Maria Kanakidou - Academia.edu (original) (raw)

Papers by Maria Kanakidou

Springer eBooks, 2021

This section reviews current knowledge on the impacts of air pollution on human health as well as... more This section reviews current knowledge on the impacts of air pollution on human health as well as marine and terrestrial ecosystems in the Mediterranean. The first chapter summarizes the human health studies in the region, with special focus on the impact of dust and biomass burning events. The last two chapters concentrate on the impact of air quality on the marine and terrestrial ecosystems summarizing relevant knowledge from studies performed in the Mediterranean. Content total 76 pp.

Ice-nucleating particles (INPs) enable ice formation, profoundly affecting the microphysical and ... more 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.

Atmospheric Chemistry and Physics Discussions, 2019

A total of sixteen global chemistry transport models and general circulation models have particip... more 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 > 50nm 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 N 3 (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

Atmospheric Chemistry and Physics Discussions, 2018

Atmospheric New Particle Formation (NPF) is a common phenomenon all over the world. In this study... more 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 seven 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 2015. We found that NPF took place 29% of the available days, undefined days were 26% and non-event days 45%. NPF is more frequent in April and May probably due to the biogenic activity and is less frequent in August and November. The NPF frequency increased during the measurement period, while particle growth rates showed a decreasing trend, indicating possible changes in the ambient sulfur dioxide concentrations in the area. Throughout the period under study, we frequently observed production of particles in the nucleation mode during night-time, a feature rarely observed in the ambient atmosphere. Nucleation mode particles had the highest concentration in winter, mainly because of the minimum sinks, and their average contribution to the total particle number concentration was 9%. 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 two years period were also analyzed. Classification of NPF events based on ion measurements differed from the corresponding classification based on mobility spectrometer measurements, possibly indicating a different representation of local and regional NPF events between these two measurement data sets. We used MALTE-box model for a simulation 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 parametrization that resulted after sensitivity tests was significantly different from the one applied for the boreal environment. 1) Introduction Most of the atmospheric aerosol particles, and a substantial fraction of particles able to act as cloud condensation nuclei (CCN), have been estimated to originate from new particle formation (NPF) taking place in the atmosphere (Spracklen et al. 2006; Kerminen et al., 2012; Gordon et al., 2017). The exact mechanisms driving atmospheric NPF and subsequent particle growth processes are still not fully understood, nor are the roles of different vapors and ions in these processes (

Biogeosciences, 2018

This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and... more This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, "The Atmospheric Input of Chemicals to the Ocean". The global total Fe (TFe) emission strength in the models is equal to ∼ 72 Tg Fe yr −1 (38-134 Tg Fe yr −1) from mineral dust sources and around 2.1 Tg Fe yr −1 (1.8-2.7 Tg Fe yr −1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr −1 , accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10-30 and 0.2-0.4 Tg Fe yr −1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3 Tg Fe yr −1 for the multi-model ensemble model mean.

Environmental Research Letters, 2018

Atmospheric aerosols have complex and variable compositions and properties. While scientific inte... more Atmospheric aerosols have complex and variable compositions and properties. While scientific interest is centered on the health and climatic effects of atmospheric aerosols, insufficient attention is given to their involvement in multiphase chemistry that alters their contribution as carriers of nutrients in ecosystems. However, there is experimental proof that the nutrient equilibria of both land and marine ecosystems have been disturbed during the Anthropocene period. This review study first summarizes our current understanding of aerosol chemical processing in the atmosphere as relevant to biogeochemical cycles. Then it binds together results of recent modeling studies based on laboratory and field experiments, focusing on the organic and dust components of aerosols that account for multiphase chemistry, aerosol ageing in the atmosphere, nutrient (N, P, Fe) emissions, atmospheric transport, transformation and deposition. The human-driven contribution to atmospheric deposition of these nutrients, derived by global simulations using past and future anthropogenic emissions of pollutants, is put into perspective with regard to potential changes in nutrient limitations and biodiversity. Atmospheric deposition of nutrients has been suggested to result in human-induced ecosystem limitations with regard to specific nutrients. Such modifications favor the development of certain species against others and affect the overall functioning of ecosystems. Organic forms of nutrients are found to contribute to the atmospheric deposition of the nutrients N, P and Fe by 20%-40%, 35%-45% and 7%-18%, respectively. These have the potential to be key components of the biogeochemical cycles since there is initial proof of their bioavailability to ecosystems. Bioaerosols have been found to make a significant contribution to atmospheric sources of N and P, indicating potentially significant interactions between terrestrial and marine ecosystems. These results deserve further experimental and modeling studies to reduce uncertainties and understand the feedbacks induced by atmospheric deposition of nutrients to ecosystems.

Atmospheric Chemistry and Physics, 2016

During the last 30 years, significant effort has been made to improve air quality through legisla... more During the last 30 years, significant effort has been made to improve air quality through legislation for emissions reduction. Global three-dimensional chemistrytransport simulations of atmospheric composition over the past 3 decades have been performed to estimate what the air quality levels would have been under a scenario of stagnation of anthropogenic emissions per capita as in 1980, accounting for the population increase (BA1980) or using the standard practice of neglecting it (AE1980), and how they compare to the historical changes in air quality levels. The simulations are based on assimilated meteorology to account for the yearto-year observed climate variability and on different scenarios of anthropogenic emissions of pollutants. The ACCMIP historical emissions dataset is used as the starting point. Our sensitivity simulations provide clear indications that air quality legislation and technology developments have limited the rapid increase of air pollutants. The achieved reductions in concentrations of nitrogen oxides, carbon monoxide, black carbon, and sulfate aerosols are found to be significant when comparing to both BA1980 and AE1980 simulations that neglect any measures applied for the protection of the environment. We also show the potentially large tropospheric air quality benefit from the development of cleaner technology used by the growing global population. These 30-year hindcast sensitivity 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 may have been masked by the explosive increase in local population and the disproportional increase in energy demand partially due to the globalization of the economy.

