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Stratosphere-to-troposphere transport (STT) is an important natural source of tropospheric ozone, which can occasionally influence ground-level ozone concentrations relevant for air quality. Here, we analyse and evaluate the Copernicus Atmosphere Monitoring Service (CAMS) global and regional forecast systems during a deep STT event over Europe for the time period from 4 to 9 January 2017. The predominant synoptic condition is described by a deep upper level trough over eastern and central Europe, favouring the formation of tropopause folding events along the jet stream axis and therefore the intrusion of stratospheric ozone into the troposphere. Both global and regional CAMS forecast products reproduce the hook-shaped streamer of ozone-rich and dry air in the middle troposphere depicted from the observed satellite images of water vapour. The CAMS global model successfully reproduces the folding of the tropopause at various European sites, such as Trapani (Italy), where a deep folding down to 550 hPa is seen. The stratospheric ozone intrusions into the troposphere observed by WOUDC ozonesonde and IAGOS aircraft measurements are satisfactorily forecasted up to 3 days in advance by the CAMS global model in terms of both temporal and vertical features of ozone. The fractional gross error (FGE) of CAMS ozone day 1 forecast between 300 and 500 hPa is 0.13 over Prague, while over Frankfurt it is 0.04 and 0.19, highlighting the contribution of data assimilation, which in most cases improves the model performance. Finally, the meteorological and chemical forcing of CAMS global forecast system in the CAMS regional forecast systems is found to be beneficial for predicting the enhanced ozone concentrations in the middle troposphere during a deep STT event.

In this study we present an evaluation of the Comprehensive Air Quality Model with extensions (CAMx) for Thessaloniki using radiometric and lidar data. The aerosol mass concentration profiles of CAMx are compared against the PM2.5 and PM2. 5−10 concentration profiles retrieved by the Lidar-Radiometer Inversion Code (LIRIC). The CAMx model and the LIRIC algorithm results were compared in terms of mean mass concentration profiles, center of mass and integrated mass concentration in the boundary layer and the free troposphere. The mean mass concentration comparison resulted in profiles within the same order of magnitude and similar vertical structure for the PM2. 5 particles. The mean centers of mass values are also close, with a mean bias of 0.57 km. On the opposite side, there are larger differences for the PM2. 5−10 mode, both in the boundary layer and in the free troposphere. In order to grasp the reasons behind the discrepancies, we investigate the effect of aerosol sources that are not properly included in the model's emission inventory and in the boundary conditions such as the wildfires and the desert dust component. The identification of the cases that are affected by wildfires is performed using wind backward trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model in conjunction with satellite fire pixel data from MODerate-resolution Imaging Spectroradiometer (MODIS) Terra and Aqua global monthly fire location product MCD14ML. By removing those cases the correlation coefficient improves from 0.69 to 0.87 for the PM2. 5 integrated mass in the boundary layer and from 0.72 to 0.89 in the free troposphere. The PM2.5 center of mass fractional bias also decreases to 0.38 km. Concerning the analysis of the desert dust component, the simulations from the Dust Regional Atmospheric Model (BSC-DREAM8b) were deployed. When only the Saharan dust cases are taken into account, BSC-DREAM8b generally outperforms CAMx when compared with LIRIC, achieving a correlation of 0.91 and a mean bias of −29.1 % for the integrated mass in the free troposphere and a correlation of 0.57 for the center of mass. CAMx, on the other hand, underestimates the integrated mass in the free troposphere. Consequently, the accuracy of CAMx is limited concerning the transported Saharan dust cases. We conclude that the performance of CAMx appears to be best for the PM2.5 particles, both in the boundary layer and in the free troposphere. Sources of particles not properly taken into account by the model are confirmed to negatively affect its performance, especially for the PM2. 5−10 particles.

