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Atmospheric iron (Fe) deposition to the open ocean affects net primary productivity, nitrogen fixation, and carbon uptake. We investigate changes in soluble Fe (SFe) deposition from the pre-industrial period to the late 21st century using the EC-Earth3-Iron Earth System model. EC-Earth3-Iron considers various sources of Fe, including dust, fossil fuel combustion, and biomass burning, and features comprehensive atmospheric chemistry, representing atmospheric oxalate, sulfate, and Fe cycles. We show that anthropogenic activity has changed the magnitude and spatial distribution of SFe deposition by increasing combustion Fe emissions and atmospheric acidity and oxalate levels. We report that SFe deposition has doubled since the early industrial era, using the Coupled Model Intercomparison Project Phase 6 emission inventory. We highlight acidity as the main solubilization pathway for dust-Fe and oxalate-promoted processing for the solubilization of combustion-Fe. We project a global SFe deposition increase of 40% by the late 21st century relative to present day under Shared Socioeconomic Pathway (SSP) 3–7.0, which assumes weak climate change mitigation policies. Conversely, SSPs with stronger mitigation pathways (1–2.6 and 2–4.5) result in 35% and 10% global decreases, respectively. Despite these differences, SFe deposition increases over the equatorial Pacific and decreases in the Southern Ocean (SO) for all SSPs. We further observe that deposition over the equatorial Pacific and SO are highly sensitive to future changes in dust emissions from Australia and South America, as well as from North Africa. Future studies should focus on the potential impact of climate- and human-induced changes in dust and wildfires combined. This work was funded by the European Research Council under the Horizon 2020 research and innovation programme through the ERC Consolidator Grant FRAGMENT (grant agreement no. 773051), the AXA Research Fund through the AXA Chair on Sand and Dust Storms at BSC, the Spanish Ministerio de Economía y Competitividad through the NUTRIENT project (CGL2017-88911-R), the European Union's Horizon 2020 research and innovation programme under grant agreement no 821205 (FORCeS), and ESA through the DOMOS project (ESA AO/1-10546/20/I-NB). We acknowledge the EMIT project, which is supported by the National Aeronautics and Space Administration Earth Venture Instrument program, under the Earth Science Division of the Science Mission Directorate. RLM received additional support from the NASA Modeling, Analysis and Prediction Program (NNG14HH42I). We also acknowledge the resources obtained on the Marenostrum4 supercomputer at BSC, granted through the PRACE project eFRAGMENT2 and RES project AECT-2020-3-0020, along with the technical support provided by BSC and the Computational Earth Sciences team of the BSC Earth Sciences Department.

Clouds are large contributors to uncertainty in climate projections, with aerosol-cloud interactions playing a key role. To better reproduce heterogeneous ice clouds and, ultimately, the Earth’s changing energy budget in EC-Earth3 (one of the CMIP6 Earth System Models), its heterogeneous ice nucleation scheme has been updated. Specifically, the temperature-based parameterization has been substituted by a combination of aerosol-and-temperature-sensitive ice nucleating parameterizations. In particular, the model now considers a dust-and-soot-sensitive deposition nucleation scheme for cirrus clouds and aerosol-sensitive immersion freezing schemes for mixed-phase clouds. The latter is sensitive to the mineralogical composition of dust, specifically to the content of K-feldspar and quartz, and to marine organic aerosols, which are explicitly traced in EC-Earth3. Moreover, a secondary ice production parameterization based on a random forest regressor enhances the ice formed by the primary processes.We evaluate the model against an extended observational dataset of INP concentrations and analyze the effect of modelled aerosols upon heterogeneous ice nucleation in mixed-phase clouds and cirrus clouds produced with the new parameterizations. We also investigate the sensitivity of the simulated liquid and ice water content and the atmospheric radiative fluxes to the two different soil mineralogy atlases. Additionally, we use this updated model version to study in more detail a severe dust intrusion event that produced dust-infused clouds that affected Europe in March 2022.The results with the new ice nucleation parameterizations show a clear association of the simulated ice crystal number concentrations with the aerosol sources and transported regions. We also show that replacing the temperature-dependent ice nucleation parameterization with an aerosol-sensitive parameterization in EC-Earth3 significantly impacts surface temperature at high latitudes.

In high-latitude regions, larger and more frequent fires have been occurring over recent years, a tendency that is expected to continue in the coming decades due to warmer temperatures and regionally decreased precipitation imposed by climate change (IPCC,2019). Boreal wildfires in general are a significant source of CO2 emissions, as well as other greenhouse gases and aerosols (Akagi et al. 2011; Van Der Werf et al. 2010), e.g. emissions from boreal forests between 1997 and 2016 accounted for 7.4% of the global emissions (van der Werf et al. 2017). The effects of boreal fires on future climate have not been investigated and are potentially of great importance since climate change is occurring more rapidly in those high-latitude areas. More flammable forests in addition to the large carbon-rich peatlands, will potentially lead to devastating consequences.The overall goal of our project is to quantify the effects of high-latitude wildfire emissions on atmospheric composition as well as climate. For this purpose, simulations with the EC Earth Earth System Model (ESM) are being employed to characterize the past, present and future variability and changes of wildfires especially in high latitudes. In the results presented here, we demonstrate how the EC Earth model performs when forced with prescribed fire emissions (GFED4) and with a more detailed peat fire module developed by our team. The mean state, seasonality, and interannual variability of fire emissions and key atmospheric constituent abundances (black carbon, organic carbon, NOx, CO, ozone, amongst others) are validated in the model, using a range of observational datasets. This validation exercise is a key step before employing the EC-Earth model for quantifying future impacts of high-latitude fires on atmospheric composition and climate. IPCC,2019: Jia, G., E. Shevliakova, P. Artaxo, N. De Noblet-Ducoudré, R. Houghton, J. House, K. Kitajima, C. Lennard, A. Popp, A. Sirin, R. Sukumar, L. Verchot, 2019: Land–climate interactions. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems [P.R. Shukla, J. Skea, E. Calvo Buendia, V. Masson-Delmotte, H.-O. Pörtner, D.C. Roberts, P. Zhai, R. Slade, S. Connors, R. van Diemen, M. Ferrat, E. Haughey, S. Luz, S. Neogi, M. Pathak, J. Petzold, J. Portugal Pereira, P. Vyas, E. Huntley, K. Kissick, M, Belkacemi, J. Malley, (eds.)]. In press.Akagi, S.K. et al., 2011: Emission factors for open and domestic biomass burning for use in atmospheric models. Atmos. Chem. Phys., 11, 4039–4072, doi:10.5194/acp-11-4039-2011.Van Der Werf, G.R. et al., 2010: Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009). Atmos. Chem. Phys., 10, 11707–11735, doi:10.5194/acp-10-11707-2010.Van Der Werf, G.R. et al., 2010: Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009). Atmos. Chem. Phys., 10, 11707–11735, doi:10.5194/acp-10-11707-2010.