Biogeosciences Discussions, 2016

The atmospheric cycle of phosphorus (P) is here parameterized in a global 3-D chemistry-transport... more The atmospheric cycle of phosphorus (P) is here parameterized in a global 3-D chemistry-transport model, taking into account primary emissions of total P (TP) and dissolved P (DP) associated with mineral dust, combustion particles of natural and anthropogenic sources, bioaerosols, sea-spray and volcanic aerosols. Global TP emissions are calculated to amount roughly 1.33 Tg-P yr-1 with mineral sources (about 1.10 Tg-P yr-1) contributing more than 80% to these emissions. Additionally, under acidic atmospheric conditions, for the present study we take into account the P mobilization from 20 mineral dust, that is calculated to contribute about one third (0.14 Tg-P yr-1) to the global DP atmospheric source. The calculated global annual DP deposition flux equals to 0.43 Tg-P yr-1 (about 40% enters the ocean), and shows a strong spatial and temporal variability. Considering that all bioaerosol P is bioavailable (BP) and accounting for all other sources of DP, a flux of 0.16 Tg-P yr-1 BP to the ocean is derived. Present day simulations of atmospheric P aerosol concentrations and deposition fluxes are satisfactory compared with available observations, indicating however a 50% uncertainty of current 25 knowledge on primary and secondary sources of P that drive its atmospheric cycle. Sensitivity simulations using preindustrial (year 1850) and future (2100) anthropogenic and biomass burning emission scenarios, showed a present-day increase of 75% in the dissolution flux of P present in dust aerosol compared to the 1850 dissolution flux 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 P mobilization flux by about 30% for the year 2100 compared to the present-day. A 30 striking result is that more than 50% of the BP deposition flux to the ocean originates from biological particle and this contribution is found to maximize in summer when atmospheric deposition impact on the marine ecosystem is the highest due to ocean stratification. These findings reveal the largely unknown but important role of terrestrial bioaerosols as suppliers of bioavailable P to the oceanwith very important implications for past and future responses of ecosystems to global change. Therefore, our study provides new insights to the atmospheric P cycle by demonstrating that bioaerosols are 35 as important carriers of bioavailable P as dust aerosol, that was up to now considered as the only large source of DP external to the open ocean.

Biogeosciences Discussions, 2015

The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport mode... more The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport model TM4-ECPL to simulate the proton-and the organic ligandpromoted mineral-Fe dissolution as well as the aqueousphase photochemical reactions between the oxidative states of Fe (III/II). Primary emissions of total (TFe) and dissolved (DFe) Fe associated with dust and combustion processes are also taken into account, with TFe mineral emissions calculated to amount to ∼ 35 Tg-Fe yr −1 and TFe emissions from combustion sources of ∼ 2 Tg-Fe yr −1. The model reasonably simulates the available Fe observations, supporting the reliability of the results of this study. Proton-and organic ligand-promoted Fe dissolution in present-day TM4-ECPL simulations is calculated to be ∼ 0.175 Tg-Fe yr −1 , approximately half of the calculated total primary DFe emissions from mineral and combustion sources in the model (∼ 0.322 Tg-Fe yr −1). The atmospheric burden of DFe is calculated to be ∼ 0.024 Tg-Fe. DFe deposition presents strong spatial and temporal variability with an annual flux of ∼ 0.496 Tg-Fe yr −1 , from which about 40 % (∼ 0.191 Tg-Fe yr −1) is deposited over the ocean. The impact of air quality on Fe deposition is studied by performing sensitivity simulations using preindustrial (year 1850), present (year 2008) and future (year 2100) emission scenarios. These simulations indicate that about a 3 times increase in Fe dissolution may have occurred in the past 150 years due to increasing anthropogenic emissions and thus atmospheric acidity. Air-quality regulations of anthropogenic emissions are projected to decrease atmospheric acidity in the near future, reducing to about half the dust-Fe dissolution relative to the present day. The organic ligand contribution to Fe dissolution shows an inverse relationship to the atmospheric acidity, thus its importance has decreased since the preindustrial period but is projected to increase in the future. The calculated changes also show that the atmospheric DFe supply to the globe has more than doubled since the preindustrial period due to 8fold increases in the primary non-dust emissions and about a 3-fold increase in the dust-Fe dissolution flux. However, in the future the DFe deposition flux is expected to decrease (by about 25 %) due to reductions in the primary non-dust emissions (about 15 %) and in the dust-Fe dissolution flux (about 55 %). The present level of atmospheric deposition of DFe over the global ocean is calculated to be about 3 times higher than for 1850 emissions, and about a 30 % decrease is projected for 2100 emissions. These changes are expected to impact most on the high-nutrient-low-chlorophyll oceanic regions.

