Nikos Daskalakis

Past, Present, and Future Atmospheric Nitrogen Deposition

Reactive nitrogen emissions into the atmosphere are increasing due to human activities, affecting nitrogen deposition to the surface and impacting the productivity of terrestrial and marine ecosystems. An atmospheric chemistry-transport model (TM4-ECPL) is here used to calculate the global distribution of total nitrogen deposition, accounting for the first time for both its inorganic and organic fractions in gaseous and particulate phases, and past and projected changes due to anthropogenic activities. The anthropogenic and biomass burning ACCMIP historical and RCP6.0 and RCP8.5 emissions scenarios are used. Accounting for organic nitrogen (ON) primary emissions, the present-day global nitrogen atmospheric source is about 60% anthropogenic, while total N deposition increases by about 20% relative to simulations without ON primary emissions. About 20-25% of total deposited N is ON. About 10% of the emitted nitrogen oxides are deposited as ON instead of inorganic nitrogen (IN) as is considered in most global models. Almost a 3-fold increase over land (2-fold over the ocean) has been calculated for soluble N deposition due to human activities from 1850 to present. The investigated projections indicate significant changes in the regional distribution of N deposition and chemical composition, with reduced compounds gaining importance relative to oxidized ones, but very small changes in the global total flux. Sensitivity simulations quantify uncertainties due to the investigated model parameterizations of IN partitioning onto aerosols and of N chemically fixed on organics to be within 10% for the total soluble N deposition and between 25-35% for the dissolved ON deposition. Larger uncertainties are associated with N emissions.

Linking 31P magnetic shielding tensors to crystal structures: experimental and theoretical studies on metal(II) aminotris(methylenephosphonates).

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

Mapping the supramolecular chemistry of pyrazole-4-sulfonate: layered inorganic–organic networks with Zn2+, Cd2+, Ag+, Na+ and NH4+, and their use in copper anticorrosion protective films

Five compounds based on the versatile pyrazole-4-sulfonate anion (4-SO3-pzH = L−) were synthesized by the reaction of ligand HL with ZnO, CdCO3, Ag2O, NaOH and NH3, respectively. Crystals of Zn(4-SO3-pzH)2(H2O)2, Cd(4-SO3-pzH)2(H2O)2, Ag(4-SO3-pzH), Na(4-SO3-pzH)(H2O) and NH4(4-SO3-pzH) were obtained from aqueous solutions upon evaporation, and were characterized by single-crystal X-ray diffraction, IR and NMR spectroscopy, thermogravimetric analysis and copper corrosion inhibition experiments. We found that the non-isomorphous, 3-dimensional inorganic–organic layered solid state structure of these compounds is determined by an intricate interplay between the size, charge and coordination preference of the cation, and an extended lattice of hydrogen bonds and aromatic interactions. Ligand L− incorporates a host of different binding capabilities (metal coordination through the pyrazole N-atom and/or the sulfonate O-atom, hydrogen-bonding both as donor and acceptor, π–π and C–H⋯π interactions). Thin films formed by these complexes on copper metal surfaces were studied by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. ZnL2, CdL2, AgL and NH4L, in addition to the free ligand HL, were tested as corrosion inhibitors on copper metal surfaces at three different pH values (2, 3 and 4), and the corrosion rates were quantified. Significant corrosion protection was observed with all compounds at pH 4 and 3.

Observation- and Model-Based Estimates of Particulate Dry Nitrogen Deposition to the Oceans

