We present an estimate of net ecosystem exchange (NEE) of CO2 in Europe for the years 2001 through 2007. It is derived with a data assimilation that uses a large set of atmospheric CO2 mole fraction observations (<70 000) to guide relatively simple descriptions of terrestrial and oceanic net exchange, while fossil fuel and fire emissions are prescribed. Weekly terrestrial sources and sinks are optimized (i.e., a flux inversion) for a set of 18 large ecosystems across Europe in which prescribed climate, weather, and surface characteristics introduce finer scale gradients. We find that the terrestrial biosphere in Europe absorbed a net average of 2212165 TgC yr22121 over the period considered. This uptake is predominantly in non-EU countries, and is found in the northern coniferous (221294 TgC/yr) and mixed forests (221230 TgC yr22121) as well as the forest/field complexes of eastern Europe (221285 TgC yr22121). An optimistic uncertainty estimate derived using three biosphere models suggests the uptake to be in a range of 2212122 to 2212258 TgC yr22121, while a more conservative estimate derived from the a-posteriori covariance estimates is 2212165±437 TgC yr22121. Note however that uncertainties are hard to estimate given the nature of the system and are likely to be significantly larger than this. Interannual variability in NEE includes a reduction in uptake due to the 2003 drought followed by three years of more than average uptake. The largest anomaly of NEE occurred in 2005 concurrent with increased seasonal cycles of observed CO2. We speculate these changes to result from the strong negative phase of the North Atlantic Oscillation in 2005 that lead to favorable summer growth conditions, and altered horizontal and vertical mixing in the atmosphere. All our results are available through http://www.carbontracker.e
Abstract. Measurements of aerosol chemical composition made on the island of Lampedusa, south of the Sicily channel, during years [2004][2005][2006][2007][2008], are used to identify the influence of heavy fuel oil (HFO) combustion emissions on aerosol particles in the Central Mediterranean. Aerosol samples influenced by HFO are characterized by elevated Ni and V soluble fraction (about 80 % for aerosol from HFO combustion, versus about 40 % for crustal particles), high V and Ni to Si ratios, and values of V sol > 6 ng m −3 . Evidence of HFO combustion influence is found in 17 % of the daily samples. Back trajectories analysis on the selected events show that air masses prevalently come from the Sicily channel region, where an intense ship traffic occurs. This behavior suggests that single fixed sources like refineries are not the main responsible for the elevated V and Ni events, which are probably mainly due to ships emissions.V sol , Ni sol , and non-sea salt SO 2− 4 (nssSO 2− 4 ) show a marked seasonal behaviour, with an evident summer maximum. Such a pattern can be explained by several processes: (i) increased photochemical activity in summer, leading to a faster production of secondary aerosols, mainly nssSO 2− 4 , from the oxidation of SO 2 (ii) stronger marine boundary layer (MBL) stability in summer, leading to higher concentration of emitted compounds in the lowest atmospheric layers. A very intense event in spring 2008 was studied in detail, also using size segregated chemical measurements. These data show that elements arising from heavy oil combustion (V, Ni, Al, Fe) are distributed in the sub-micrometric fraction of the aerosol, and the metals are present as free metals, carbonates, oxides hydrates or labile complex with organic ligands, so that they are dissolved in mild condition (HNO 3 , pH1.5).Data suggest a characteristic nssSO 2− 4 /V ratio in the range 200-400 for HFO combustion aerosols in summer at Lampedusa. By using the value of 200 a lower limit for the HFO contribution to total sulphates is estimated. HFO combustion emissions account, as a summer average, at least for 1.2 µg m −3 , representing about 30 % of the total nssSO 2− 4 , 3.9 % of PM 10 , 8 % of PM 2.5 , and 11 % of PM1. Within the used dataset, sulphate from HFO combustion emissions reached the peak value of 6.1 µg m −3 on 26 June 2008, when it contributed by 47 % to nssSO 2− 4 , and by 15 % to PM 10 .
[1] Ground-based measurements of aerosol optical depth and surface shortwave irradiance carried out at the Mediterranean island of Lampedusa during 2004-2007 are used to estimate the surface aerosol direct radiative forcing for desert dust (DD), urban/ industrial-biomass burning (UI-BB), and mixed aerosols (MA). The aerosol single scattering albedo, w, at 415.6 and 868.7 nm is derived at 60°solar zenith angle, q, from measurements of global and diffuse radiation using radiative transfer model calculations. The shortwave forcing efficiency (FE S ) is derived, for q between 20°and 75°, for the three identified classes of aerosol and for all the observed data (AD The forcing efficiency of DD, UI-BB, and MA at q = 60°was calculated for three intervals of single scattering albedo (0.7 w < 0.8, 0.8 w < 0.9, 0.9 w 1) at 415.6 and 868.7 nm. The absolute value of FE S decreases with increasing w at 868.7 nm for all aerosol types, while it decreases with increasing w at 415.6 nm for UI-BB and MA and increases for DD. A 0.1 increment in the single scattering albedo at 868.7 nm produces a reduction in FE S by 25-30 W m À2 , and a reduction by 10-15 W m À2 in FE d .