Atmospheric Chemistry and Physics Discussions, 2011

Megacities are large urban agglomerations with intensive anthropogenic emissions that have signif... more Megacities are large urban agglomerations with intensive anthropogenic emissions that have significant impacts on local and regional air quality. In the present mesoscale modeling study, the impacts of anthropogenic emissions from the Greater Istanbul Area (GIA) and the Greater Athens Area (GAA) on the air quality in GIA, GAA and the entire East Mediterranean are quantified for typical wintertime (December 2008) and summertime (July 2008) conditions. They are compared to those of the regional anthropogenic and biogenic emissions that are also calculated. Finally, the efficiency of potential country-based emissions mitigation in improving air quality is investigated. The results show that relative contributions from both cities to surface ozone (O 3) and aerosol levels in the cities' extended areas are generally higher in winter than in summer. Anthropogenic emissions from GIA depress surface O 3 in the GIA by ∼ 60 % in winter and ∼ 20 % in summer while those from GAA reduce the surface O 3 in the GAA by 30 % in winter and by 8 % in summer. GIA and GAA anthropogenic emissions contribute to the fine particulate matter (PM 2.5) levels inside the cities themselves by up to 75 % in winter and by 50 % (GIA) and ∼ 40 % (GAA), in summer. GIA anthropogenic emissions have larger impacts on the domain-mean surface O 3 (up to 1 %) and PM 2.5 (4 %) levels compared to GAA anthropogenic emissions (< 1 % for O 3 and ≤ 2 % for PM 2.5) in both seasons. Impacts of regional anthropogenic emissions on the domain-mean surface pollutant levels (up to 17 % for summertime O 3 and 52 % for wintertime fine particulate matter, PM 2.5) are much higher than those from Istanbul and Athens together (∼ 1 % for O 3 and ∼ 6 % for PM 2.5 , respectively). Regional biogenic emissions are found to limit the production of secondary inorganic aerosol species in summer up to 13 % (non-sea-salt sulfate (nss-SO 2− 4) in rural Athens) due to their impact on oxidant levels while they have negligible impact in winter. Finally, the responses to country-based anthropogenic emission mitigation scenarios inside the studied region show increases in O 3 mixing ratios in the urban areas of GIA and GAA, higher in winter (∼ 13 % for GIA and 2 % for GAA) than in summer (∼ 7 % for GIA and < 1 % for GAA). On the opposite PM 2.5 concentrations decrease by up to 30 % in GIA and by 20 % in GAA with the highest improvements computed for winter. The emission reduction strategy also leads to domain-wide decreases in most primary pollutants like carbon monoxide (CO) or nitrogen oxides (NO x) for both seasons. The results show the importance of long range transport of pollutants for the air quality in the East Mediterranean. Thus, improvements of air quality in the East Mediterranean require coordinated efforts inside the region and beyond.

Atmospheric Chemistry and Physics, 2014

Science of The Total Environment, 2014

Major pollutant levels are simulated over Europe for the year 2008. • Ozone levels are overestima... more Major pollutant levels are simulated over Europe for the year 2008. • Ozone levels are overestimated while aerosol levels are underestimated. • Updated emissions over East Mediterranean result in better agreement with observations. • Emission distributions and photochemistry lead to a north-south gradient.

Journal of Geophysical Research, 1994

Acetone (CH3COCH 3) was found to be the dominant nonmethane organic species present in the atmosp... more Acetone (CH3COCH 3) was found to be the dominant nonmethane organic species present in the atmosphere sampled primarily over eastern Canada (0-6 kin, 35ø-65øN) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (=10-12 v/v) with a mean value of 1140 + 413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios of 550 _+ 100 ppt were present in much of the troposphere studied. Correlations between atmospheric mixing ratios of acetone and select species such as C2H2, CO, C3H8, C2C14 and isoprene provided important clues to its possible sources and to the causes of its atmospheric variability. Biomass burning as a source of acetone has been identified for the first time. By using atmospheric data and three-dimensional photochemical models, a global acetone source of 40-60 Tg (=1012 g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons (principally propane, isobutane, and isobutene) provides the single largest source (51%). The remainder is attributable to biomass burning (26%), direct biogenic emissions (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also suggest that acetone photolysis contributed significantly to PAN formation (100-200 ppt) in .the middle and upper troposphere of the sampled region and may be important globally. While the source-sink equation appears to be roughly balanced, much more atmospheric and source data, especially from the southern hemisphere, are needed to reliably quantify the atmospheric budget of acetone. 103 Tg/yr [Duce et al., 1983; Singh and Zimmerman, 1992]. Atmospheric reactions of these NMHCs with ozone (03) and free radicals result in the formation of a variety of intermediate oxygenated species of which carbonyls (RR'C=O) form an important group [National Academy of Sciences (NAS, 1976; Lloyd, 1979; Atkinson, 1990]. There is further evidence that direct emissions of carbonyl species from both natural and manmade sources are also quite common [NAS, 1976; Isidorov et al., 1985; Sigsby et al., 1987]. Carbonyl compounds are of interest to atmospheric chemists because of their potential toxicity, their ability to photolyze and produce free radicals, their ability to form stable atmospheric products, and their interactions in the smog cycles. Because they are frequently intermediate products of atmospheric oxidation, these molecules can serve as excellent tracers for the validation of photochemical models.

Journal of Geophysical Research, 1995

Global Biogeochemical Cycles, 2012

The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is reex... more The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is reexamined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3-dimensional chemistry-transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from 33% to 90% (median of 335%) of total soluble N in rainwater; soluble OP ranges from 20−8320-83% (median of 20−8335%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with 4545% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model-derived present-day soluble ON and OP deposition to the global ocean is estimated to be 4516 Tg-N/yr and 0.35Tg−P/yrrespectivelywithanorderofmagnitudeuncertainty.Oftheseamounts0.35 Tg-P/yr respectively with an order of magnitude uncertainty. Of these amounts 0.35Tg−P/yrrespectivelywithanorderofmagnitudeuncertainty.Oftheseamounts40% and $6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P-limitation in the oligotrophic regions of the world's ocean that rely on atmospheric deposition as an important nutrient source.

Atmospheric Environment, 2013

h i g h l i g h t s Atmospheric N and S depositions over Mediterranean and Black seas are simulat... more h i g h l i g h t s Atmospheric N and S depositions over Mediterranean and Black seas are simulated. N transported from upwind sources is deposited over the Mediterranean. Dry deposition dominates over wet deposition in Mediterranean and Black Sea. Atmospheric N inputs are comparable to N export in Black and W. Mediterranean seas. Atmospheric N input exceeds the N export in the East Mediterranean Sea.