One of the main issues arising from the comparison of ground-based and satellite measurements is the difference in spatial representativeness, which for locations with inhomogeneous spatial distribution of pollutants may lead to significant differences between the two data sets. In order to investigate the spatial variability of tropospheric NO2 within a sub-satellite pixel, a campaign which lasted for about 6 months was held in the greater area of Thessaloniki, Greece. Three multi-axial differential optical absorption spectroscopy (MAX-DOAS) systems performed measurements of tropospheric NO2 columns at different sites representative of urban, suburban and rural conditions. The direct comparison of these ground-based measurements with corresponding products from the Ozone Monitoring Instrument onboard NASA's Aura satellite (OMI/Aura) showed good agreement over the rural and suburban areas, while the comparison with the Global Ozone Monitoring Experiment-2 (GOME-2) onboard EUMETSAT's Meteorological Operational satellites' (MetOp-A and MetOp-B) observations is good only over the rural area. GOME-2A and GOME-2B sensors show an average underestimation of tropospheric NO2 over the urban area of about 10.51 ± 8.32 × 1015 and 10.21 ± 8.87 × 1015 molecules cm−2, respectively. The mean difference between ground-based and OMI observations is significantly lower (6.60 ± 5.71 × 1015 molecules cm−2). The differences found in the comparisons of MAX-DOAS data with the different satellite sensors can be attributed to the higher spatial resolution of OMI, as well as the different overpass times and NO2 retrieval algorithms of the satellites. OMI data were adjusted using factors calculated by an air quality modeling tool, consisting of the Weather Research and Forecasting (WRF) mesoscale meteorological model and the Comprehensive Air Quality Model with Extensions (CAMx) multiscale photochemical transport model. This approach resulted in significant improvement of the comparisons over the urban monitoring site. The average difference of OMI observations from MAX-DOAS measurements was reduced to −1.68 ± 5.01 × 1015 molecules cm−2.

This paper describes the pre-operational analysis and forecasting system developed during MACC (Monitoring Atmospheric Composition and Climate) and continued in the MACC-II (Monitoring Atmospheric Composition and Climate: Interim Implementation) European projects to provide air quality services for the European continent. This system is based on seven state-of-the art models developed and run in Europe (CHIMERE, EMEP, EURAD-IM, LOTOS-EUROS, MATCH, MOCAGE and SILAM). These models are used to calculate multi-model ensemble products. The paper gives an overall picture of its status at the end of MACC-II (summer 2014) and analyses the performance of the multi-model ensemble. The MACC-II system provides daily 96 h forecasts with hourly outputs of 10 chemical species/aerosols (O3, NO2, SO2, CO, PM10, PM2.5, NO, NH3, total NMVOCs (non-methane volatile organic compounds) and PAN+PAN precursors) over eight vertical levels from the surface to 5 km height. The hourly analysis at the surface is done a posteriori for the past day using a selection of representative air quality data from European monitoring stations. The performance of the system is assessed daily, weekly and every 3 months (seasonally) through statistical indicators calculated using the available representative air quality data from European monitoring stations. Results for a case study show the ability of the ensemble median to forecast regional ozone pollution events. The seasonal performances of the individual models and of the multi-model ensemble have been monitored since September 2009 for ozone, NO2 and PM10. The statistical indicators for ozone in summer 2014 show that the ensemble median gives on average the best performances compared to the seven models. There is very little degradation of the scores with the forecast day but there is a marked diurnal cycle, similarly to the individual models, that can be related partly to the prescribed diurnal variations of anthropogenic emissions in the models. During summer 2014, the diurnal ozone maximum is underestimated by the ensemble median by about 4 μg m−3 on average. Locally, during the studied ozone episodes, the maxima from the ensemble median are often lower than observations by 30–50 μg m−3. Overall, ozone scores are generally good with average values for the normalised indicators of 0.14 for the modified normalised mean bias and of 0.30 for the fractional gross error. Tests have also shown that the ensemble median is robust to reduction of ensemble size by one, that is, if predictions are unavailable from one model. Scores are also discussed for PM10 for winter 2013–1014. There is an underestimation of most models leading the ensemble median to a mean bias of −4.5 μg m−3. The ensemble median fractional gross error is larger for PM10 (~ 0.52) than for ozone and the correlation is lower (~ 0.35 for PM10 and ~ 0.54 for ozone). This is related to a larger spread of the seven model scores for PM10 than for ozone linked to different levels of complexity of aerosol representation in the individual models. In parallel, a scientific analysis of the results of the seven models and of the ensemble is also done over the Mediterranean area because of the specificity of its meteorology and emissions. The system is robust in terms of the production availability. Major efforts have been done in MACC-II towards the operationalisation of all its components. Foreseen developments and research for improving its performances are discussed in the conclusion.