Abstract. Previous studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than 1 year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA (Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie in French) have been deployed in the western Mediterranean region during 1 to 3 years depending on the station. The sites include, from south to north, Lampedusa, Majorca, Corsica, by satellites, more than 80 % of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different deposition sites in the Mediterranean studied area. The results tend to indicate that wet deposition is the main form of deposition for mineral dust in the western Mediterranean basin, but the contribution of dry deposition (in the sense that no precipitation was detected at the surface) is far from being negligible, and contributes 10 to 46 % to the major dust deposition events, depending on the sampling site.
Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters, and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 nm of 0.59) and by a low aerosol burden (5 May, with AOD of 0.14), are discussed. A radiative transfer model was initialized with the measured vertical profiles and with different aerosol properties, derived from measurements or from the literature. The simulation of the irradiance vertical profiles, in particular, provides the opportunity to constrain model-derived estimates of the AHR. The measured SW and LW irradiances were reproduced when the model was initialized with the measured aerosol size distributions and refractive indices. For the dust case, the instantaneous (solar zenith angle, SZA, of 55.1°) LW-to-SW ADRF ratio was 23% at the surface and 11% at the top of the atmosphere (TOA), with a more significant LW contribution on a daily basis (52% at the surface and 26% at TOA), indicating a relevant reduction of the SW radiative effects. The AHR profiles followed the aerosol extinction profile, with comparable peaks in the SW (0.72 ± 0.11 K d À1) and in the LW (À0.52 ± 0.12 K d À1) for the considered SZA. On a daily basis, the absolute value of the heating rate was larger in the LW than in the SW, producing a net cooling effect at specific levels. These are quite unexpected results, emphasizing the important role of LW radiation.
Abstract. This study aims to determine the mineral contribution to PM 10 in the central Mediterranean Sea, based on 7 yr of daily PM 10 samplings made on the island of Lampedusa (35.5 • N, 12.6 • E).The chemical composition of the PM 10 samples was determined by ion chromatography for the main ions, and, on selected samples, by particle-induced X-ray emission (PIXE) for the total content of crustal markers. Aerosol optical depth measurements were carried out in parallel to the PM 10 sampling.The average PM 10 concentration at Lampedusa over the period June 2004-December 2010 is 31.5 µg m −3 , with low interannual variability. The annual means are below the EU annual standard for PM 10 , but 9.9 % of the total number of daily data exceeds the daily threshold value established by the European Commission for PM (50 µg m −3 , European Community, EC/30/1999).The Saharan dust contribution to PM 10 was derived by calculating the contribution of Al, Si, Fe, Ti, non-sea-salt (nss) Ca, nssNa, and nssK oxides in samples in which PIXE data were available. Cases in which crustal content exceeded the 75th percentile of the crustal oxide content distribution were identified as elevated dust events. Using this threshold, we obtained 175 events. Fifty-five elevated dust events (31.6 %) displayed PM 10 higher than 50 µg m −3 , with dust contributing by 33 % on average.The crustal contribution to PM 10 has an annual average value of 5.42 µg m −3 , and reaches a value as high as 67.9 µg m −3 (corresponding to 49 % of PM 10 ) during an intense Saharan dust event.The crustal content estimated from a single tracer, such as Al or Ca, is in good agreement with the one calculated as the sum of the metal oxides. Conversely, larger crustal contents are derived by applying the EU guidelines for demonstration and subtraction of exceedances in PM 10 levels due to high background of natural aerosol. The crustal aerosol amount and contribution to PM 10 showed a very small seasonal dependence; conversely, the dust columnar burden displays an evident annual cycle, with a strong summer maximum (monthly average aerosol optical depth at 500 nm up to 0.28 in June-August). We found that 71.3 % of the dust events identified from optical properties over the atmospheric column display a high dust content at the ground level. Conversely, the remaining 28.7 % of cases present a negligible or small impact on the surface aerosol composition due to the transport processes over the Mediterranean Sea, where dust frequently travels above the marine boundary layer, especially in summer.Published by Copernicus Publications on behalf of the European Geosciences Union. M. Marconi et al.: Saharan dust aerosol over the central Mediterranean SeaBased on backward trajectories, two regions, one in Algeria-Tunisia, and one in Libya, are identified as main source areas for intense dust episodes occurring mainly in autumn and winter. Data on the bulk composition of mineral aerosol arising from these two source areas are scarce; results on characteristic ratios between ele...
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