European CH 4 and N 2 O emissions are estimated for 2006 and 2007 using four inverse modelling systems, based on different global and regional Eulerian and La-grangian transport models. This ensemble ...approach is designed to provide more realistic estimates of the overall uncertainties in the derived emissions, which is particularly important for verifying bottom-up emission inventories. We use continuous observations from 10 European stations (including 5 tall towers) for CH 4 and 9 continuous stations for N 2 O, complemented by additional European and global discrete air sampling sites. The available observations mainly constrain CH 4 and N 2 O emissions from northwestern and eastern Europe. The inversions are strongly driven by the observations and the derived total emissions of larger countries show little dependence on the emission inventories used a priori. Three inverse models yield 26-56 % higher total CH 4 emissions from northwestern and eastern Europe compared Published by Copernicus Publications on behalf of the European Geosciences Union. 716 P. Bergamaschi et al.: Top-down estimates of European CH 4 and N 2 O emissions to bottom-up emissions reported to the UNFCCC, while one model is close to the UNFCCC values. In contrast, the inverse modelling estimates of European N 2 O emissions are in general close to the UNFCCC values, with the overall range from all models being much smaller than the UNFCCC uncertainty range for most countries. Our analysis suggests that the reported uncertainties for CH 4 emissions might be underestimated , while those for N 2 O emissions are likely overestimated .
During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO
2
) ...exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO
2
seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO
2
gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO
2
cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO
2
due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO
2
transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO
2
uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO
2
anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO
2
anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.
This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
This study aims to determine the mineral contribution to PM10 in the central Mediterranean Sea, based on 7 yr of daily PM10 samplings made on the island of Lampedusa (35.5° N, 12.6° E). The chemical ...composition of the PM10 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 PM10 sampling. The average PM10 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 PM10, 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 PM10 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 PM10 higher than 50 μg m−3, with dust contributing by 33% on average. The crustal contribution to PM10 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 PM10) 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 PM10 levels due to high background of natural aerosol. The crustal aerosol amount and contribution to PM10 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. Based 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 elements show somewhat higher values of Ca / Al and (Ca + Mg) / Fe (2.5 ± 1.0, and 4.7 ± 2.0, respectively) for Algeria–Tunisia than for Libyan origin (Ca / Al = 1.9 ± 0.7 and (Ca + Mg) / Fe = 3.3 ± 1.1).
We present an estimate of net ecosystem exchange (NEE) of CO₂ in Europe for the years 2001-2007. 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 -165 Tg C yr⁻¹ over the period considered. This uptake is predominantly in non-EU countries, and is found in the northern coniferous (-94 Tg C yr⁻¹) and mixed forests (-30 Tg C yr⁻¹) as well as the forest/field complexes of eastern Europe (-85 Tg C yr⁻¹). An optimistic uncertainty estimate derived using three biosphere models suggests the uptake to be in a range of -122 to -258 Tg C yr⁻¹, while a more conservative estimate derived from the a-posteriori covariance estimates is -165±437 Tg C yr⁻¹. 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 3 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.eu
Ground based measurements of aerosol optical depth, τ, and shortwave irradiance at the Mediterranean island of Lampedusa during 2003 and 2004 were used to estimate the surface aerosol shortwave ...radiative forcing. The shortwave forcing efficiency (FE) was derived at various solar zenith angles, θ, as the derivative of the shortwave irradiance with respect to τ. Values of FE for different classes of particles, namely desert dust, DD, biomass burning/industrial aerosols, BU, and for the whole dataset are derived. At the summer solstice the daily average FE is −86.4 W/m2 for DD, −70.5 W/m2 for BU, and −94.0 W/m2 for the whole dataset. The daily aerosol forcing of DD is much larger than for the other aerosol classes due to the combination of larger forcing efficiency and largest optical depths. The estimated average daily forcing at the summer solstice and equinox for DD is −30 and −24 W/m2, respectively.
