers in the atmosphere.Note that we arbitrarily selected this vertical height of atmosphere (2 km layer) since particles positioned at lower atmosphere (e.g., ~1 km layer) was rarely observed in our simulations and the PBL heights were often higher in European mountains up to 3 km (Matthias, 2004).The results for JJA show that unlike in the entire atmospheric column, the contribution of footprint density from the region EEU was almost doubled in the 2 km layer, accounting for 63.6 % (Fig. 6c).Contrarily, in DJF, the proportion of the region EEU was only 22 % over total footprint density in this fixed layer.We thus infer that large seasonal increases observed during summer time in rBC mass concentration are likely driven by deposition of rBC aerosols transported from Eastern part of Europe and mostly originating from lower altitudes.
Therefore, these FLEXPART results confirm that rBC deposition to the Mt.Elbrus is most likely dominated by transport of BC emissions from the European continent, with the strongest BC inputs from the Eastern part of Europe particularly in summer.

New constrains on European BC emissions
Refractory BC concentrations of the ELB ice core increased rapidly from the 1950s to the 1980s (Figure 4 in Sect.3.2), and such trend record should primarily reflect changes in European BC emissions (Sect.3.4).Here, we compare past emission BC inventories with the ELB ice core record to bring new constrains on past European BC emissions.
Figure 8 shows temporal changes in anthropogenic and biomass burning BC emissions for the period 1900-2008 estimated by ACCMIP and MACCity (Diehl et al., 2012;Granier et al., 2011;Lamarque et al., 2010;van der Werf et al., 2006).The overall emission trends (black lines) illustrate a decrease of anthropogenic emissions since 1900 (Figure 8a) and a high variability of biomass burning emissions over the whole period (Figure 8b).
For anthropogenic emissions, the largest BC emissions in EEU and CEU regions occurred in 1980, followed by decreasing trends.WEU had the strongest BC emissions lasting until 1960, followed by a decrease of BC emissions lasting the present-day.In 2008, anthropogenic BC emissions in region EEU, CEU and WEU are comparable with an order of 0.2 Tg yr -1 .
To investigate factors controlling long-term rBC trends preserved in the ELB ice core, the temporal evolution of measured ice core rBC particles can be directly compared with that of atmospheric BC load at the ELB site, at least in relative manner.This comparison is provided in Fig. 9, in which ice core record is averaged along a decadal scale to be comparable with the historic BC emission data available on decadal scale only (Lamarque et al., 2010).Specifically, we coupled the BC emission intensities in each region and their relative contribution to the entire footprint area of ELB site (Figure 8c and d).The decadal BC emission burden in each region (Figure 8a and b) is therefore multiplied by the contribution of footprint density (Figure 7).Assumption behind this For summertime (JJA case, Fig. 9a) optimal agreement in trend pattern is observed between the ice core rBC and the atmospheric BC estimated in the lower 2 km layer with an increase at the onset of the 20 th century and a subsequent decrease since ~1980 ("best scenario").Specifically, substantial increase in atmospheric BC load is observed for the period 1910-1970, similar to the ELB rBC ice core record, only when the atmospheric BC considers BC particles transported in the lowest 2 km layer of the atmosphere.On the other side, the estimation derived from the entire atmospheric column does exhibit a different pattern.This comparison indicates that changes primarily in European anthropogenic BC emissions (e.g., industry, traffic and residential combustion), particularly ones of Eastern part of Europe, are consequently reflected in the ELB ice core rBC variability over the last century.
For wintertime (DJF case, Fig. 9b), the ice core rBC variability before 1980 can be explained by the atmospheric BC load (anthropogenic only) in the entire atmospheric column but without North American (NAM) contribution.With NAM contribution included in the simulation, the atmospheric BC is overestimated before 1980 resulting in a flat or a slightly downward trend for the period 1910-1970, unlike to the ice core rBC trend.
However, the good agreement between long-term rBC changes of Greenland ice core and modeled BC deposition in Greenland using a chemistry-climate model with an input of ACCMIP BC inventory confirm that BC emission estimates for NAM from the ACCMIP inventory correctly quantify anthropogenic BC emissions in North America (Lamarque et al., 2010).Consequently, the observed overestimation of NAM contribution for winter at the ELB site (Fig 9b) is likely due to an overestimation of NAM footprint density in the statistical process applied on FLEXPART simulation data.Finally, the estimated BC without NAM contribution is defined as the "best scenario" for winter time.