The ocean plays a key role in climate change mitigation by absorbing heat and CO2 accumulating in the atmosphere due to anthropogenic greenhouse gases emissions. While it is commonly accepted that anthropogenic CO2 is absorbed by the ocean primarily through physical and chemical mechanisms, biological cycling of carbon is mainly responsible for maintaining the vertical gradient of dissolved inorganic carbon in the ocean. Thanks to a series of processes known as the biological carbon pump, oceanic phytoplankton uptakes carbon and promotes sinking of particulate organic matter to the deeper ocean. Uncertainty about the strength of these processes and about their response to ongoing and projected climate change is large enough to confound predictions of future ocean carbon uptake. One of the most important limiting factors for phytoplankton growth over large oceanic areas is the availability of iron. While there is no doubt regarding the importance of dust transport and deposition over open oceans as the most important iron source, questions remain still open regarding closing the relationship between dust sources, long-range transport, iron solubilisation during transport and deposition processes. Overall, better understanding the mechanisms behind the spatial and temporal variability of atmospheric dust-ocean interactions is key to interpret the response of ocean biogeochemistry and to increase confidence in future climate projections. In this work, we present a reconstruction of global ocean biogeochemistry for the last 30 years, where we evaluate the impact on ocean biogeochemical cycles of newly produced iron deposition fields. These were derived with EC-Earth3-Iron, a version of the Earth System Model EC-Earth3 with a state-of-the-art description of the atmospheric iron cycle. EC-Earth3-Iron estimates iron emissions considering explicitly the mineralogy of dust sources, and accounts for the contribution of anthropogenic combustion and biomass burning sources. The model includes an advanced representation of the iron solubilization in the atmosphere, which occurs through acidic attack, organic-ligand mediated dissolution and photo-reductive processes. Furthermore, it allows distinguishing the contribution to the soluble (and total) iron deposition in the ocean of the natural and anthropogenic dust sources, fossil fuels combustion and biomass burning, and characterizing thus separately their impact on ocean biogeochemistry. We compare the ocean biogeochemistry reconstruction against a control where commonly used climatologies for iron deposition fields are prescribed.

Ice-nucleating particles (INPs) enable ice formation, profoundly affecting the microphysical and radiative properties, lifetimes, and precipitation rates of clouds. Mineral dust emitted from arid regions, particularly potassium-containing feldspar (K-feldspar), has been shown to be a very effective INP through immersion freezing in mixed-phase clouds. However, despite the fact that quartz has a significantly lower ice nucleation activity, it is more abundant than K-feldspar in atmospheric desert dust and therefore may be a significant source of INPs. In this contribution, we test this hypothesis by investigating the global and regional importance of quartz as a contributor to INPs in the atmosphere relative to K-feldspar. We have extended a global 3-D chemistry transport model (TM4-ECPL) to predict INP concentrations from both K-feldspar and quartz mineral dust particles with state-of-the-art parameterizations using the ice-active surface-site approach for immersion freezing. Our results show that, although K-feldspar remains the most important contributor to INP concentrations globally, affecting mid-level mixed-phase clouds, the contribution of quartz can also be significant. Quartz dominates the lowest and the highest altitudes of dust-derived INPs, affecting mainly low-level and high-level mixed-phase clouds. The consideration of quartz INPs also improves the comparison between simulations and observations at low temperatures. Our simulated INP concentrations predict ~¿51¿% of the observations gathered from different campaigns within 1 order of magnitude and ~¿69¿% within 1.5 orders of magnitude, despite the omission of other potentially important INP aerosol precursors like marine bioaerosols. Our findings support the inclusion of quartz in addition to K-feldspar as an INP in climate models and highlight the need for further constraining their abundance in arid soil surfaces along with their abundance, size distribution, and mixing state in the emitted dust atmospheric particles. This work has been supported by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (PANACEA; MIS 5021516), which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). Nikos Daskalakis, Maria Kanakidou, Mihalis Vrekousis acknowledge support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy (University Allowance, EXC 2077, University of Bremen). Maria Kanakidou, Marios Chatziparaschos, Athanasios Nenes, Montserrat CostaSurós, María Gonçalves Ageitos, and Carlos Pérez García-Pando acknowledge support by the European Union Horizon 2020 project FORCeS under grant agreement no. 821205. Carlos Pérez GarcíaPando, Montserrat Costa-Surós, and María Gonçalves Ageitos acknowledge support from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant no. 773051; FRAGMENT) and from the AXA Research Fund. Montserrat Costa-Surós has received funding from the European Union’s Horizon 2020 research and innovation programme, under the Marie Skłodowska-Curie grant agreements, grant no. 754433, from the call H2020-MSCA-COFUND-2016. We thank Joseph M. Prospero for PM10 measurements in Banizoumbou (Niger), Cinzana (Mali), M’Bour (Senegal), which were performed in the framework of the French National Observatory Service INDAAF (International Network to study Deposition and Atmospheric composition in Africa; https://indaaf.obs-mip.fr/, last access: 27 January 2021), piloted by the LISA and LAERO and supported by the INSU/CNRS, the IRD, and the Observatoire MidiPyrénées and the Observatoire des Sciences de l’Univers EFLUVE and Michael Pikridas from the Climate and Atmosphere Research Center of The Cyprus Institute. This research has been supported by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020) and co-financed by Greece and the European Regional Development Fund (grant no. MIS 5021516) and EU-Horizon 2020 project FORCeS (grant no. 821205). Peer Reviewed Objectius de Desenvolupament Sostenible::13 - Acció per al Clima