Multi-filter rotating shadowband radiometer (MFRSR) measurements have been carried out at Lampedusa (35.52°N, 12.63°E) in 1999, and continuously since 2001. This study describes the Saharan dust (SD) ...events at Lampedusa on the basis of daily average optical depth at 500
nm,
τ, and Ångström exponent,
α, derived from these observations. Back-trajectories ending at Lampedusa at 2000 and 4000
m altitude were calculated by means of the HYSPLIT model. SD events are identified as those for which the trajectories interact with the mixed layer in places where the surface wind exceeds 7
m
s
−1, or spend a large fraction of time over the Sahara. The SD days display values of
α+Δ
α⩽1, with Δ
α equal to the standard deviation of the daily
α. Out of 911 days with cloud-free intervals, 233 (26%) are classified as SD, and correspond to 111 episodes of various duration, from 1 to 13 consecutive days. The occurrence of SD events is maximum in summer (33%), when also the largest seasonal average of
τ (0.40) is measured, and minimum in winter (7%), when the smallest seasonal average of
α (0.08) is found. SD days have been identified from the back-trajectories also in days lacking of observations, due to either cloudiness or measurement interruptions. The frequency of occurrence of SD days shows little change with respect to the cloud-free periods (24%). The seasonal distribution shows a peak in May (38%), followed by July (37%). Regions of SD production were derived from the HYSPLIT trajectories and NCEP-reanalysis surface winds. Finally, the MFRSR measurements at the solar zenith angle of 60° have been used to derive the single scattering albedo (SSA) for cases clearly dominated by dust (
τ⩾0.40 and
α+Δ
α⩽0.5). The average SSA for the whole period is 0.77±0.04 at 415.6
nm and 0.94±0.04 at 868.7
nm.
The Bayesian framework of CO2 flux inversions permits estimates of the retrieved flux uncertainties. Here, the reliability of these theoretical estimates is studied through a comparison against the ...misfits between the inverted fluxes and independent measurements of the CO2 Net Ecosystem Exchange (NEE) made by the eddy covariance technique at local (few hectares) scale. Regional inversions at 0.5° resolution are applied for the western European domain where ~ 50 eddy covariance sites are operated. These inversions are conducted for the period 2002–2007. They use a mesoscale atmospheric transport model, a prior estimate of the NEE from a terrestrial ecosystem model and rely on the variational assimilation of in situ continuous measurements of CO2 atmospheric mole fractions. Averaged over monthly periods and over the whole domain, the misfits are in good agreement with the theoretical uncertainties for prior and inverted NEE, and pass the chi-square test for the variance at the 30% and 5% significance levels respectively, despite the scale mismatch and the independence between the prior (respectively inverted) NEE and the flux measurements. The theoretical uncertainty reduction for the monthly NEE at the measurement sites is 53% while the inversion decreases the standard deviation of the misfits by 38%. These results build confidence in the NEE estimates at the European/monthly scales and in their theoretical uncertainty from the regional inverse modelling system. However, the uncertainties at the monthly (respectively annual) scale remain larger than the amplitude of the inter-annual variability of monthly (respectively annual) fluxes, so that this study does not engender confidence in the inter-annual variations. The uncertainties at the monthly scale are significantly smaller than the seasonal variations. The seasonal cycle of the inverted fluxes is thus reliable. In particular, the CO2 sink period over the European continent likely ends later than represented by the prior ecosystem model.
The coupling between oceanic and atmospheric sulfur cycles is fundamental for the understanding of the role of sulfate particles as potential climate regulators. We discuss existing relationships ...among methanesulfonate (MS− – one of the end products of oxidation of biogenic dimethylsulfide – DMS) in the atmospheric particulate, phytoplankton biomass, and remotely-sensed activity in the central Mediterranean. The MS− concentration in the aerosol particles is based on PM10 sampling (from 2005 to 2008) of atmospheric aerosols at the island of Lampedusa (35.5°N, 12.6°E) in the central Mediterranean Sea.