Despite the similar features between the ice core rBC record and the best scenario for the atmospheric load which support that anthropogenic BC increase in the 20 th century is reflected in the ELB record, BC maximum time period is not in total agreement (Fig. 9a and b).Unlike the ice core rBC that already largely increased in 1960 and peaked in 1970 for both summer and winter, the atmospheric BC load remarkably increases only in 1980.Substantial BC increase of ELB and Western European (CDD and CG) ice cores since the mid-20th century reveals that BC emissions increased during that period at a wide regional European scale.In addition, the CDD record shows a large increase in sulfate concentration since the mid-20th century lasting until ~1980 (Preunkert and Legrand, 2013;Preunkert et al., 2001).Knowing that sulfate and BC are often co-emitted in anthropogenic emission sources, e.g., in industrial sectors, one can expect a large increase in European BC emissions in 1960-1980, as suggested by the ELB ice core rBC record.The reliability of historic emission inventories for BC is reported to be lower than for SO 2 , CO and NOx emissions, particularly for the period prior to 2000 (Granier et al., 2011), which is due to the uncertainties on BC emission factors for coal, gasoline and diesel fuels in various sectors (differ by a factor of 10 or more in literatures) and activity data (Granier et al., 2011;Vignati et al., 2010).Thus, the lack of substantial increase in the atmospheric BC load for the period 1960s-1970s could be associated primarily with underestimated European anthropogenic BC emissions for this period (Fig. 8c and d).
Moreover, the ice core rBC record and the atmospheric BC load do not exhibit similar patterns after 1980.Decreasing rates of the ice core rBC are much slower after 1980 onward for both seasons than the atmospheric BC load (Fig. 9a and b).Furthermore, the summer rBC trend of the ELB ice core even increased since 2000, although such a trend cannot be reported conclusively for winter layers (Fig. 4).The recent economic growth in Eastern, and some part of Central, European countries (World Bank Group, 2016) can contribute to the enhancement in the release of BC and co-emitted pollutants.Some of Eastern European countries have kept increasing their sulfur emissions mainly from heat production and public electricity from 2000 onward (Vestreng et al., 2007).Thus, the increase in rBC deposition at the Elbrus site, mostly identified in summer, was probably related to enhanced emissions from anthropogenic sources located in Eastern and Central Europe.On the other side, many of Eastern European countries, such as Ukraine and European part Russia which are geographically close to the Mt.Elbrus, are the countries with the greatest land use for agriculture in Europe (Rabbinge and van Diepen, 2000), and thus emissions of smoke aerosols from their agricultural waste burning are expected to be significant in summer time (Barnaba et al., 2011;Bovchaliuk et al., 2013;Stohl et al., 2007).Large emissions of smoke aerosols over Eastern Europe from summer forest/agricultural fires have been recently reported (Barnaba et al., 2011;Bovchaliuk et al., 2013;Sciare et al., 2008;Yoon et al., 2011;Zhou et al., 2012) and burned area from Global Fire Emissions Database (GFED) (Giglio et al., 2010) increased over Eastern Europe for the period 2004-2008(Yoon et al., 2014)).These emissions of smoke aerosols in the Eastern part of Europe may have contributed to the observed summer BC increase in the ELB ice cores.Thus, the recent trend of the ELB ice core rBC turning upward probably indicates changes in both anthropogenic emissions and summer forest/peat fires over Eastern part of Europe in 2000s, which is not well reflected in the inventories.
Given the large existing uncertainties in historic BC emission inventories available to date, our rBC record reconstructed from a high-altitude Caucasus ice cores should be useful to better constrain BC emissions.
Specifically, our study highlights the need for improving BC emission inventories from the Eastern part of Europe since 1960.Reliability of Western European BC emissions could be more specifically assessed by investigating high-resolution BC records extracted from Western European ice cores that would be more representative of Western European emissions.