The atmospheric budget of carbonyl sulfide (COS, lifetime ~2 years) is primarily determined by emissions from anthropogenic and oceanic sources and uptake by the biosphere. Once the budget of COS is adequately understood, COS could be a suitable tracer to estimate Gross Primary Productivity (GPP), since stomatal uptake by plants is basically a one-way process, unlike the assimilation of CO2. However, currently the global budget of COS is not closed. Here, we will report progress on the use of inverse modelling to better constrain the atmospheric COS budget. To that end, we assimilate data from the MIPAS instrument that flew onboard the ENVISAT satellite (2002–2012). MIPAS is a limb sounder that measures atmospheric emission profiles down to the upper troposphere. Tropospheric COS retrievals are assimilated together with NOAA COS surface observations, and a bias correction scheme is employed to correct for potential calibration differences. Using the 4DVAR-TM5 model, we derive a consistent global COS budget. However, evaluation with independent data reveals that TM5 remains biased low in the free troposphere. We will show that this underestimate may be resolved by accounting for an aqueous-phase oxidation process of the newly discovered HydroPeroxyMethylThioFormate (HPMTF) intermediate in the DMS oxidation chain.

Atmospheric Ice nuclei particles regulate in cloud properties such as, cloud lifetime, precipitation rates and cloud’s radiative properties due to their ability to trigger ice heterogenous formation. Particles ejected into the atmosphere during bubble bursting through the sea surface microlayer, which is enriched in organic matter, are considered as the major precursors of INPs over the ocean. In addition, mineral dust particles that are considered as the most important precursor of INP in the mixed-phase cloud regime globally and terrestrial bioaerosols that have been also shown to have INP activity are transported over the ocean and contribute to the INP in the marine environment.In the present study we present results from the global 3-D chemistry transport model TM4-ECPL that accounts for INPs concentrations from marine organic aerosols, terrestrial bioaerosol and K-rich feldspar and quartz mineral dust particles. The simulated distribution of INP concentrations over the global ocean agrees with currently available ambient measurements. The relative contribution of the various INP precursors in the different compartments of the marine atmosphere is discussed on the basis of simulated 3-dimensional number concentrations of INP, providing insight to the cloud glaciation processes in the marine environment.Support from PANACEA (MIS 5021516) funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund), and the Excellence grant, the U Bremen Excellence Chair and the European Union Horizon 2020 project FORCeS under grant agreement No 821205.

International audience; A key Earth system science question is the role of atmospheric deposition in supplying vital nutrients to the phytoplankton that form the base of marine food webs. Industrial and vehicular pollution, wildfires, volcanoes, biogenic debris, and desert dust all carry nutrients within their plumes throughout the globe. In remote ocean ecosystems, aerosol deposition represents an essential new source of nutrients for primary production. The large spatiotemporal variability in aerosols from myriad sources combined with the differential responses of marine biota to changing fluxes makes it crucially important to understand where, when, and how much nutrients from the atmosphere enter marine ecosystems. This review brings together existing literature, experimental evidence of impacts, and new atmospheric nutrient observations that can be compared with atmospheric and ocean biogeochemistry modeling. We evaluate the contribution and spatiotemporal variability of nutrient-bearing aerosols from desert dust, wildfire, volcanic, and anthropogenic sources, including the organic component, deposition fluxes, and oceanic impacts. Expected final online publication date for the Annual Review of Marine Science, Volume 14 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Understanding how multiphase processes affect the iron-containing aerosol cycle is key to predict ocean biogeochemistry changes and hence the feedback effects on climate. For this work, the EC-Earth Earth system model in its climate-chemistry configuration is used to simulate the global atmospheric oxalate (OXL), sulfate (SO42−), and iron (Fe) cycles, after incorporating a comprehensive representation of the multiphase chemistry in cloud droplets and aerosol water. The model considers a detailed gas-phase chemistry scheme, all major aerosol components, and the partitioning of gases in aerosol and atmospheric water phases. The dissolution of Fe-containing aerosols accounts kinetically for the solution’s acidity, oxalic acid, and irradiation. Aerosol acidity is explicitly calculated in the model, both for accumulation and coarse modes, accounting for thermodynamic processes involving inorganic and crustal species from sea salt and dust. Simulations for present-day conditions (2000–2014) have been carried out with both EC-Earth and the atmospheric composition component of the model in standalone mode driven by meteorological fields from ECMWF’s ERA-Interim reanalysis. The calculated global budgets are presented and the links between the 1) aqueous-phase processes, 2) aerosol dissolution, and 3) atmospheric composition, are demonstrated and quantified. The model results are supported by comparison to available observations. We obtain an average global OXL net chemical production of 12.61 ± 0.06 Tg yr−1 in EC-Earth, with glyoxal being by far the most important precursor of oxalic acid. In comparison to the ERA-Interim simulation, differences in atmospheric dynamics as well as the simulated weaker oxidizing capacity in EC-Earth result overall in a ~30 % lower OXL source. On the other hand, the more explicit representation of the aqueous-phase chemistry in EC-Earth compared to the previous versions of the model leads to an overall ~20 % higher sulfate production, but still well correlated with atmospheric observations. The total Fe dissolution rate in EC-Earth is calculated at 0.806 ± 0.014 Tg Fe yr−1 and is added to the primary dissolved Fe (DFe) sources from dust and combustion aerosols in the model (0.072 ± 0.001 Tg Fe yr−1). The simulated DFe concentrations show a satisfactory comparison with available observations, indicating an atmospheric burden of ∼0.007 Tg Fe, and overall resulting in an atmospheric deposition flux into the global ocean of 0.376 ± 0.005 Tg Fe yr−1, well within the range reported in the literature. All in all, this work is a first step towards the development of EC-Earth into an Earth System Model with fully interactive bioavailable atmospheric Fe inputs to the marine biogeochemistry component of the model.