Anthropogenic nitrogen (N) emissions to the atmosphere have increased significantly the deposition of nitrate (NO3-) and ammonium (NH4+) to the surface waters of the open ocean, with potential impacts on marine productivity and the global carbon cycle. Global-scale understanding of the impacts of N deposition to the oceans is reliant on our ability to produce and validate models of nitrogen emission, atmospheric chemistry, transport and deposition. In this work, ~2900 observations of aerosol NO3- and NH4+ concentrations, acquired from sampling aboard ships in the period 1995 - 2012, are used to assess the performance of modelled N concentration and deposition fields over the remote ocean. Three ocean regions (the eastern tropical North Atlantic, the northern Indian Ocean and northwest Pacific) were selected, in which the density and distribution of observational data were considered sufficient to provide effective comparison to model products. All of these study regions are affected by transport and deposition of mineral dust, which alters the deposition of N, due to uptake of nitrogen oxides (NOx) on mineral surfaces. Assessment of the impacts of atmospheric N deposition on the ocean requires atmospheric chemical transport models to report deposition fluxes, however these fluxes cannot be measured over the ocean. Modelling studies such as the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), which only report deposition flux are therefore very difficult to validate for dry deposition. Here the available observational data were averaged over a 5° × 5° grid and compared to ACCMIP dry deposition fluxes (ModDep) of oxidised N (NOy) and reduced N (NHx) and to the following parameters from the TM4-ECPL (TM4) model: ModDep for NOy, NHx and particulate NO3- and NH4+, and surface-level particulate NO3- and NH4+ concentrations. As a model ensemble, ACCMIP can be expected to be more robust than TM4, while TM4 gives access to speciated parameters (NO3- and NH4+) that are more relevant to the observed parameters and which are not available in ACCMIP. Dry deposition fluxes (CalDep) were calculated from the observed concentrations using estimates of dry deposition velocities. Model - observation ratios, weighted by grid-cell area and numbers of observations, (RA,n) were used to assess the performance of the models. Comparison in the three study regions suggests that TM4 over-estimates NO3- concentrations (RA,n = 1.4 - 2.9) and under-estimates NH4+ concentrations (RA,n = 0.5 - 0.7), with spatial distributions in the tropical Atlantic and northern Indian Ocean not being reproduced by the model. In the case of NH4+ in the Indian Ocean, this discrepancy was probably due to seasonal biases in the sampling. Similar patterns were observed in the various comparisons of CalDep to ModDep (RA,n = 0.6 - 2.6 for NO3-, 0.6 - 3.1 for NH4+). Values of RA,n for NHx CalDep - ModDep comparisons were approximately double the corresponding values for NH4+ CalDep - ModDep comparisons due to the significant fraction of gas-phase NH3 deposition incorporated in the TM4 and ACCMIP NHx model products. All of the comparisons suffered due to the scarcity of observational data and the large uncertainty in dry deposition velocities used to derive deposition fluxes from concentrations. These uncertainties have been a major limitation on estimates of the flux of material to the oceans for several decades. Recommendations are made for improvements in N deposition estimation through changes in observations, modelling and model - observation comparison procedures. Validation of modelled dry deposition requires effective comparisons to observable aerosol-phase species concentrations and this cannot be achieved if model products only report dry deposition flux over the ocean.

Simulated air quality and pollutant budgets over Europe in 2008

Major gaseous and particulate pollutant levels over Europe in 2008 have been simulated using the offline-coupled WRFCMAQ chemistry and transport modeling system. The simulations are compared with surface observations from the EMEP stations, ozone (O3) soundings, ship-borne O3 and nitrogen dioxide (NO2) observations in the western Mediterranean, tropospheric NO2 vertical column densities from the SCIAMACHY instrument, and aerosol optical depths (AOD) from the AERONET. The results show that on average, surface O3 levels are underestimated by 4 to 7% over the northern European EMEP stations while they are overestimated by 7-10% over the southern European EMEP stations and underestimated in the tropospheric column (by 10-20%). Particulate matter (PM) mass concentrations are underestimated by up to 60%, particularly in southern and eastern Europe, suggesting underestimated PM sources. Larger differences are calculated for individual aerosol components, particularly for organic and elemental carbon than for the total PM mass, indicating uncertainty in the combustion sources. Better agreement has been obtained for aerosol species over urban areas of the eastern Mediterranean, particularly for nss-SO4(2), attributed to the implementation of higher quality emission inventories for that area. Simulated AOD levels are lower than the AERONET observations by 10% on average, with average underestimations of 3% north of 40°N, attributed to the low anthropogenic emissions in the model and 22% south of 40°N, suggesting underestimated natural and resuspended dust emissions. Overall, the results reveal differences in the model performance between northern and southern Europe, suggesting significant differences in the representation of both anthropogenic and natural emissions in these regions. Budget analyses indicate that O3 and peroxyacetyl nitrate (PAN) are transported from the free troposphere (FT) to the planetary boundary layer over Europe, while other species follow the reverse path and are then advected away from the source region.

SALSA2.0: The sectional aerosol module of theaerosol-chemistry-climate model ECHAM6.3.0-HAM2.3-MOZ1.0

In this paper, we present the implementation and evaluation of the aerosol microphysics module SALSA2.0 in the framework of the aerosol-chemistry-climate model ECHAM-HAMMOZ. It is an alternative microphysics module to the default modal microphysics scheme M7 in ECHAM-HAMMOZ. The SALSA2.0 implementation is evaluated against the observations of aerosol optical properties, aerosol mass, and size distributions. We also compare the skill of SALSA2.0 in reproducing the observed quantities to the skill of the M7 implementation. The largest differences between SALSA2.0 and M7 are evident 5 over regions where the aerosol size distribution is heavily modified by the microphysical processing of aerosol particles. Such regions are, for example, highly polluted regions and regions strongly affected by biomass burning. In addition, in a simulation of the 1991 Mt Pinatubo eruption in which a stratospheric sulfate plume was formed, the global burden and the effective radii of the stratospheric aerosol are very different in SALSA2.0 and M7. While SALSA2.0 was able to reproduce the observed time evolution of the global burden of sulfate and the effective radii of stratospheric aerosol, M7 strongly overestimates the removal 10 of coarse stratospheric particles and thus underestimates the effective radius of stratospheric aerosol. As the mode widths of M7 have been optimized for the troposphere and were not designed to represent stratospheric aerosol the ability of M7 to simulate 1 Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-47 Manuscript under review for journal Geosci. Model Dev. Discussion started: 3 April 2018 c