Atmospheric Chemistry and Physics, 2011

Changes in temperature due to variability in meteorology and climate change are expected to signi... more Changes in temperature due to variability in meteorology and climate change are expected to significantly impact atmospheric composition. The Mediterranean is a climate sensitive region and includes megacities like Istanbul and large urban agglomerations such as Athens. The effect of temperature changes on gaseous air pollutant levels and the atmospheric processes that are controlling them in the Eastern Mediterranean are here investigated. The WRF/CMAQ mesoscale modeling system is used, coupled with the MEGAN model for the processing of biogenic volatile organic compound emissions. A set of temperature perturbations (spanning from 1 to 5 K) is applied on a base case simulation corresponding to July 2004. The results indicate that the Eastern Mediterranean basin acts as a reservoir of pollutants and their precursor emissions from large urban agglomerations. During summer, chemistry is a major sink at these urban areas near the surface, and a minor contributor at downwind areas. On average, the atmospheric processes are more effective within the first 1000 m above ground. Temperature increases lead to increases in biogenic emissions by 9 ± 3% K −1. Ozone mixing ratios increase almost linearly with the increases in ambient temperatures by 1±0.1 ppb O 3 K −1 for all studied urban and receptor stations except for Istanbul, where a 0.4±0.1 ppb O 3 K −1 increase is calculated, which is about half of the domain-averaged increase of 0.9 ± 0.1 ppb O 3 K −1. The computed changes in atmospheric processes are also linearly related with temperature changes.

Atmospheric Chemistry and Physics, 2012

Megacities are large urban agglomerations with intensive anthropogenic emissions that have signif... more Megacities are large urban agglomerations with intensive anthropogenic emissions that have significant impacts on local and regional air quality. In the present mesoscale modeling study, the impacts of anthropogenic emissions from the Greater Istanbul Area (GIA) and the Greater Athens Area (GAA) on the air quality in GIA, GAA and the entire East Mediterranean are quantified for typical wintertime (December 2008) and summertime (July 2008) conditions. They are compared to those of the regional anthropogenic and biogenic emissions that are also calculated. Finally, the efficiency of potential country-based emissions mitigation in improving air quality is investigated. The results show that relative contributions from both cities to surface ozone (O 3) and aerosol levels in the cities' extended areas are generally higher in winter than in summer. Anthropogenic emissions from GIA depress surface O 3 in the GIA by ∼ 60 % in winter and ∼ 20 % in summer while those from GAA reduce the surface O 3 in the GAA by 30 % in winter and by 8 % in summer. GIA and GAA anthropogenic emissions contribute to the fine particulate matter (PM 2.5) levels inside the cities themselves by up to 75 % in winter and by 50 % (GIA) and ∼ 40 % (GAA), in summer. GIA anthropogenic emissions have larger impacts on the domain-mean surface O 3 (up to 1 %) and PM 2.5 (4 %) levels compared to GAA anthropogenic emissions (< 1 % for O 3 and ≤ 2 % for PM 2.5) in both seasons. Impacts of regional anthropogenic emissions on the domain-mean surface pollutant levels (up to 17 % for summertime O 3 and 52 % for wintertime fine particulate matter, PM 2.5) are much higher than those from Istanbul and Athens together (∼ 1 % for O 3 and ∼ 6 % for PM 2.5 , respectively). Regional biogenic emissions are found to limit the production of secondary inorganic aerosol species in summer up to 13 % (non-sea-salt sulfate (nss-SO 2− 4) in rural Athens) due to their impact on oxidant levels while they have negligible impact in winter. Finally, the responses to country-based anthropogenic emission mitigation scenarios inside the studied region show increases in O 3 mixing ratios in the urban areas of GIA and GAA, higher in winter (∼ 13 % for GIA and 2 % for GAA) than in summer (∼ 7 % for GIA and < 1 % for GAA). On the opposite PM 2.5 concentrations decrease by up to 30 % in GIA and by 20 % in GAA with the highest improvements computed for winter. The emission reduction strategy also leads to domain-wide decreases in most primary pollutants like carbon monoxide (CO) or nitrogen oxides (NO x) for both seasons. The results show the importance of long range transport of pollutants for the air quality in the East Mediterranean. Thus, improvements of air quality in the East Mediterranean require coordinated efforts inside the region and beyond.

Atmospheric Chemistry and Physics, 2011

Organic acids attract increasing attention as contributors to atmospheric acidity, secondary orga... more Organic acids attract increasing attention as contributors to atmospheric acidity, secondary organic aerosol mass and aerosol hygroscopicity. Oxalic acid is globally the most abundant dicarboxylic acid, formed via chemical oxidation of gas-phase precursors in the aqueous phase of aerosols and droplets. Its lifecycle and atmospheric global distribution remain highly uncertain and are the focus of this study. The first global spatial and temporal distribution of oxalate, simulated using a state-of-the-art aqueous-phase chemical scheme embedded within the global 3-dimensional chemistry/transport model TM4-ECPL, is here presented. The model accounts for comprehensive gas-phase chemistry and its coupling with major aerosol constituents (including secondary organic aerosol). Model results are consistent with ambient observations of oxalate at rural and remote locations (slope = 1.16 ± 0.14, r 2 = 0.36, N =114) and suggest that aqueous-phase chemistry contributes significantly to the global atmospheric burden of secondary organic aerosol. In TM4-ECPL most oxalate is formed in-cloud and less than 5 % is produced in aerosol water.