This work is an extended evaluation of near-surface ozone as part of the global reanalysis of atmospheric composition, produced within the European-funded project MACC (Monitoring Atmospheric Composition and Climate). It includes an evaluation over the period 2003–2012 and provides an overall assessment of the modeling system performance with respect to near-surface ozone for specific European subregions. Measurements at rural locations from the European Monitoring and Evaluation Program (EMEP) and the European Air Quality Database (AirBase) were used for the evaluation assessment. The fractional gross error of near-surface ozone reanalysis is on average 24 % over Europe, the highest found over Scandinavia (27 %) and the lowest over the Mediterranean marine stations (21 %). Near-surface ozone shows mostly a negative bias in winter and a positive bias during warm months. Assimilation reduces the bias in near-surface ozone in most of the European subregions – with the exception of Britain and Ireland and the Iberian Peninsula and its impact is mostly notable in winter. With respect to the seasonal cycle, the MACC reanalysis reproduces the photochemically driven broad spring-summer maximum of surface ozone of central and south Europe. However, it does not capture adequately the early spring peak and the shape of the seasonality at northern and north-eastern Europe. The diurnal range of surface ozone, which is as an indication of the local photochemical production processes, is reproduced fairly well, with a tendency for a small overestimation during the warm months for most subregions (especially in central and southern Europe). Possible reasons leading to discrepancies between the MACC reanalysis and observations are discussed.

Daily global analyses and 5-day forecasts are generated in the context of the European Monitoring Atmospheric Composition and Climate (MACC) project using an extended version of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The IFS now includes modules for chemistry, deposition and emission of reactive gases, aerosols, and greenhouse gases, and the 4-dimensional variational data assimilation scheme makes use of multiple satellite observations of atmospheric composition in addition to meteorological observations. This paper describes the data assimilation setup of the new Composition-IFS (C-IFS) with respect to reactive gases and validates analysis fields of ozone (O3), carbon monoxide (CO), and nitrogen dioxide (NO2) for the year 2008 against independent observations and a control run without data assimilation. The largest improvement in CO by assimilation of Measurements of Pollution in the Troposphere (MOPITT) CO columns is seen in the lower troposphere of the Northern Hemisphere (NH) extratropics during winter, and during the South African biomass-burning season. The assimilation of several O3 total column and stratospheric profile retrievals greatly improves the total column, stratospheric and upper tropospheric O3 analysis fields relative to the control run. The impact on lower tropospheric ozone, which comes from the residual of the total column and stratospheric profile O3 data, is smaller, but nevertheless there is some improvement particularly in the NH during winter and spring. The impact of the assimilation of tropospheric NO2 columns from the Ozone Monitoring Instrument (OMI) is small because of the short lifetime of NO2, suggesting that NO2 observations would be better used to adjust emissions instead of initial conditions. The results further indicate that the quality of the tropospheric analyses and of the stratospheric ozone analysis obtained with the C-IFS system has improved compared to the previous "coupled" model system of MACC.

The urban heat island (UHI) effect is one prominent form of localized anthropogenic climate modification. It represents a significant urban climate problem since it occurs in the layer of the atmosphere where almost all daily human activities take place. This paper presents the development of a high-resolution modeling system that could be used for simulating the UHI effect in the context of operational weather forecasting activities. The modeling system is built around a state-of-the-art numerical weather prediction model, properly modified to allow for the better representation of the urban climate. The model performance in terms of simulating the near-surface air temperature and thermal comfort conditions over the complex urban area of Athens, Greece, is evaluated during a 1.5-month operational implementation in the summer of 2010. Results from this case study reveal an overall satisfactory performance of the modeling system. The discussion of the results highlights the important role that, given the necessary modifications, a meteorological model can play as a supporting tool for developing successful heat island mitigation strategies. This is further underlined through the operational character of the presented modeling system.