Study of the Impact of an Intense Biomass Burning Event on the Air Quality in the Eastern Mediterranean

Aim of this work is to study the impact of the intense forest fires that tookplace in Greece at the end of summer 2007 on the air quality in the Eastern Mediterranean. For this reason the meteorological model MM5 and the photochemical model CAMx are applied over the study area with 10 km spatial resolution. CAMx model is implemented for two emission scenarios; with and without biomass burning emissions. High spatial resolution wildfire emission data are used that are based on the Global Fire Emissions Database (GFED3). The CAMx chemical boundary conditions are taken from the TM4 global model. The nonradiative impact on the composition of the atmosphere and on environmental indices (e.g. Aggregate Risk Index) is quantified in regional scale. The impact of the atmospheric processes on the air pollution levels due to the biomass burning event is also studied giving more emphasis on the boundary layer. The intense biomass burning event in the Eastern Mediterranean at the end of August 2007 results in an enhancement of the CO, NOx and PM2.5 concentrations over almost all the study area, which can range from several times to two order of magnitude over the fire hot spots. The increases in O3 levels are less pronounced and are found mainly downwind the burnt areas. On the 25th August 2007, when fire counts in the study area are maximum, in the daytime boundary layer, the inclusion of biomass burning emissions results in a change of the chemical regime from O3 destruction to O3 production.

Formation and growth of atmospheric nanoparticles in the eastern Mediterranean: Results from long-term measurements and process simulations

Atmospheric new particle formation (NPF) is a common phenomenon all over the world. In this study we present the longest time series of NPF records in the eastern Mediterranean region by analyzing 10 years of aerosol number size distribution data obtained with a mobility particle sizer. The measurements were performed at the Finokalia environmental research station on Crete, Greece, during the period June 2008–June 2018. We found that NPF took place on 27 % of the available days, undefined days were 23 % and non-event days 50 %. NPF is more frequent in April and May probably due to the terrestrial biogenic activity and is less frequent in August. Throughout the period under study, nucleation was observed also during the night. Nucleation mode particles had the highest concentration in winter and early spring, mainly because of the minimum sinks, and their average contribution to the total particle number concentration was 8 %. Nucleation mode particle concentrations were low outside periods of active NPF and growth, so there are hardly any other local sources of sub-25 nm particles. Additional atmospheric ion size distribution data simultaneously collected for more than 2 years were also analyzed. Classification of NPF events based on ion spectrometer measurements differed from the corresponding classification based on a mobility spectrometer, possibly indicating a different representation of local and regional NPF events between these two measurement data sets. We used the MALTE-Box model for simulating a case study of NPF in the eastern Mediterranean region. Monoterpenes contributing to NPF can explain a large fraction of the observed NPF events according to our model simulations. However the adjusted parameterization resulting from our sensitivity tests was significantly different from the initial one that had been determined for the boreal environment. Published by Copernicus Publications on behalf of the European Geosciences Union. 2672 N. Kalivitis et al.: Formation and growth of atmospheric nanoparticles in the eastern Mediterranean

Simulations of New Particle Formation and Growth Processes at Eastern Mediterranean, with the MALTE-Box Model

Simulations of New Particle Formation (NPF) events observed at Finokalia research station of the University of Crete were performed using MALTE-Box. The MALTE-box is a 0-d model that simulates chemical and aerosol dynamical processes with the use of a size-segregated aerosol model, UHMA (University Helsinki Multicomponent Aerosol Model). Measurements from Finokalia station and results from numerical simulations were used as input data in the model. Specifically, biogenic and anthropogenic emissions were taken from the global three-dimensional chemistry-transport model TM4-ECPL. Α case study was performed, during which an ‘‘event’’ and a ‘‘non event’’ week in August 2012 were simulated. During the ‘‘event’’ week new particle formation was detected at Finokalia station, whereas this didn’t happen during the ‘‘non event’’ week. During the ‘‘event week’’ the simulations of NPF capture the day that NPF is observed. However, they underestimate the growth rate of the newly formed particles when compared to observations. Simulations improve when measurements of monoterpenes at Finokalia station are used as input to the model that computes new particles growth rate by ELVOC and SVOC issued from monoterpenes chemistry.

Human Driven Changes in Atmospheric Aerosol Composition

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.