Atmospheric Chemistry and Physics, 2005

The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance fo... more The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.

Springer eBooks, 2021

This section reviews current knowledge on the impacts of air pollution on human health as well as... more This section reviews current knowledge on the impacts of air pollution on human health as well as marine and terrestrial ecosystems in the Mediterranean. The first chapter summarizes the human health studies in the region, with special focus on the impact of dust and biomass burning events. The last two chapters concentrate on the impact of air quality on the marine and terrestrial ecosystems summarizing relevant knowledge from studies performed in the Mediterranean. Content total 76 pp.

Ice-nucleating particles (INPs) enable ice formation, profoundly affecting the microphysical and ... more 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.

Atmospheric Chemistry and Physics Discussions, 2019

A total of sixteen global chemistry transport models and general circulation models have particip... more 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 > 50nm 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 N 3 (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

Atmospheric Chemistry and Physics Discussions, 2018

Atmospheric New Particle Formation (NPF) is a common phenomenon all over the world. In this study... more 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 seven 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 2015. We found that NPF took place 29% of the available days, undefined days were 26% and non-event days 45%. NPF is more frequent in April and May probably due to the biogenic activity and is less frequent in August and November. The NPF frequency increased during the measurement period, while particle growth rates showed a decreasing trend, indicating possible changes in the ambient sulfur dioxide concentrations in the area. Throughout the period under study, we frequently observed production of particles in the nucleation mode during night-time, a feature rarely observed in the ambient atmosphere. Nucleation mode particles had the highest concentration in winter, mainly because of the minimum sinks, and their average contribution to the total particle number concentration was 9%. 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 two years period were also analyzed. Classification of NPF events based on ion measurements differed from the corresponding classification based on mobility spectrometer measurements, possibly indicating a different representation of local and regional NPF events between these two measurement data sets. We used MALTE-box model for a simulation 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 parametrization that resulted after sensitivity tests was significantly different from the one applied for the boreal environment. 1) Introduction Most of the atmospheric aerosol particles, and a substantial fraction of particles able to act as cloud condensation nuclei (CCN), have been estimated to originate from new particle formation (NPF) taking place in the atmosphere (Spracklen et al. 2006; Kerminen et al., 2012; Gordon et al., 2017). The exact mechanisms driving atmospheric NPF and subsequent particle growth processes are still not fully understood, nor are the roles of different vapors and ions in these processes (

Biogeosciences, 2018

This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and... more This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, "The Atmospheric Input of Chemicals to the Ocean". The global total Fe (TFe) emission strength in the models is equal to ∼ 72 Tg Fe yr −1 (38-134 Tg Fe yr −1) from mineral dust sources and around 2.1 Tg Fe yr −1 (1.8-2.7 Tg Fe yr −1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr −1 , accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10-30 and 0.2-0.4 Tg Fe yr −1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3 Tg Fe yr −1 for the multi-model ensemble model mean.

Environmental Research Letters, 2018

Atmospheric aerosols have complex and variable compositions and properties. While scientific inte... more Atmospheric aerosols have complex and variable compositions and properties. While scientific interest is centered on the health and climatic effects of atmospheric aerosols, insufficient attention is given to their involvement in multiphase chemistry that alters their contribution as carriers of nutrients in ecosystems. However, there is experimental proof that the nutrient equilibria of both land and marine ecosystems have been disturbed during the Anthropocene period. This review study first summarizes our current understanding of aerosol chemical processing in the atmosphere as relevant to biogeochemical cycles. Then it binds together results of recent modeling studies based on laboratory and field experiments, focusing on the organic and dust components of aerosols that account for multiphase chemistry, aerosol ageing in the atmosphere, nutrient (N, P, Fe) emissions, atmospheric transport, transformation and deposition. The human-driven contribution to atmospheric deposition of these nutrients, derived by global simulations using past and future anthropogenic emissions of pollutants, is put into perspective with regard to potential changes in nutrient limitations and biodiversity. Atmospheric deposition of nutrients has been suggested to result in human-induced ecosystem limitations with regard to specific nutrients. Such modifications favor the development of certain species against others and affect the overall functioning of ecosystems. Organic forms of nutrients are found to contribute to the atmospheric deposition of the nutrients N, P and Fe by 20%-40%, 35%-45% and 7%-18%, respectively. These have the potential to be key components of the biogeochemical cycles since there is initial proof of their bioavailability to ecosystems. Bioaerosols have been found to make a significant contribution to atmospheric sources of N and P, indicating potentially significant interactions between terrestrial and marine ecosystems. These results deserve further experimental and modeling studies to reduce uncertainties and understand the feedbacks induced by atmospheric deposition of nutrients to ecosystems.

Atmospheric Chemistry and Physics, 2016

During the last 30 years, significant effort has been made to improve air quality through legisla... more During the last 30 years, significant effort has been made to improve air quality through legislation for emissions reduction. Global three-dimensional chemistrytransport simulations of atmospheric composition over the past 3 decades have been performed to estimate what the air quality levels would have been under a scenario of stagnation of anthropogenic emissions per capita as in 1980, accounting for the population increase (BA1980) or using the standard practice of neglecting it (AE1980), and how they compare to the historical changes in air quality levels. The simulations are based on assimilated meteorology to account for the yearto-year observed climate variability and on different scenarios of anthropogenic emissions of pollutants. The ACCMIP historical emissions dataset is used as the starting point. Our sensitivity simulations provide clear indications that air quality legislation and technology developments have limited the rapid increase of air pollutants. The achieved reductions in concentrations of nitrogen oxides, carbon monoxide, black carbon, and sulfate aerosols are found to be significant when comparing to both BA1980 and AE1980 simulations that neglect any measures applied for the protection of the environment. We also show the potentially large tropospheric air quality benefit from the development of cleaner technology used by the growing global population. These 30-year hindcast sensitivity 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 may have been masked by the explosive increase in local population and the disproportional increase in energy demand partially due to the globalization of the economy.