Atmospheric deposition of soluble iron (Fe) to the ocean has an impact on oceanic primary productivity, thus on carbon dioxide uptake. Understanding how anthropogenic activity influences the atmospheric Fe cycle is key to project ocean biogeochemical cycles and has been barely explored.In this study, we assess past, present, and future soluble Fe deposition to the ocean, accounting for natural and anthropogenic sources, using an advanced atmospheric Fe cycle module implemented into the EC-Earth3 Earth System Model. This version of the model considers primary emissions of insoluble and soluble Fe forms associated with dust minerals, and anthropogenic and biomass burning combustion aerosols. Fe solubilization processes in the atmosphere include 1) proton-promoted, 2) oxalate-promoted (with oxalate calculated on-line), and 3) photo-reductive Fe dissolution. We run time-slice simulations using the atmosphere-chemistry model configuration constrained by past, present, and future ocean states. The necessary sea surface temperature and sea ice concentration climatologies are obtained from EC-Earth3 CMIP6 coupled model experiments. Future projections rely on three CMIP6 scenarios representing different socio-economic pathways and end-of-the-century forcing levels: SSP1-2.6, SSP2-4.5, and SSP3-7.0. Our setup allows us to estimate the soluble Fe deposition into the ocean while quantifying the contribution from dust, biomass burning, and anthropogenic combustion sources separately under a range of scenarios. Our preliminary results suggest nearly a 50% increase in soluble Fe deposition for the present time since the industrial revolution, attributed to increased atmospheric acidity and oxalate concentrations that result in a more efficient atmospheric processing. Future projections of soluble Fe show a high correlation between anthropogenic activity and solubility of deposited Fe, scenarios with higher anthropogenic emissions consistently yield a higher fraction of soluble over total deposited Fe. Our results also suggest diverging trends for the different ocean basins. Disentangling the factors that drive those differences in regions where Fe is known to be the limiting nutrient, such as the North Pacific or the Southern Ocean, is fundamental to improve our understanding of the atmospheric Fe cycle and its consequences for the ocean biogeochemistry.

Changing atmospheric acidity alters the delivery of nutrients to the ocean and affects marine productivity and ecology., Anthropogenic emissions to the atmosphere have increased the flux of nutrients, especially nitrogen, to the ocean, but they have also altered the acidity of aerosol, cloud water, and precipitation over much of the marine atmosphere. For nitrogen, acidity-driven changes in chemical speciation result in altered partitioning between the gas and particulate phases that subsequently affect long-range transport. Other important nutrients, notably iron and phosphorus, are affected, because their soluble fractions increase upon exposure to acidic environments during atmospheric transport. These changes affect the magnitude, distribution, and deposition mode of individual nutrients supplied to the ocean, the extent to which nutrient deposition interacts with the sea surface microlayer during its passage into bulk seawater, and the relative abundances of soluble nutrients in atmospheric deposition. Atmospheric acidity change therefore affects ecosystem composition, in addition to overall marine productivity, and these effects will continue to evolve with changing anthropogenic emissions in the future.

Aerosol-cloud interactions are one of the major sources of uncertainty in climate projections. Ice Nuclei Particles (INP) significantly affect the radiative properties, cloud lifetime and precipitation rates due to their ability to form ice at temperatures higher than those of homogeneous ice nucleation. The majority of related studies investigate INP that originates from K-feldspar mineral desert dust particles and marine organic particles. In the present study we further investigate the contribution of terrestrial bio-aerosols to INP concentration via immersion freezing using the global 3-D chemistry transport model TM4-ECPL. The available and potential INP concentrations in the atmosphere at ambient and given temperature, respectively, are derived from model simulated dust, marine organics, and terrestrial bacteria, fungi and pollen using experimentally-deduced parameterizations of ice-active surface site density for each type of aerosol acting as INP. It is found that INP from desert dust dominates the concentration of INP over the entire Northern Hemisphere, terrestrial bio-aerosols contribute to INP concentration mainly close to the emission sources, while marine organics are important contributors to INP over remote oceans depending on marine biota, which varies seasonally.

State-of-the-art global nutrient deposition fields are coupled here to the Pelagic Interactions Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemistry model to investigate their effect on ocean biogeochemistry in the context of atmospheric forcings for pre-industrial, present, and future periods. PISCES, as part of the European Community Earth system model (EC-Earth) model suite, runs in offline mode using prescribed dynamical fields as simulated by the Nucleus for European Modelling of the Ocean (NEMO) ocean model. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P into the global ocean account for ∼ 40 Tg N yr−1, ∼ 0.28 Tg Fe yr−1, and ∼ 0.10 Tg P yr−1. Pre-industrial atmospheric nutrient deposition fluxes are lower compared to the present day (∼ 51 %, ∼ 36 %, and ∼ 40 % for N, Fe, and P, respectively). However, the overall impact on global productivity is low (∼ 3 %) since a large part of marine productivity is driven by nutrients recycled in the upper ocean layer or other local factors. Prominent changes are, nevertheless, found for regional productivity. Reductions of up to 20 % occur in oligotrophic regions such as the subtropical gyres in the Northern Hemisphere under pre-industrial conditions. In the subpolar Pacific, reduced pre-industrial Fe fluxes lead to a substantial decline of siliceous diatom production and subsequent accumulation of Si, P, and N, in the subpolar gyre. Transport of these nutrient-enriched waters leads to strongly elevated production of calcareous nanophytoplankton further south and southeast, where iron no longer limits productivity. The North Pacific is found to be the most sensitive to variations in depositional fluxes, mainly because the water exchange with nutrient-rich polar waters is hampered by land bridges. By contrast, large amounts of unutilized nutrients are advected equatorward in the Southern Ocean and North Atlantic, making these regions less sensitive to external nutrient inputs. Despite the lower aerosol N : P ratios with respect to the Redfield ratio during the pre-industrial period, the nitrogen fixation decreased in the subtropical gyres mainly due to diminished iron supply. Future changes in air pollutants under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario result in a modest decrease of the atmospheric nutrients inputs into the global ocean compared to the present day (∼ 13 %, ∼ 14 %, and ∼ 20 % for N, Fe, and P, respectively), without significantly affecting the projected primary production in the model. Sensitivity simulations further show that the impact of atmospheric organic nutrients on the global oceanic productivity has turned out roughly as high as the present-day productivity increase since the pre-industrial era when only the inorganic nutrients' supply is considered in the model. On the other hand, variations in atmospheric phosphorus supply have almost no effect on the calculated oceanic productivity.