A detailed 3-D evaluation of an ensemble of five regional Chemistry Transport Models (RCTM) and one global CTM with focus on free tropospheric ozone over Europe is presented. It is performed over a summer period (June to August 2008) in the context of the GEMS-RAQ project. A data set of about 400 vertical ozone profiles from balloon soundings and commercial aircraft at 11 different locations is used for model evaluation, in addition to satellite measurements with the infrared nadir sounder (IASI) showing largest sensitivity to free tropospheric ozone. In the middle troposphere, the four regional models using the same top and boundary conditions from IFS-MOZART exhibit a systematic negative bias with respect to observed profiles of about −20%. Root Mean Square Error (RMSE) values are constantly growing with altitude, from 22% to 32% to 53%, respectively for 0–2 km, 2–8 km and 8–10 km height ranges. Lowest correlation is found in the middle troposphere, with minimum coefficients (R) between 0.2 to 0.45 near 8 km, as compared to 0.7 near the surface and similar values around 10 km. A sensitivity test made with the CHIMERE mode also shows that using hourly instead of monthly chemical boundary conditions generally improves the model skill (i.e. improve RMSE and correlation). Lower tropospheric 0–6 km partial ozone columns derived from IASI show a clear North-South gradient over Europe, which is qualitatively reproduced by the models. Also the temporal variability showing decreasing ozone concentrations in the lower troposphere (0–6 km columns) during summer is well reproduced by models even if systematic bias remains (the value of the bias being also controlled by the type of used boundary conditions). A multi-day case study of a trough with low tropopause was conducted and showed that both IASI and models were able to resolve strong horizontal gradients of middle and upper tropospheric ozone occurring in the vicinity of an upper tropospheric frontal zone.

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 O3 K−1 for all studied urban and receptor stations except for Istanbul, where a 0.4±0.1 ppb O3 K−1 increase is calculated, which is about half of the domain-averaged increase of 0.9±0.1 ppb O3 K−1. The computed changes in atmospheric processes are also linearly related with temperature changes.

Regional climate-air quality decadal simulations over Europe were carried out with the RegCM3/CAMx modeling system for the time slice 1991–2000, in order to study the impact of different meteorological forcing on surface ozone. The RegCM3 regional climate model was firstly constrained by the ERA40 reanalysis dataset which is considered as an experiment with perfect meteorological boundary conditions and then it was constrained by the global circulation model ECHAM5. A number of meteorological parameters were examined including the 500 mb geopotential height, solar radiation, temperature, cloud liquid water path, planetary boundary layer height and surface wind. The different RegCM meteorological forcing resulted in changes of near surface ozone over Europe ranging between ± 4 ppb for winter and summer. The area showing the greatest sensitivity in O3 during winter is central and southern Europe while in summer central north continental Europe. The different meteorological forcing impacts on the atmospheric circulation, which in turn affects cloudiness and solar radiation, temperature, wind patterns and the meteorology depended biogenic emissions. For comparison reasons, the impact of chemical boundary conditions on surface ozone was additionally examined with a series of sensitivity studies, indicating that surface ozone changes are comparable to those caused by the different meteorological forcing. These findings suggest that, when it comes to regional climate-air quality simulations, the selection of external meteorological forcing can be as important as the selection of adequate chemical lateral boundary conditions.

High frequency of agricultural fires is observed every year during the summer months over SW Russia and Eastern Europe. This study investigates the initial injection height of aerosol generated by the fires over these regions during the biomass burning season, which determines the potential for long-range transport of the smoke. This information is critical for aerosol transport modeling, as it determines the smoke plume evolution. The study focuses on the period 2006–2008, and is based on observations made by the CALIOP instrument on board the NASA CALIPSO satellite. MODIS data are synergistically used for the detection of the fires and the characterization of their intensity. CALIPSO aerosol vertical distributions generated by the active fires are analyzed to investigate the aerosol top height which is considered dependent on the heat generated by the fires and can be associated with the initial injection height. Aerosol top heights of the vertically homogenous smoke layers are found to range between 1.6 and 5.9 km. Smoke injection heights from CALIPSO are compared with mixing layer heights taken by the European Centre for Medium-range Weather Forecast (ECMWF), to investigate the direct injection of smoke particles into the free troposphere. Our results indicate that the aerosol plumes are observed within the boundary layer for the 50% of the cases examined. For the rest of the cases, the strong updrafts generated by the fires resulted to smoke injection heights greater than the ECMWF estimated mixing layer by 0.5 to 3.0 km, indicating a direct smoke injection into the free troposphere. The smoke injection height showed a dependence on the MODIS-Land Fire Radiative Power product which is indicative of the fire intensity, especially in the cases of lower static stability in the upper part of the boundary layer and the free troposphere.