Conclusions
A high-resolution rBC record reconstructed from ice cores drilled from a high-altitude Eastern European site in Mt.Elbrus (ELB), Caucasus, reported for the first time the long-term evolutions of rBC mass concentrations and size distributions in the European outflows over the past 189 years, i.e., between year 1825 and year 2013.The rBC record at ELB is largely impacted by rBC emissions located in the Eastern part of Europe.A large temporal variability in rBC mass concentration was observed at both seasonal and annual timescales.This record is also unique to document long-term variability of BC in this region of Europe.
In the first-half of 20 th century, rBC concentrations increased by a 1.5-fold than its level in the preindustrial era (before 1850).The rBC concentrations increased by a 5-fold in 1960-1980, followed by a decrease until ~2000 and a slight increase again since ~2000.Consistent increase in background levels, since the beginning of 20 th century, highlights that rBC background level in the atmosphere at ELB was also significantly altered.We have also investigated the potential of size distributions of rBC particles in the ice cores as new a proxy to bring additional information on rBC removal processes, seasonal transport patterns, and emission sources.Information for each region is found in the Sect.2.4.and MACCity (Diehl et al., 2012;Granier et al., 2011;Lamarque et al., 2010;van der Werf et al., 2006).In (c) and (d), atmospheric BC load (Tg yr -1 ) is calculated by multiplying decadal-scale BC emissions in each region (a and b) by its relative contribution to the entire footprint area of ELB site (figure 7).In (c), both anthropogenic and biomass burning emissions are used for the reconstruction in JJA, as this type of biomass burning (forest fires and savanna burning) is the most frequent in summer and in (d), only anthropogenic emissions are used for DJF.Details are found in the text.
Time series of summer and winter medians of rBC mass concentrations from 1825 to 2013 are shown in Figure4.Medians are shown with lower and upper 10 th percentiles to illustrate seasonal rBC concentrations.The rBC concentrations varied significantly over the past ~190 years with a large inter-annual variability.Both summer and winter rBC medians increased gradually since the onset of 20 th century with a rapid increase in ~1950 lasting until ~1980.Median concentrations reached their maximums in the mid-1960s for summer (37.5 g L -1 ) and in the late 1970s for winter (14.7 g L -1 ).

Figure 5
Figure5shows time series of rBC MMD for the period of 1940 to 2009.The upper and lower limits of the periods selected for retrieving rBC MMD were chosen so as a large number of rBC particles in the seasonal ice layer would be available and would allow to secure reliable size distribution of the ice layer.Faster melting of snow layers of year 2010-2013 and thinner ice layers below the layer of year 1940 did not allow to record sufficient numbers of rBC particles and thus robust rBC size distributions could not be retrieve.For the considered time period, rBC MMD of both summer and winter layers varied ranging from 207.3 nm to 378.3 nm with a geometric mean of 279.41.1 nm.No clear temporal change in rBC MMD was identified over the 1940-2009 period.

Figure 6
Figure6illustrates potential source regions of BC aerosols reaching the ELB site.The model results show that relative to the footprints in JJA, footprints in DJF were more spread out of European continent and extended further over the Pacific (Figure6a and b).The relative contributions of each regional footprint density over the total density are summarized in Fig.7.Most of aerosols reaching the ELB site are transported from the European Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2016-804,2016   Manuscript under review for journal Atmos.Chem.Phys.Published: 16 September 2016 c Author(s) 2016.CC-BY 3.0 License.comparison is that (i) the atmospheric circulation and transport patterns do not change with time and (ii) that the mechanisms for BC depositing to snow remained constant.Hence, the proportionality between BC mass concentration in snow and atmospheric BC load has not varied with time.

Figure captions Figure 1 .
Figure captions Figure 1.Location of the ice core drilling site (43°20'53, 9"N, 42°25'36, 0"E, 5115 m a.s.l., indicated by the red star or arrow) in the Mt.Elbrus, the western Caucasus mountain range between the Black and the Caspian seas.

Figure 2 .
Figure 2. Five regions classified as potential rBC emission sources regions.