Atmospheric deposition can be an important source of nutrients and trace elements for land and ocean ecosystems. Atmospheric acidity is an important driver of the solubility of nutrients and trace elements present in atmospheric aerosols. Using a global 3-dimensional chemical transport model, we summarize here human driven past and future changes in the aerosol acidity and the resulting changes in the nitrogen, phosphorus and iron atmospheric deposition and solubility. We present and discuss the acidity driven changes in the chemical speciation and geographic patterns of nutrient deposition. Areas of uncertainties and implications for ecosystems functioning are discussed.This work has been supported by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund) and by the University of Bremen Excellence Chair of MK.

Atmospheric deposition of trace constituents of natural and anthropogenic origin act as a nutrient source into the open ocean, affecting the marine ecosystem functioning and subsequently the exchange of CO2 between the atmosphere and the global ocean. Among other species that are deposited into the open ocean, nitrogen (N), iron (Fe), and phosphorus (P) are considered as highly significant nutrients that can limit marine phytoplankton growth and thus directly impact on ocean carbon fluxes in the ocean, particularly where the nutrient availability is the limiting factor for productivity. For this work, we take into account the up-to-date understanding of the effects of air quality on the atmospheric aerosol cycles to investigate the potential ocean biogeochemistry perturbations via the atmospheric input with the European Community Earth System Model EC-Earth (http://www.ec-earth.org/), which is jointly developed by several European institutes. In more detail, state-of-the-art N, Fe, and P atmospheric deposition fields are coupled to the embedded marine biogeochemistry model and the response of oceanic biogeochemistry to natural and anthropogenic atmospheric aerosols deposition changes is demonstrated and quantified. Model calculations show that compared to the present day, the preindustrial atmospheric deposition fluxes are calculated lower (~1.7, ~1.5, and ~1.4 times for N, Fe, and P, respectively) corresponding to a respective lower marine primary production. On the other hand, future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean (~ -15%, ~ -16% and ~ -22% for N, Fe and P, respectively) and overall to a slightly lower projected export production compared to present day. Although the impact of atmospheric processing on atmospheric inputs to the ocean results in a relatively weak response in total global-scale simulated marine productivity estimates, strong regional changes up to 40-60% are calculated in the subtropical gyres. Overall, this study indicates that both the atmospheric processing and the speciation of the atmospheric nutrients deposited in the ocean should be considered in detail in carbon-cycling studies, since they may significantly affect the marine ecosystems and thus the current estimates of the carbon cycle feedbacks to climate.This work has been financed by the National Observatory of Athens internal grant (number 5065), the “Atmospheric deposition impacts on the ocean system”, and the European Commission's Horizon 2020 Framework Programme, under Grant Agreement number 641816, the "Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination, and Outreach (CRESCENDO)".

Aerosol acidity (pH) plays a significant role in the chemical behaviour of atmospheric particles, since it affects their composition and toxicity. This study investigates the seasonal variability of submicron particles acidity at the Finokalia atmospheric observatory in the eastern Mediterranean from February to December 2014. Direct measurements of aerosol pH are challenging and thus very rare. Therefore, aerosol pH is generally derived from thermodynamic model calculations. Submicron aerosol chemical composition data along with NH3 and HNO3 gas phase concentrations measured at Finokalia are here used in the thermodynamic model ISORROPIA-II in order to predict the aerosol pH. The predicted pH values show clear seasonality and the expected dependence on temperature and relative humidity. Submicron aerosols at Finokalia have been found to be acidic with an average pH values over the studied period of 1.77 ± 0.67, with the highest values occurring in winter and the lowest in summer and a winter to summer ratio of about 1.4.We acknowledge support of this work by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).

Limited area models applied at higher resolution than global models and using datasets of higher resolution are generally expected to more accurately represent the spatiotemporal variability of key meteorological and climate parameters such as near surface temperature, pressure, wind speed and atmospheric composition. However, limited area models require boundary conditions and the accuracy of such datasets reflects on the accuracy of the mesoscale simulations of atmospheric composition, in particular of the longer-lived species. The effects of various resolution meteorological data and of different chemical boundary and initial conditions on the simulated concentrations of the chemical gases and aerosols in the Mediterranean have been here investigated. Two different simulations in three domains of progressively increasing horizontal resolution were performed for the year 2016 using the mesoscale Weather Research and Forecasting (WRF) meteorological model with the chemistry module (WRF-Chem) and an additional one with different chemical boundary and initial conditions. Meteorology from the Global Forecast System (GFS) at two different horizontal resolutions (1 × 1° and 0.25 × 0.25°) available from NOAA has been used in the model to investigate their impact on the simulated air pollutants. The higher resolution meteorological input improves the comparison of model results to observations. The results are found sensitive to the chemical boundary and initial conditions.

Acidification of airborne dust particles can dramatically increase the amount of bioavailable phosphorus (P) deposited on the surface ocean. Experiments were conducted to simulate atmospheric processes and determine the dissolution behavior of P compounds in dust and dust precursor soils. Acid dissolution occurs rapidly (seconds to minutes) and is controlled by the amount of H+ions present. For H+< 10−4mol/g of dust, 1–10% of the total P is dissolved, largely as a result of dissolution of surface-bound forms. At H+> 10−4mol/g of dust, the amount of P (and calcium) released has a direct proportionality to the amount of H+consumed until all inorganic P minerals are exhausted and the final pH remains acidic. Once dissolved, P will stay in solution due to slow precipitation kinetics. Dissolution of apatite-P (Ap-P), the major mineral phase in dust (79–96%), occurs whether calcium carbonate (calcite) is present or not, although the increase in dissolved P is greater if calcite is absent or if the particles are externally mixed. The system was modeled adequately as a simple mixture of Ap-P and calcite. P dissolves readily by acid processes in the atmosphere in contrast to iron, which dissolves more slowly and is subject to reprecipitation at cloud water pH. We show that acidification can increase bioavailable P deposition over large areas of the globe, and may explain much of the previously observed patterns of variability in leachable P in oceanic areas where primary productivity is limited by this nutrient (e.g., Mediterranean).