Biogeosciences Discussions, 2016

The atmospheric cycle of phosphorus (P) is here parameterized in a global 3-D chemistry-transport... more The atmospheric cycle of phosphorus (P) is here parameterized in a global 3-D chemistry-transport model, taking into account primary emissions of total P (TP) and dissolved P (DP) associated with mineral dust, combustion particles of natural and anthropogenic sources, bioaerosols, sea-spray and volcanic aerosols. Global TP emissions are calculated to amount roughly 1.33 Tg-P yr-1 with mineral sources (about 1.10 Tg-P yr-1) contributing more than 80% to these emissions. Additionally, under acidic atmospheric conditions, for the present study we take into account the P mobilization from 20 mineral dust, that is calculated to contribute about one third (0.14 Tg-P yr-1) to the global DP atmospheric source. The calculated global annual DP deposition flux equals to 0.43 Tg-P yr-1 (about 40% enters the ocean), and shows a strong spatial and temporal variability. Considering that all bioaerosol P is bioavailable (BP) and accounting for all other sources of DP, a flux of 0.16 Tg-P yr-1 BP to the ocean is derived. Present day simulations of atmospheric P aerosol concentrations and deposition fluxes are satisfactory compared with available observations, indicating however a 50% uncertainty of current 25 knowledge on primary and secondary sources of P that drive its atmospheric cycle. Sensitivity simulations using preindustrial (year 1850) and future (2100) anthropogenic and biomass burning emission scenarios, showed a present-day increase of 75% in the dissolution flux of P present in dust aerosol compared to the 1850 dissolution flux 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 P mobilization flux by about 30% for the year 2100 compared to the present-day. A 30 striking result is that more than 50% of the BP deposition flux to the ocean originates from biological particle and this contribution is found to maximize in summer when atmospheric deposition impact on the marine ecosystem is the highest due to ocean stratification. These findings reveal the largely unknown but important role of terrestrial bioaerosols as suppliers of bioavailable P to the oceanwith very important implications for past and future responses of ecosystems to global change. Therefore, our study provides new insights to the atmospheric P cycle by demonstrating that bioaerosols are 35 as important carriers of bioavailable P as dust aerosol, that was up to now considered as the only large source of DP external to the open ocean.

Biogeosciences Discussions, 2015

The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport mode... more The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport model TM4-ECPL to simulate the proton-and the organic ligandpromoted mineral-Fe dissolution as well as the aqueousphase photochemical reactions between the oxidative states of Fe (III/II). Primary emissions of total (TFe) and dissolved (DFe) Fe associated with dust and combustion processes are also taken into account, with TFe mineral emissions calculated to amount to ∼ 35 Tg-Fe yr −1 and TFe emissions from combustion sources of ∼ 2 Tg-Fe yr −1. The model reasonably simulates the available Fe observations, supporting the reliability of the results of this study. Proton-and organic ligand-promoted Fe dissolution in present-day TM4-ECPL simulations is calculated to be ∼ 0.175 Tg-Fe yr −1 , approximately half of the calculated total primary DFe emissions from mineral and combustion sources in the model (∼ 0.322 Tg-Fe yr −1). The atmospheric burden of DFe is calculated to be ∼ 0.024 Tg-Fe. DFe deposition presents strong spatial and temporal variability with an annual flux of ∼ 0.496 Tg-Fe yr −1 , from which about 40 % (∼ 0.191 Tg-Fe yr −1) is deposited over the ocean. The impact of air quality on Fe deposition is studied by performing sensitivity simulations using preindustrial (year 1850), present (year 2008) and future (year 2100) emission scenarios. These simulations indicate that about a 3 times increase in Fe dissolution may have occurred in the past 150 years due to increasing anthropogenic emissions and thus atmospheric acidity. Air-quality regulations of anthropogenic emissions are projected to decrease atmospheric acidity in the near future, reducing to about half the dust-Fe dissolution relative to the present day. The organic ligand contribution to Fe dissolution shows an inverse relationship to the atmospheric acidity, thus its importance has decreased since the preindustrial period but is projected to increase in the future. The calculated changes also show that the atmospheric DFe supply to the globe has more than doubled since the preindustrial period due to 8fold increases in the primary non-dust emissions and about a 3-fold increase in the dust-Fe dissolution flux. However, in the future the DFe deposition flux is expected to decrease (by about 25 %) due to reductions in the primary non-dust emissions (about 15 %) and in the dust-Fe dissolution flux (about 55 %). The present level of atmospheric deposition of DFe over the global ocean is calculated to be about 3 times higher than for 1850 emissions, and about a 30 % decrease is projected for 2100 emissions. These changes are expected to impact most on the high-nutrient-low-chlorophyll oceanic regions.

