The chemical characterization of PM2.5 was conducted at 5 rural background sites in France for the year 2013. Chemical analysis of daily samples every sixth day included the measurements of organic ...carbon (OC), elemental carbon (EC), ionic species and several specific primary and secondary organic tracers such as levoglucosan, polyols, methane sulfonic acid (MSA) and oxalate. The sampling sites were spatially distributed in order to be representative of the French atmospheric background. The results showed well identified temporal variations common to all the 5 sampling sites, covering a large fraction of France. During winter, concentrations of the biomass burning marker levoglucosan are significantly increased with high synchronous temporal pattern, indicating the strong impact of this source at a regional scale. During summer, concentrations of primary biogenic markers such as polyols (arabitol, mannitol) increase due to higher biological activities while oxalate contributions to OC also increases, attributed to ageing processes. The sources of primary organic aerosol are investigated using mono-tracer approaches based on these compounds. Results indicate that the relative contributions of wood burning to OC are very high, reaching an average value of 90% during winter for some of the rural sites. Terrestrial primary biogenic organic fraction is significant in summer and fall with a monthly contribution ranging from 4.5 to 9.5% of OC in PM2.5. A synchronous increase is also observed for secondary organic tracers (MSA, oxalic acid) during warm period confirming the influence on the large scale of these compounds that can account for 10–20% and 5–7% of the OC mass, respectively.
•Annual chemical composition and seasonal variability of rural PM2.5.•Synchronous variability of primary and secondary organic compounds.•OC source apportionment using primary molecular markers.•30% of the total OC attributed to the fungal spore during harvesting periods.•PSCF analysis highlighted a potential terrestrial additional source of MSA in continental sites.
Byline: S. Conil (1), H. Douville (1), S. Tyteca (1) Three ensembles of AMIP-type simulations using the Arpege-climat coupled land--atmosphere model have been designed to assess the relative ...influence of SST and soil moisture (SM) on climate variability and predictability. The study takes advantage of the GSWP2 land surface reanalysis covering the 1986--1995 period. The GSWP2 forcings have been used to derive a global SM climatology that is fully consistent with the model used in this study. One ensemble of ten simulations has been forced by climatological SST and the simulated SM is relaxed toward the GSWP2 reanalysis. Another ensemble has been forced by observed SST and SM is evolving freely. The last ensemble combines the observed SST forcing and the relaxation toward GSWP2. Two complementary aspects of the predictability have been explored, the potential predictability (analysis of variance) and the effective predictability (skill score). An analysis of variance has revealed the effects of the SST and SM boundary forcings on the variability and potential predictability of near-surface temperature, precipitation and surface evaporation. While in the tropics SST anomalies clearly maintain a potentially predictable variability throughout the annual cycle, in the mid-latitudes the SST forced variability is only dominant in winter and SM plays a leading role in summer. In a similar fashion, the annual cycle of the hindcast skill (evaluated as the anomalous correlation coefficient of the three ensemble means with respect to the "observations") indicates that the SST forcing is the dominant contributor over the tropical continents and in the winter mid-latitudes but that SM is supporting a significant part of the skill in the summer mid-latitudes. Focusing on boreal summer, we have then investigated different aspects of the SM and SST contribution to climate variations in terms of spatial distribution and time-evolution. Our experiments suggest that SM is potentially an additional source of climate predictability. A realistic initialization of SM and a proper representation of the land--atmosphere feedbacks seem necessary to improve state-of-the-art dynamical seasonal predictions, but will be actually efficient only in the areas where SM anomalies are themselves predictable at the monthly to seasonal timescale (since remote effects of SM are probably much more limited than SST teleconnections). Author Affiliation: (1) CNRM/GMGEC/UDC, Meteo France, 42 av. G. Coriolis, 31057 , Toulouse Cedex 1, France Article History: Registration Date: 22/06/2006 Received Date: 14/03/2006 Accepted Date: 15/06/2006 Online Date: 26/07/2006
We adapt general statistical methods to estimate the optimal error covariance matrices in a regional inversion system inferring methane surface emissions from atmospheric concentrations. Using a ...minimal set of physical hypotheses on the patterns of errors, we compute a guess of the error statistics that is optimal in regard to objective statistical criteria for the specific inversion system. With this very general approach applied to a real-data case, we recover sources of errors in the observations and in the prior state of the system that are consistent with expert knowledge while inferred from objective criteria and with affordable computation costs. By not assuming any specific error patterns, our results depict the variability and the inter-dependency of errors induced by complex factors such as the misrepresentation of the observations in the transport model or the inability of the model to reproduce well the situations of steep gradients of concentrations. Situations with probable significant biases (e.g., during the night when vertical mixing is ill-represented by the transport model) can also be diagnosed by our methods in order to point at necessary improvement in a model. By additionally analysing the sensitivity of the inversion to each observation, guidelines to enhance data selection in regional inversions are also proposed. We applied our method to a recent significant accidental methane release from an offshore platform in the North Sea and found methane fluxes of the same magnitude than what was officially declared.