Air pollution creates high Fe solubility in pyrogenic aerosols, raising the flux of biologically essential Fe to the oceans., Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity.

A total of sixteen global chemistry transport models and general circulation models have participated in this study. Fourteen models have been evaluated with regard to their ability to reproduce near-surface observed number concentration of aerosol particle and cloud condensation nuclei (CCN), and derived cloud droplet number concentration (CDNC). Model results for the period 2011–2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations, located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments, and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of −24 % and −35 % for particles with dry diameters > 50 nm and > 120 nm and −36 % and −34 % for CCN at supersaturations of 0.2 % and 1.0 %, respectively. Fifteen models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40 % during winter and 20 % in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB −17 % and −22 % for updraft velocities 0.3 and 0.6 m s−1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally-derived value at lower than at higher updraft velocities (index-of-agreement of 0.47 vs 0.50). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration and to updraft velocity. Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high.

A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011–2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of −24 % and −35 % for particles with dry diameters >50 and >120 nm, as well as −36 % and −34 % for CCN at supersaturations of 0.2 % and 1.0 %, respectively. However, they seem to behave differently for particles activating at very low supersaturations ( %) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2 % (CCN0.2) compared to that for N3, maximizing over regions where new particle formation is important. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40 % during winter and 20 % in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB −13 % and −22 % for updraft velocities 0.3 and 0.6 m s−1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally derived values at lower than at higher updraft velocities (index of agreement 0.64 vs. 0.65). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration (∂Nd/∂Na) and to updraft velocity (∂Nd/∂w). Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high. Discrepancies are found in sensitivities ∂Nd/∂Na and ∂Nd/∂w; models may be predisposed to be too “aerosol sensitive” or “aerosol insensitive” in aerosol–cloud–climate interaction studies, even if they may capture average droplet numbers well. This is a subtle but profound finding that only the sensitivities can clearly reveal and may explain inter-model biases on the aerosol indirect effect.

It is well recognized that the atmospheric deposition of iron (Fe) affects ocean productivity, atmospheric CO2 uptake, ecosystem diversity, and overall climate. Despite significant advances in measurement techniques and modeling efforts, discrepancies persist between observations and models that hinder accurate predictions of processes and their global effects. Here, we provide an assessment report on where the current state of knowledge is and where future research emphasis would have the highest impact in furthering the field of Fe atmosphere-ocean biogeochemical cycle. These results were determined through consensus reached by diverse researchers from the oceanographic and atmospheric science communities with backgrounds in laboratory and in situ measurements, modeling, and remote sensing. We discuss i) novel measurement methodologies and instrumentation that allow detection and speciation of different forms and oxidation states of Fe in deliquesced mineral aerosol, cloud/rainwater, and seawater; ii) oceanic models that treat Fe cycling with several external sources and sinks, dissolved, colloidal, particulate, inorganic, and organic ligand-complexed forms of Fe, as well as Fe in detritus and phytoplankton; and iii) atmospheric models that consider natural and anthropogenic sources of Fe, mobilization of Fe in mineral aerosols due to the dissolution of Fe-oxides and Fe-substituted aluminosilicates through proton-promoted, organic ligand-promoted, and photo-reductive mechanisms. In addition, the study identifies existing challenges and disconnects (both fundamental and methodological) such as i) inconsistencies in Fe nomenclature and the definition of bioavailable Fe between oceanic and atmospheric disciplines, and ii) the lack of characterization of the processes controlling Fe speciation and residence time at the atmosphere-ocean interface. Such challenges are undoubtedly caused by extremely low concentrations, short lifetime, and the myriad of physical, (photo)chemical, and biological processes affecting global biogeochemical cycling of Fe. However, we also argue that the historical division (separate treatment of Fe biogeochemistry in oceanic and atmospheric disciplines) and the classical funding structures (that often create obstacles for transdisciplinary collaboration) are also hampering the advancement of knowledge in the field. Finally, the study provides some specific ideas and guidelines for laboratory studies, field measurements, and modeling research required for improved characterization of global biogeochemical cycling of Fe in relationship with other trace elements and essential nutrients. The report is intended to aid scientists in their work related to Fe biogeochemistry as well as program managers at the relevant funding agencies.

The Mediterranean Sea is an oligotrophic semi-closed environment where atmospheric deposition is expected to be an important driver for biological activity. The present study uses a three-dimensional atmospheric chemistry transport model to evaluate the nitrogen (N), phosphorus (P) and iron (Fe) atmospheric deposition fluxes to the Mediterranean Sea. The model takes into account both the inorganic and organic fractions of these fluxes and compares them to other sources of these nutrients that are external to the ocean. The estimated atmospheric deposition fluxes of soluble nutrients amount to 1281 Gg-N y−1, 4.31 Gg-P y−1 and 6.32 Gg-Fe y−1 for the present day, and are within the range of the few estimates available in literature. An almost 6-fold increase in the atmospheric deposition of soluble N is also calculated to be the result of the increase in anthropogenic and biomass burning emissions since 1850, while soluble P and Fe deposition fluxes have increased by 59% and 114%, respectively. For future (2100) emissions, however, N deposition is projected to increase only slightly (4%) while soluble P and Fe fluxes will decrease by 34% and 32% compared to current estimates. The soluble organic N and P annual deposition fluxes are calculated to be 12% and 28–83% of total soluble N and P present-day annual deposition fluxes into the Mediterranean Sea, respectively. However, to reconcile with the observed fluxes in the west and the east Mediterranean, ∼14 times higher flux of soluble P, in particular organic P, and at least 2.5 times higher flux of soluble Fe need to be considered in the model. Such high fluxes can be due to higher combustion emissions of soluble Fe and P, to higher dust emissions or solubilisation of Fe and P contained in dust aerosols, and also higher organic P flux associated with bioaerosols than currently used in the global models. Overall, the calculated deposition fluxes provide an integrated spatially complete picture of the atmospheric inputs to the Mediterranean marine ecosystem, which are potentially important for net primary production and the ocean carbon cycle.