Atmospheric Chemistry and Physics Discussions, 2011

Megacities are large urban agglomerations with intensive anthropogenic emissions that have signif... more Megacities are large urban agglomerations with intensive anthropogenic emissions that have significant impacts on local and regional air quality. In the present mesoscale modeling study, the impacts of anthropogenic emissions from the Greater Istanbul Area (GIA) and the Greater Athens Area (GAA) on the air quality in GIA, GAA and the entire East Mediterranean are quantified for typical wintertime (December 2008) and summertime (July 2008) conditions. They are compared to those of the regional anthropogenic and biogenic emissions that are also calculated. Finally, the efficiency of potential country-based emissions mitigation in improving air quality is investigated. The results show that relative contributions from both cities to surface ozone (O 3) and aerosol levels in the cities' extended areas are generally higher in winter than in summer. Anthropogenic emissions from GIA depress surface O 3 in the GIA by ∼ 60 % in winter and ∼ 20 % in summer while those from GAA reduce the surface O 3 in the GAA by 30 % in winter and by 8 % in summer. GIA and GAA anthropogenic emissions contribute to the fine particulate matter (PM 2.5) levels inside the cities themselves by up to 75 % in winter and by 50 % (GIA) and ∼ 40 % (GAA), in summer. GIA anthropogenic emissions have larger impacts on the domain-mean surface O 3 (up to 1 %) and PM 2.5 (4 %) levels compared to GAA anthropogenic emissions (< 1 % for O 3 and ≤ 2 % for PM 2.5) in both seasons. Impacts of regional anthropogenic emissions on the domain-mean surface pollutant levels (up to 17 % for summertime O 3 and 52 % for wintertime fine particulate matter, PM 2.5) are much higher than those from Istanbul and Athens together (∼ 1 % for O 3 and ∼ 6 % for PM 2.5 , respectively). Regional biogenic emissions are found to limit the production of secondary inorganic aerosol species in summer up to 13 % (non-sea-salt sulfate (nss-SO 2− 4) in rural Athens) due to their impact on oxidant levels while they have negligible impact in winter. Finally, the responses to country-based anthropogenic emission mitigation scenarios inside the studied region show increases in O 3 mixing ratios in the urban areas of GIA and GAA, higher in winter (∼ 13 % for GIA and 2 % for GAA) than in summer (∼ 7 % for GIA and < 1 % for GAA). On the opposite PM 2.5 concentrations decrease by up to 30 % in GIA and by 20 % in GAA with the highest improvements computed for winter. The emission reduction strategy also leads to domain-wide decreases in most primary pollutants like carbon monoxide (CO) or nitrogen oxides (NO x) for both seasons. The results show the importance of long range transport of pollutants for the air quality in the East Mediterranean. Thus, improvements of air quality in the East Mediterranean require coordinated efforts inside the region and beyond.

Atmospheric Chemistry and Physics, 2014

Science of The Total Environment, 2014

Major pollutant levels are simulated over Europe for the year 2008. • Ozone levels are overestima... more Major pollutant levels are simulated over Europe for the year 2008. • Ozone levels are overestimated while aerosol levels are underestimated. • Updated emissions over East Mediterranean result in better agreement with observations. • Emission distributions and photochemistry lead to a north-south gradient.

Journal of Geophysical Research, 1994

Acetone (CH3COCH 3) was found to be the dominant nonmethane organic species present in the atmosp... more Acetone (CH3COCH 3) was found to be the dominant nonmethane organic species present in the atmosphere sampled primarily over eastern Canada (0-6 kin, 35ø-65øN) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (=10-12 v/v) with a mean value of 1140 + 413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios of 550 _+ 100 ppt were present in much of the troposphere studied. Correlations between atmospheric mixing ratios of acetone and select species such as C2H2, CO, C3H8, C2C14 and isoprene provided important clues to its possible sources and to the causes of its atmospheric variability. Biomass burning as a source of acetone has been identified for the first time. By using atmospheric data and three-dimensional photochemical models, a global acetone source of 40-60 Tg (=1012 g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons (principally propane, isobutane, and isobutene) provides the single largest source (51%). The remainder is attributable to biomass burning (26%), direct biogenic emissions (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also suggest that acetone photolysis contributed significantly to PAN formation (100-200 ppt) in .the middle and upper troposphere of the sampled region and may be important globally. While the source-sink equation appears to be roughly balanced, much more atmospheric and source data, especially from the southern hemisphere, are needed to reliably quantify the atmospheric budget of acetone. 103 Tg/yr [Duce et al., 1983; Singh and Zimmerman, 1992]. Atmospheric reactions of these NMHCs with ozone (03) and free radicals result in the formation of a variety of intermediate oxygenated species of which carbonyls (RR'C=O) form an important group [National Academy of Sciences (NAS, 1976; Lloyd, 1979; Atkinson, 1990]. There is further evidence that direct emissions of carbonyl species from both natural and manmade sources are also quite common [NAS, 1976; Isidorov et al., 1985; Sigsby et al., 1987]. Carbonyl compounds are of interest to atmospheric chemists because of their potential toxicity, their ability to photolyze and produce free radicals, their ability to form stable atmospheric products, and their interactions in the smog cycles. Because they are frequently intermediate products of atmospheric oxidation, these molecules can serve as excellent tracers for the validation of photochemical models.

Journal of Geophysical Research, 1995

Global Biogeochemical Cycles, 2012

The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is reex... more The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is reexamined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3-dimensional chemistry-transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from 33% to 90% (median of 335%) of total soluble N in rainwater; soluble OP ranges from 20−8320-83% (median of 20−8335%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with 4545% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model-derived present-day soluble ON and OP deposition to the global ocean is estimated to be 4516 Tg-N/yr and 0.35Tg−P/yrrespectivelywithanorderofmagnitudeuncertainty.Oftheseamounts0.35 Tg-P/yr respectively with an order of magnitude uncertainty. Of these amounts 0.35Tg−P/yrrespectivelywithanorderofmagnitudeuncertainty.Oftheseamounts40% and $6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P-limitation in the oligotrophic regions of the world's ocean that rely on atmospheric deposition as an important nutrient source.

Atmospheric Environment, 2013

h i g h l i g h t s Atmospheric N and S depositions over Mediterranean and Black seas are simulat... more h i g h l i g h t s Atmospheric N and S depositions over Mediterranean and Black seas are simulated. N transported from upwind sources is deposited over the Mediterranean. Dry deposition dominates over wet deposition in Mediterranean and Black Sea. Atmospheric N inputs are comparable to N export in Black and W. Mediterranean seas. Atmospheric N input exceeds the N export in the East Mediterranean Sea.