The marine primary production in the sea sector surrounding the sampling site is obtained by using Ocean Color remote sensed data (SeaWiFS, MODIS-Aqua). In particular, primary production is calculated using a bio-optical model of sea reflectance and a Wavelength-Depth-Resolved Model (WDRM), fed by elaborated satellite data (chlorophyll concentration in the euphotic layer – Chl, sea surface temperature) and daily solar surface irradiance measurements.
The multi-year evolution of MS− atmospheric concentration shows a well-defined seasonal cycle with a summer maximum, corresponding to the annual peak of solar radiation and a minimum of phytoplankton biomass (expressed as Chl).
Statistically significant linear relationships between monthly means of atmospheric MS− and both the phytoplankton productivity index PB (r2 = 0.84, p < 0.001) and the solar radiation dose (SRD; r2 = 0.87, p < 0.001) in the upper mixed layer of the sea around Lampedusa are found. These correlations are mainly driven by the common seasonal pattern and suggest that DMS production in the marine surface layer is mainly related to the phytoplankton physiology. High values of PB are also the expression of stressed cells. The main stress factors in Mediterranean Sea during summer are high irradiance and shallow depth of the upper mixed layer, which lead to enhanced DMS emissions and higher MS− amounts in the atmosphere.
During spring 2005 high biomass and primary productivity values are observed in February and April, just one month before the peaks of atmospheric MS− (March and May). The occurrence of anomalously high values at this time is hypothesized to be related to the negative phase of the North Atlantic Oscillation, and to related oceanic and atmospheric processes. The possible role of the taxonomic composition of phytoplankton assemblages is also discussed.
•Primary production is calculated for the sea around Lampedusa by bio-optical and WDRM models.•Significant relationship between atmospheric MS− and productivity index is found.•Significant relationship between atmospheric MS− and solar radiation dose is found.•MS− is related to the phytoplankton physiology, in turn related to variation of stress factors.•High MS− concentrations in spring 2005 could be related to NAO negative phase.
Saharan dust (SD) episodes occurring at the Mediterranean island of Lampedusa (35.52° N, 12.63° E) from May 1999 to December 2005 have been shown to occur in the 26% of the cloud-free days Meloni, ...D., di Sarra, A., Biavati, G., DeLuisi, J.J., Monteleone, F., Pace, G., Piacentino, S., Sferlazzo, D.M., 2007. Seasonal behavior of Saharan dust events at the Mediterranean island of Lampedusa in the period 1999–2005, Atmos. Environ. 41, 3041–3056. In this paper we focus on intense SD events detected until September 2006, characterized by large values of the Saharan Dust Event Index (SDEI), the sum of the daily average aerosol optical depth at 500 nm,
τ, over the duration of the dust episode. The SDEI index provides an indication about the intensity of SD events, due either to a long duration and/or to high dust optical depth. A total of 24 episodes characterized by large values of SDEI are examined. The NCEP-based maps of geopotential height and temperature at 700 mbar are used to identify the main circulation patterns driving SD to the Central Mediterranean and Lampedusa.
Dust transport episodes in summer last for several days, and the corresponding SDEI values are the highest of the year. These episodes are mainly governed by two circulation patterns: the trough extending near the Atlantic coast of Europe and the high pressure system present in North Africa, generally above 25° N. This configuration causes strong south-westerly flows from the Sahara towards Southern Italy. The time evolution of
τ for these long SD events shows that the largest values (>
0.3) are usually observed when the two patterns are present simultaneously, while low (<
0.3)
τ values are measured when the Atlantic trough influence is weak. Moreover, the most probable loading region typically shows a warm kernel in North-Western Sahara, with a tongue extending north-eastward towards Sicily.
In spring, moderate to high
τ are measured, and SD episodes last as long as 13 days. Two synoptic configurations can be distinguished. Days with large
τ are associated with the 700 mbar geopotential height features typical of summer. Days with moderate
τ are found to be characterized by the Saharan high, but with the close low replaced by the Atlantic trough descending West of Africa or above the Iberian peninsula.
In winter the typical meteorological conditions are determined by the presence of westerly cyclones. Depressions centered over Portugal, Central/Northern Europe, and Western Mediterranean have been shown to drive dust transport to Lampedusa.
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