We present a comparison of tropospheric NO2 from OMI measurements to the median of an ensemble of Regional Air Quality (RAQ) models, and an intercomparison of the contributing RAQ models and two global models for the period July 2008–June 2009 over Europe. The model forecasts were produced routinely on a daily basis in the context of the European GEMS ("Global and regional Earth-system (atmosphere) Monitoring using Satellite and in-situ data") project. The tropospheric vertical column of the RAQ ensemble median shows a spatial distribution which agrees well with the OMI NO2 observations, with a correlation r=0.8. This is higher than the correlations from any one of the individual RAQ models, which supports the use of a model ensemble approach for regional air pollution forecasting. The global models show high correlations compared to OMI, but with significantly less spatial detail, due to their coarser resolution. Deviations in the tropospheric NO2 columns of individual RAQ models from the mean were in the range of 20–34% in winter and 40–62% in summer, suggesting that the RAQ ensemble prediction is relatively more uncertain in the summer months. The ensemble median shows a stronger seasonal cycle of NO2 columns than OMI, and the ensemble is on average 50% below the OMI observations in summer, whereas in winter the bias is small. On the other hand the ensemble median shows a somewhat weaker seasonal cycle than NO2 surface observations from the Dutch Air Quality Network, and on average a negative bias of 14%. Full profile information was available for two RAQ models and for the global models. For these models the retrieval averaging kernel was applied. Minor differences are found for area-averaged model columns with and without applying the kernel, which shows that the impact of replacing the a priori profiles by the RAQ model profiles is on average small. However, the contrast between major hotspots and rural areas is stronger for the direct modeled vertical columns than the columns where the averaging kernels are applied, related to a larger relative contribution of the free troposphere and the coarse horizontal resolution in the a priori profiles compared to the RAQ models. In line with validation results reported in the literature, summertime concentrations in the lowermost boundary layer in the a priori profiles from the DOMINO product are significantly larger than the RAQ model concentrations and surface observations over the Netherlands. This affects the profile shape, and contributes to a high bias in OMI tropospheric columns over polluted regions. The global models indicate that the upper troposphere may contribute significantly to the total column and it is important to account for this in comparisons with RAQ models. A combination of upper troposphere model biases, the a priori profile effects and DOMINO product retrieval issues could explain the discrepancy observed between the OMI observations and the ensemble median in summer.

Satellite observations of nitrogen dioxide (NO2) tropospheric columns over south-eastern Europe are analyzed to study the characteristics of the spatial and temporal variability of pollution in the area. The interannual variability of the tropospheric NO2 columns is presented over urban, rural and industrial locations based on measurements from four satellite instruments, GOME/ERS-2, SCIAMACHY/Envisat, OMI/Aura and GOME-2/MetOp spanning a period of over twelve years. The consistency between the different datasets over the area is investigated. Two operational algorithms for the retrieval of tropospheric NO2 are considered, the one developed jointly by the Royal Netherlands Meteorological Institute and Belgian Institute for Space Astronomy and the one developed by the University of Bremen. The tropospheric NO2 columns for the area under study have been simulated for the period 1996–2001 with the Comprehensive Air Quality Model (CAMx) and are compared with GOME measurements. Over urban and industrial locations the mean tropospheric NO2 columns range between 3 and 7.0×1015 molecules/cm2, showing a seasonal variability with a peak to peak amplitude of about 6.0×1015 molecules/cm2, while the background values over rural sites are close to 1.1×1015 molecules/cm2. Differences in the overpass time and spatial resolution of the different satellites, as well as differences in the algorithms, introduce significant differences in the estimated columns however the correlation between the different estimates is higher than 0.8. It is found that the model simulations reveal similar spatial patterns as the GOME observations, a result which is consistent with both algorithms. Although the model simulations show a mean bias of −0.1×1015 molecules/cm2 under clean conditions, the modeled temporal correlation of 0.5 is poor in absence of biogenic and biomass burning emissions.