Atmospheric Chemistry and Physics, 2011

Changes in temperature due to variability in meteorology and climate change are expected to signi... more Changes in temperature due to variability in meteorology and climate change are expected to significantly impact atmospheric composition. The Mediterranean is a climate sensitive region and includes megacities like Istanbul and large urban agglomerations such as Athens. The effect of temperature changes on gaseous air pollutant levels and the atmospheric processes that are controlling them in the Eastern Mediterranean are here investigated. The WRF/CMAQ mesoscale modeling system is used, coupled with the MEGAN model for the processing of biogenic volatile organic compound emissions. A set of temperature perturbations (spanning from 1 to 5 K) is applied on a base case simulation corresponding to July 2004. The results indicate that the Eastern Mediterranean basin acts as a reservoir of pollutants and their precursor emissions from large urban agglomerations. During summer, chemistry is a major sink at these urban areas near the surface, and a minor contributor at downwind areas. On average, the atmospheric processes are more effective within the first 1000 m above ground. Temperature increases lead to increases in biogenic emissions by 9 ± 3% K −1. Ozone mixing ratios increase almost linearly with the increases in ambient temperatures by 1±0.1 ppb O 3 K −1 for all studied urban and receptor stations except for Istanbul, where a 0.4±0.1 ppb O 3 K −1 increase is calculated, which is about half of the domain-averaged increase of 0.9 ± 0.1 ppb O 3 K −1. The computed changes in atmospheric processes are also linearly related with temperature changes.

Atmospheric Chemistry and Physics, 2012

Megacities are large urban agglomerations with intensive anthropogenic emissions that have signif... more Megacities are large urban agglomerations with intensive anthropogenic emissions that have significant impacts on local and regional air quality. In the present mesoscale modeling study, the impacts of anthropogenic emissions from the Greater Istanbul Area (GIA) and the Greater Athens Area (GAA) on the air quality in GIA, GAA and the entire East Mediterranean are quantified for typical wintertime (December 2008) and summertime (July 2008) conditions. They are compared to those of the regional anthropogenic and biogenic emissions that are also calculated. Finally, the efficiency of potential country-based emissions mitigation in improving air quality is investigated. The results show that relative contributions from both cities to surface ozone (O 3) and aerosol levels in the cities' extended areas are generally higher in winter than in summer. Anthropogenic emissions from GIA depress surface O 3 in the GIA by ∼ 60 % in winter and ∼ 20 % in summer while those from GAA reduce the surface O 3 in the GAA by 30 % in winter and by 8 % in summer. GIA and GAA anthropogenic emissions contribute to the fine particulate matter (PM 2.5) levels inside the cities themselves by up to 75 % in winter and by 50 % (GIA) and ∼ 40 % (GAA), in summer. GIA anthropogenic emissions have larger impacts on the domain-mean surface O 3 (up to 1 %) and PM 2.5 (4 %) levels compared to GAA anthropogenic emissions (< 1 % for O 3 and ≤ 2 % for PM 2.5) in both seasons. Impacts of regional anthropogenic emissions on the domain-mean surface pollutant levels (up to 17 % for summertime O 3 and 52 % for wintertime fine particulate matter, PM 2.5) are much higher than those from Istanbul and Athens together (∼ 1 % for O 3 and ∼ 6 % for PM 2.5 , respectively). Regional biogenic emissions are found to limit the production of secondary inorganic aerosol species in summer up to 13 % (non-sea-salt sulfate (nss-SO 2− 4) in rural Athens) due to their impact on oxidant levels while they have negligible impact in winter. Finally, the responses to country-based anthropogenic emission mitigation scenarios inside the studied region show increases in O 3 mixing ratios in the urban areas of GIA and GAA, higher in winter (∼ 13 % for GIA and 2 % for GAA) than in summer (∼ 7 % for GIA and < 1 % for GAA). On the opposite PM 2.5 concentrations decrease by up to 30 % in GIA and by 20 % in GAA with the highest improvements computed for winter. The emission reduction strategy also leads to domain-wide decreases in most primary pollutants like carbon monoxide (CO) or nitrogen oxides (NO x) for both seasons. The results show the importance of long range transport of pollutants for the air quality in the East Mediterranean. Thus, improvements of air quality in the East Mediterranean require coordinated efforts inside the region and beyond.

Atmospheric Chemistry and Physics, 2011

Organic acids attract increasing attention as contributors to atmospheric acidity, secondary orga... more Organic acids attract increasing attention as contributors to atmospheric acidity, secondary organic aerosol mass and aerosol hygroscopicity. Oxalic acid is globally the most abundant dicarboxylic acid, formed via chemical oxidation of gas-phase precursors in the aqueous phase of aerosols and droplets. Its lifecycle and atmospheric global distribution remain highly uncertain and are the focus of this study. The first global spatial and temporal distribution of oxalate, simulated using a state-of-the-art aqueous-phase chemical scheme embedded within the global 3-dimensional chemistry/transport model TM4-ECPL, is here presented. The model accounts for comprehensive gas-phase chemistry and its coupling with major aerosol constituents (including secondary organic aerosol). Model results are consistent with ambient observations of oxalate at rural and remote locations (slope = 1.16 ± 0.14, r 2 = 0.36, N =114) and suggest that aqueous-phase chemistry contributes significantly to the global atmospheric burden of secondary organic aerosol. In TM4-ECPL most oxalate is formed in-cloud and less than 5 % is produced in aerosol water.

Atmospheric Chemistry and Physics, 2005

The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance fo... more The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.