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
) ...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
seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO
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
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
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
transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO
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
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
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'.
Seasonal climate forecasts mainly rely on the atmospheric sensitivity to its lower boundary conditions and on their own predictability. Besides sea surface temperature (SST), soil moisture (SM) may ...be an additional source of climate predictability particularly during boreal summer in the mid-latitudes. In this work, we investigate the role of SM initial conditions on near-surface climate predictability during ten boreal summer seasons using three complementary ensembles of AMIP-type simulations performed with the Arpège-Climat atmospheric general circulation model. First we have conducted an assessment of the SM predictability itself through a comparison of simple empirical SM models with Arpège-Climat. The statistical and dynamical models reveal similar SM prediction skill patterns but the Arpège-Climat reaches higher scores suggesting that it is at least suitable to explore the influence of SM initialization on atmospheric predictability. Then we evaluate the relationships between SM predictability and some near surface atmospheric predictability. While SM initialization obviously improves the predictability of land surface evaporation, it has no systematic influence on the precipitation and near surface temperature skills. Nevertheless, the summer hindcast skill is clearly improved during specific years and over certain regions (mainly north America and eastern Europe in the Arpège-Climat model), when and where the SM forcing is sufficiently widespread and strong. In this case, a significant impact is also found on the occurrence of heat waves and heavy rains, whose predictability at the seasonal timescale is a crucial challenge for years to come.
Besides sea surface temperature (SST), soil moisture (SM) exhibits a significant memory and is likely to contribute to atmospheric predictability at the seasonal timescale. In this respect, West ...Africa was recently highlighted as a “hot spot” where the land-atmosphere coupling could play an important role, through the recycling of precipitation and the modulation of the meridional gradient of moist static energy. Particularly intriguing is the observed relationship between summer monsoon rainfall over Sahel and the previous second rainy season over the Guinean Coast, suggesting the possibility of a soil moisture memory beyond the seasonal timescale. The present study is aimed at revisiting this question through a detailed analysis of the instrumental record and a set of numerical sensitivity experiments. Three ensembles of global atmospheric simulations have been designed to assess the relative influence of SST and SM boundary conditions on the West African monsoon predictability over the 1986-1995 period. On the one hand, the results indicate that SM contributes to rainfall predictability at the end and just after the rainy season over the Sahel, through a positive soil-precipitation feedback that is consistent with the “hot spot” hypothesis. On the other hand, SM memory decreases very rapidly during the dry season and does not contribute to the predictability of the all-summer monsoon rainfall. Though possibly model dependent, this conclusion is reinforced by the statistical analysis of the summer monsoon rainfall variability over the Sahel and its link with tropical SSTs. Our results indeed suggest that the apparent relationship with the previous second rainy season over the Guinean Coast is mainly an artefact of rainfall teleconnections with tropical modes of SST variability both at interannual and multi-decadal timescales.
In the course of the ICOS (Integrated Carbon Observation System) Demonstration Experiment a feasibility study on the usefulness of a travelling comparison instrument (TCI) was conducted in order to ...evaluate continuous atmospheric CO2 and CH4 measurements at two European stations. The aim of the TCI is to independently measure ambient air in parallel to the standard station instrumentation, thus providing a comprehensive comparison that includes the sample intake system, the instrument itself as well as its calibration and data evaluation. Observed differences between the TCI and a gas chromatographic system, which acted as a reference for the TCI, were -0.02 ± 0.08 μmol mol-1 for CO2 and -0.3 ± 2.3 nmol mol-1 for CH4 . Over a period of two weeks each, the continuous CO2 and CH4 measurements at two ICOS field stations, Cabauw (CBW), the Netherlands and Houdelaincourt (Observatoire Pérenne de l'Environnement, OPE), France, were compared to co-located TCI measurements. At Cabauw mean differences of 0.21 ± 0.06 μmol mol-1 for CO2 and 0.41 ± 0.50 nmol mol-1 for CH4 were found. For OPE the mean differences were 0.13 ± 0.07 μmol mol-1 for CO2 and 0.44 ± 0.36 nmol mol-1 for CH4 . Offsets arising from differences in the working standard calibrations or leakages/contaminations in the drying systems are too small to explain the observed differences. Hence the most likely causes of these observed differences are leakages or contaminations in the intake lines and/or their flushing pumps. For the Cabauw instrument an additional error contribution originates from insufficient flushing of standard gases. Although the TCI is an extensive quality control approach it cannot replace other quality control systems. Thus, a comprehensive quality management strategy for atmospheric monitoring networks is proposed as well.