Figure 3 .
Figure 3.A Profile of high-resolution rBC concentration of Mt.Elbrus ice cores.(a) whole rBC profile of both the 2013 core and the 2009 core, and (b) the 2009 core from top to 20 m corresponding to the blue region in (a).In (b), lower resolution (at ~5-10 cm resolution; black color) and high resolution (at 1 cm resolution; red color) rBC profiles obtained from discrete analysis and continuous flow analysis, respectively, are shown.For a whole rBC record, a section of lower-resolution signals of the 2009 core (corresponding to calendar year 2009) was replaced with the high-resolution rBC signals of the 2013 core.Gray text on top of figures stands for calendar year corresponding to ice core depth.

Figure 4 .
Figure 4. Annually averaged temporal evolution in rBC mass concentration of the ELB ice cores.(a) Summer and (b) winter.Thin solid line is medians and dashed lines are lower and upper 10 th percentiles of the seasonal rBC values.Upper 10 th percentiles do not exceed 75 g L -1 and 35 g L -1 for mid-summer and mid-winter, respectively.Thick lines are 10-year smoothing of medians.Discontinuous thin lines indicate ice layers with unclear seasonality or unanalyzed ice layers.Note different y-scales for seasonal rBC concentrations.

Figure 5 .
Figure 5.Time series of mass mode diameter (MMD) of seasonal rBC size distributions for the period of 1940-2009.The MMD was obtained by fitting a log-normal curve to the measured distribution.Horizontal lines stand for geometric means for summer (red) and winter (blue).

Figure 6 .
Figure 6.Air mass footprint area for (a) June to August (JJA) and (b) December to February (DJF) in the atmospheric column and (c) JJA in the lowest 2 km in the atmosphere.Color bar on the left indicates footprints density with a process defined unit (p.d.u.).The location of the ELB site is marked by a white triangle.JJA and DJF correspond to summer and winter of the ELB ice core depth, respectively.

Figure 7 .
Figure 7. Contribution of each regional footprint density (%) for (a) JJA and (b) DJF in the atmospheric column and (c) JJA in the lowest 2 km in the atmosphere.Footprint density of each region is divided by the footprint density of the entire footprint area (EEU+CEU+WEU+NAF+NAM+Others) and then described in percentage.

Figure 8 .
Figure 8. Historic regional BC emissions and atmospheric BC load at ELB for the period 1900-2008.In (a) and (b), anthropogenic and biomass burning (forest fires and savanna burning) BC emissions estimated by ACCMIP

Figure 9 .
Figure 9.Comparison in temporal evolution between the rBC mass concentration of the ELB ice core and the estimates of atmospheric BC load at the ELB site, on a decadal scale.(a) JJA and (b) DJF.Best scenarios for atmospheric BC load are shown in black thick lines.In (b), NAM stands for North America.See the text and Figure 8c and d for calculations of the atmospheric BC load.
Jenk et al., 2006)07)bleThevenon et al., 2009)an mountain glaciers, only Col du Dôme (hereafter, CDD;Legrand et al., 2007)and ColleGnifetti (hereafter, CG;Thevenon et al., 2009)summer records provide EC records for the recent time(until ~1990 and 1980, respectively), whereas the Fiescherhorn (hereafter, FH;Jenk et al., 2006)record is available until 1940 only.Both summer records at CDD and CG show somewhat comparable preindustrial EC levels (~2 g L -1 for CDD and ~7 g L -1 for CG in the mid-1800s) to the ELB rBC (4.31.5 g L -1 in 1825-1850) and substantially increased EC concentrations for the period 1950-1980 since the mid-19 th century, similar to the ELB rBC.This suggests that EC emissions show a common trend at the European scale, and that such trend has been recorded in the different European high-altitude ice cores from CDD, CG, and ELB.
Some differences, such as peak time period and increase/decrease rate between records that may reflect subregional (e.g., Western Europe vs.Eastern Europe) emission changes, may be also noteworthy.However, direct comparison of the ELB rBC with the Western European ice core records should be made with caution owing to both (i) different analytical methods applied for the ice cores (e.g., ELB rBC: APEX-Q/SP2, CDD EC: thermaloptical method with EUSAAR2 protocol, and CG EC: thermal method) and (ii) lower data resolution particularlyAtmos.Chem.Phys.Discuss., doi:10.5194/acp-2016-804,2016Manuscriptunder review for journal Atmos.Chem.Phys.Published: 16 September 2016 c Author(s) 2016.CC-BY 3.0 License.