The capability of global chemistry and transport models (CTMs) to simulate atmospheric composition and its spatial and temporal changes highly relies on the input data used by the models, in particular the emission inventories. Biomass burning emissions show large spatial, diurnal, seasonal and year-to-year variability. In the present study, we applied a global 3-D CTM to evaluate uncertainties in the computed atmospheric composition associated with the use of different biomass burning emissions and identify areas where observational data can help to reduce these uncertainties. We find the emission inventory choice to lead to regional differences in the calculated load of aerosols up to a factor of 4. Assumptions on the injection height of the biomass burning emissions are found to produce regionally up to 30% differences in the calculated tropospheric lifetimes of pollutants. Computed changes in lifetimes point to a strong chemical feedback mechanism between emissions from biomass burning and isoprene emissions from vegetation that are linked via NOx-driven oxidant chemistry, NOx-dependent changes in isoprene oxidation products, aerosol emissions and atmospheric transport. These interactions reduce isoprene load in the presence of biomass burning emissions by 15%, calculated for the same amount of isoprene emitted into the troposphere. Thus, isoprene load and lifetime are inversely related to the quantities of pollutants emitted by biomass burning. These interactions are shown to be able to increase the global annual secondary aerosol yield from isoprene emissions, defined as the ratio of tropospheric loads of secondary aerosol from isoprene oxidation to isoprene emissions, by up to 18%.

International Technical Meeting on Air Pollution Modelling and its Application 2016; International audience; A set of global 3-dimensional model simulations have been performed to investigate the changes in atmospheric composition driven by humans. Sensitivity simulations using past, present and future anthropogenic emissions of pollutants are analyzed to derive the importance of human-driven emissions of pollutants for aerosol composition, including aerosol water, and for dust aerosol aging. The results show that applied emission control has significantly limited air pollution levels compared to a hypothetical uncontrolled situation. They also point out that human activities have increased atmospheric acidity and as a result the solubility of nutrients, like iron and phosphorus, in atmospheric deposition.

International audience; The performance of the coupled mesoscale meteorology and chemistry model WRF/CHEM to simulate the atmospheric composition over the Mediterranean is here evaluated. The model configuration applied for this study uses the gas phase chemical mechanism Mozart and a spatial resolution of 36 × 36 km, which nests in lower resolutions (12 × 12 km and 7.2 × 7.2 km). Anthropogenic surface emissions developed in the frame of the ECLIPSE EU FP7 project and biomass burning emissions from the FINN database are used. Mineral dust aerosol emissions are derived from the GOCART dust model and biogenic emissions are calculated online by the MEGAN model. The global 3-dimensional chemistry-transport model TM4-ECPL is providing the initial and boundaries chemical conditions for the coarse resolution mesoscale model. The results show that the mesoscale model overestimates O3 surface levels at most stations by up to about 70 % and underestimates CO surface levels by up to about 25 %. Strong correlations between simulations and observations are computed for 60 % of the studied O3 stations and 20 % of the studied CO stations. No significant change in the model performance as a function of the studied model resolutions was found.

The main objective of the present study is the assessment of the non-radiative impact on the lower troposphere air quality of the intense biomass burning events that took place in the Eastern Mediterranean, when wild forest fires were burning in Peloponnesus (Greece) at the end of August 2007. The MM5-CAMx modeling system was applied in the Eastern Mediterranean in high spatial and temporal resolution for the period 23 to 31 August 2007, forced by biomass burning emission fluxes from the Global Fire Emissions Database (version 3.0), in day-to-day temporal and 0.1° spatial variability from the Global Fire Assimilation System. Enhancements of the CO and NOx concentrations over almost the entire modeling domain were estimated due to the biomass burning, which were more pronounced over the burnt areas and maximum over the Peloponnesus forest fires. The domain-wide near surface mean concentration was higher by + 6% for CO and + 11% for NOx because of the biomass burning. The near surface O 3 values were reduced over the fire hot spots but increased over the greater part of the modeling domain. On the 26th August 2007, the maximum O 3 concentrations reduction of about 12 ppb (i.e. − 34%) was calculated over the Peloponnesus fires while the highest O 3 increase of about 27 ppb (i.e. + 52%) was estimated over the sea at 500 km downwind the Peloponnesus large forest fires. The process analysis revealed that on that day, the inclusion of the biomass burning emissions resulted in an enhancement of the daytime gas phase O 3 production in the boundary layer in the Eastern Mediterranean and during some daytime hours in a change of the chemical regime from O 3 destruction to O 3 production. From 6 to 16 UTC, the O 3 photochemistry in the boundary layer was VOC-sensitive close to the Peloponnesus fires, gradually changing to NOx-sensitive in the downwind fire plume. In the same period, the maximum impact on the oxidizing capacity of the boundary layer was an increase by 0.25 ppt for OH and a reduction by 13 ppt for HO 2 mean concentrations over the Peloponnesus forest fires and an increase by 12 ppt for HO 2 in the downwind plume.