Measuring the 14C / C depletion in atmospheric CO2 compared with a clean-air reference is the most direct way to estimate the recently added CO2 contribution from fossil fuel (ff) combustion (ΔffCO2) ...in ambient air. However, as 14CO2 measurements cannot be conducted continuously nor remotely, there are only very sparse 14C-based ΔffCO2 estimates available. Continuously measured tracers, like carbon monoxide (CO), that are co-emitted with ffCO2 can be used as proxies for ΔffCO2, provided that the ΔCO / ΔffCO2 ratios can be determined correctly (here, ΔCO refers to the CO excess compared with a clean-air reference). In the present study, we use almost 350 14CO2 measurements from flask samples collected between 2019 and 2020 at the urban site Heidelberg, Germany, and corresponding analyses from more than 50 afternoon flasks collected between September 2020 and March 2021 at the rural ICOS site Observatoire pérenne de l'environnement (OPE), France, to calculate average 14C-based ΔCO / ΔffCO2 ratios for those sites. For this, we constructed a clean-air reference from the 14CO2 and CO measurements of Mace Head, Ireland. By dividing the hourly ΔCO excess observations by the averaged flask ratio, we calculate continuous proxy-based ΔffCO2 records. The mean bias between the proxy-based ΔffCO2 and the direct 14C-based ΔffCO2 estimates from the flasks is – with 0.31 ± 3.94 ppm for the urban site Heidelberg and -0.06 ± 1.49 ppm for the rural site OPE – only ca. 3 % at both sites. The root-mean-square deviation (RMSD) between proxy-based ΔffCO2 and 14C-based ΔffCO2 is about 4 ppm for Heidelberg and 1.5 ppm for OPE. While this uncertainty can be explained by observational uncertainties alone at OPE, about half of the uncertainty is caused by the neglected variability in the ΔCO / ΔffCO2 ratios at Heidelberg. We further show that modeled ratios based on a bottom-up European emission inventory would lead to substantial biases in the ΔCO-based ΔffCO2 estimates for both Heidelberg and OPE. This highlights the need for an ongoing observational calibration and/or validation of inventory-based ratios if they are to be applied for large-scale ΔCO-based ΔffCO2 estimates, e.g., from satellites.
A 1000-year climate simulation is run with the ocean-atmosphere coupled model developed at the Institute Pierre-Simon Laplace (IPSL, Paris). No flux adjustment is used. The drift of the model is ...analyzed in terms of the seasurface temperature and deep ocean temperature. When the model's own equilibrium is reached, it is found that the Antarctic bottom water production experiences large-amplitude variation, oscillating between strong and weak episodes. This can yield oceanic temperature variation in the Southern Hemisphere and for the global mean.
Long-term monitoring at sites with relatively low particulate pollution could provide an opportunity to identify changes in pollutant concentration and potential effects of current air quality ...policies. In this study, 9-year sampling of PM10 (particles with an aerodynamic diameter below 10 µm) was performed in a rural background site in France (Observatoire Pérenne de l'Environnement or OPE) from 28 February 2012 to 22 December 2020. The positive matrix factorization (PMF) method was used to apportion sources of PM10 based on quantified chemical constituents and specific chemical tracers analysed on collected filters. Oxidative potential (OP), an emerging health metric that measures PM capability to potentially cause anti-oxidant imbalance in the lung, was also measured using two acellular assays: dithiothreitol (DTT) and ascorbic acid (AA). The sources of OP were also estimated using multiple linear regression (MLR) analysis. In terms of mass contribution, the dominant sources are secondary aerosols (nitrate- and sulfate-rich) associated with long-range transport (LRT). However, in terms of OP contributions, the main drivers are traffic, mineral dust, and biomass burning factors. There is also some OP contribution apportioned to the sulfate- and nitrate-rich sources influenced by processes and ageing during LRT that could have encouraged mixing with other anthropogenic sources. The study indicates much lower OP values than in urban areas. A substantial decrease (58 % reduction from the year 2012 to 2020) in the mass contributions from the traffic factor was found, even though this is not clearly reflected in its OP contribution. Nevertheless, the findings in this long-term study at the OPE site could indicate effectiveness of implemented emission control policies, as also seen in other long-term studies conducted in Europe, mainly for urban areas.
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