The atmospheric cycle of phosphorus (P) is parameterized here in a state-of-the-art global 3-D chemistry transport model, taking into account primary emissions of total P (TP) and soluble P (DP) associated with mineral dust, combustion particles from natural and anthropogenic sources, bioaerosols, sea spray and volcanic aerosols. For the present day, global TP emissions are calculated to be roughly 1.33 Tg-P yr−1, with the mineral sources contributing more than 80 % to these emissions. The P solubilization from mineral dust under acidic atmospheric conditions is also parameterized in the model and is calculated to contribute about one-third (0.14 Tg-P yr−1) of the global DP atmospheric source. To our knowledge, a unique aspect of our global study is the explicit modeling of the evolution of phosphorus speciation in the atmosphere. The simulated present-day global annual DP deposition flux is 0.45 Tg-P yr−1 (about 40 % over oceans), showing a strong spatial and temporal variability. Present-day simulations of atmospheric P aerosol concentrations and deposition fluxes are satisfactory compared with available observations, indicating however an underestimate of about 70 % on current knowledge of the sources that drive the P atmospheric cycle. Sensitivity simulations using preindustrial (year 1850) anthropogenic and biomass burning emission scenarios showed a present-day increase of 75 % in the P solubilization flux from mineral dust, i.e., the rate at which P is converted into soluble forms, compared to preindustrial times, due to increasing atmospheric acidity over the last 150 years. Future reductions in air pollutants due to the implementation of air-quality regulations are expected to decrease the P solubilization flux from mineral dust by about 30 % in the year 2100 compared to the present day. Considering, however, that all the P contained in bioaerosols is readily available for uptake by marine organisms, and also accounting for all other DP sources, a total bioavailable P flux of about 0.17 Tg-P yr−1 to the oceans is derived. Our calculations further show that in some regions more than half of the bioavailable P deposition flux to the ocean can originate from biological particles, while this contribution is found to maximize in summer when atmospheric deposition impact on the marine ecosystem is the highest due to ocean stratification. Thus, according to this global study, a largely unknown but potentially important role of terrestrial bioaerosols as suppliers of bioavailable P to the global ocean is also revealed. Overall, this work provides new insights to the atmospheric P cycle by demonstrating that biological materials are important carriers of bioavailable P, with very important implications for past and future responses of marine ecosystems to global change.

The Mediterranean basin, as a crossroad of air masses from different origin, is affected by aerosol of different size, composition and properties, including desert dust transported from Africa. Aerosol remote sensing techniques provide a great opportunity for the observation and the understanding of the aerosols behavior since they allow systematic and extended spatial and temporal sampling of the atmosphere. Cloud Condensation Nuclei (CCN) are aerosol particles which provide surface area for water condensation, enhancing formation of cloud droplets. Cloud Condensation Nuclei Level–3 daily product from Moderate Resolution Imaging Spectroradiometer (MODIS), sorted into 1 by 1 degree grids, has been acquired from MODIS website (modis.gsfc.nasa.gov) in order to investigate the impact of dust transport to CCN formation over the Mediterranean. The number of CCN in the atmospheric column, as retrieved at the spectral band of 550 nm during major dust events, indicate that mineral dust episodes lead to higher values of CCN (up to 10 times higher) than observed under background conditions. The derived CCN column concentrations over the Mediterranean for a reference day vary between 2x108 and 5x108 cm−2, whereas, during dust cases, the values typically range between 3x108 and 2x109 cm−2.

Primary Biological Aerosol Particles (PBAPs), commonly known also as bioaerosols, are airborne particles that include mainly bacteria, fungi spores, pollen, viruses, microorganisms or even leaf debris and usually dominate the aerosol mass over remote forested regions. The atmospheric cycle of PBAPs is here parameterized in a state-of-the-art global 3-D chemistry-transport model by taking into account their primary emissions as well as their chemical aging during the long-range transport in the atmosphere. Different ecosystems are used to parameterize the respective flux rates of PBAPs considering bacteria, fungal spores and pollen, and using meteorological parameters in order to account for fluxes seasonal variation. Bioaerosols are assumed to be emitted as 50 % hydrophilic particles but they can be transferred to the soluble mode via atmospheric oxidation, changing thus their physical properties and their atmospheric lifetime. The global annual flux of PBAPs to the atmosphere calculated by the model equals about 123 Tg yr−1 (47.5 Tg-C yr−1) and the atmospheric burden is calculated to equal about 791 Gg. These calculated emissions largely depend on the assumed size distribution and is comparable to the amount of primary particulate organic carbon injected into the atmosphere by anthropogenic emissions.

During the last 30 years significant effort has been made to improve air quality through legislation for emissions reduction. Global three-dimensional chemistry-transport simulations of atmospheric composition changes over the past three decades have been performed to assess the impact of these measures. The simulations are based on assimilated meteorology to account for the year-to-year observed climate variability and on different anthropogenic emissions scenarios of pollutants which may or may not account for air quality legislation application. The ACCMIP dataset historical emissions are used as the starting point. We show that air quality legislation has been more efficient than thought in limiting the rapid increase of air pollutants due to significant technology development. The achieved reductions in nitrogen oxides, carbon monoxide, black carbon and sulphate aerosols are found to be significant when comparing to simulations neglecting legislation for the protection of the environment. We also show the large tropospheric air-quality benefit from the development of cleaner technology. These 30-year hindcast simulations demonstrate that the actual benefit in air quality due to air pollution legislation and technological advances is higher than the gain calculated by a simple comparison against a constant anthropogenic emissions simulation, as is usually done. Our results also indicate that over China and India the beneficial technological advances for the air-quality have been masked by the explosive increase in local population and the disproportional increase in energy demand.

International audience; The importance of the long-range transport (LRT) on O3 and CO budgets over the Eastern Mediterranean has been investigated using the state-of-the-art 3-dimensional global chemistry-transport model TM4-ECPL. A 3-D budget analysis has been performed separating the Eastern from the Western basins and the boundary layer (BL) from the free troposphere (FT). The FT of the Eastern Mediterranean is shown to be a strong receptor of polluted air masses from the Western Mediterranean, and the most important source of polluted air masses for the Eastern Mediterranean BL, with about 40% of O3 and of CO in the BL to be transported from the FT aloft. Regional anthropogenic sources are found to have relatively small impact on regional air quality in the area, contributing by about 8% and 18% to surface levels of O3 and CO, respectively. Projections using anthropogenic emissions for the year 2050 but neglecting climate change calculate a surface O3 decrease of about 11% together with a surface CO increase of roughly 10% in the Eastern Mediterranean.