This study investigates the effects of the total solar eclipse of 29 March 2006 on surface air-quality levels over Greece based on observations at a number of sites in conjunction with chemical box modelling and 3-D air-quality modelling. Emphasis is given on surface ozone and other photooxidants at four Greek sites Kastelorizo, Finokalia (Crete), Pallini (Athens) and Thessaloniki, which are located at gradually increasing distances from the path of the eclipse totality and are characterized by different air pollution levels. The eclipse offered the opportunity to test our understanding of air pollution build-up and the response of the gas-phase chemistry of photo-oxidants during a photolytical perturbation using both a photochemical box model and a regional air-quality offline model based on the modeling system WRF/CAMx. At the relatively unpolluted sites of Kastelorizo and Finokalia no clear signal of the solar eclipse on surface O3, NO2 and NO concentrations can be deduced from the observations while there is no correlation of observed O3, NO2 and NO with observed global radiation. The box and regional model simulations for the two relatively unpolluted sites indicate that the calculated changes in net ozone production rates between eclipse and non eclipse conditions are rather small compared to the observed short-term ozone variability. Furthermore the simulated ozone lifetime is in the range of a few days at these sites and hence the solar eclipse effects on ozone can be easily masked by local and regional transport. At the polluted sites of Thessaloniki and Pallini, the solar eclipse effects on O3, NO2 and NO concentrations are revealed from both the measurements and modeling with the net effect being a decrease in O3 and NO and an increase in NO2 as NO2 formed from the reaction of O3 with NO while at the same time NO2 is not efficiently photolysed. This result is also supported by a positive correlation of observed global radiation with O3 and NO and a negative correlation with NO2. It is evident from the 3-D air quality modeling over Greece that the maximum effects of the eclipse on O3, NO2 and NO are reflected on the large urban agglomerations of Athens, and Thessaloniki where the maximum of the emissions occur.

An investigation of the Planetary Boundary Layer (PBL) height evolution over Greece, during the solar eclipse of 29 March 2006, is presented. Ground based observations were carried out using lidar detection and ranging devices and ground meteorological instruments, to estimate the height of the mixing layer (ML) before, during and after the solar eclipse in northern and southern parts of Greece exhibiting different sun obscuration. Data demonstrate that the solar eclipse has induced a decrease of the PBL height, indicating a suppression of turbulence activity similar to that during the sunset hours. The changes in PBL height were associated with a very shallow entrainment zone, indicating a significant weakening of the penetrative convection. Heat transfer was confined to a thinner layer above the ground. The thickness of the entrainment zone exhibited its minimum during the maximum of the eclipse, demonstrative of turbulence mechanisms suppression at that time. Model estimations of the PBL evolution were additionally conducted using the Comprehensive Air Quality Model with extensions (CAMx) coupled with the Weather Research and Forecasting model (WRF). Model-diagnosed PBL height decrease during the solar eclipse due to vertical transport decay, in agreement with the experimental findings; vertical profiles of atmospheric particles and gaseous species showed an important vertical mixing attenuation.

This paper examines the effect of the total solar eclipse of 29 March 2006 on meteorological variables across Greece. Integrated micrometeorological measurements were conducted at Kastelorizo, a small island within the path of totality, and other sites within the Greek domain, with various degrees of solar obscuration. The observations showed a dramatic reduction in the incoming global radiation and subsequent, pronounced changes in surface air temperature with the lowest temperature values occurring about 15 min after the full phase. The amplitude of the air temperature drop was not analogous to the obscuration percentage but was principally determined by the surrounding environment (mainly the sea influence), the background meteorological conditions and local cloudiness. Surface wind-speed decreased in most sites as a result of the cooling and stabilization of the atmospheric boundary layer. This perturbation provided a unique opportunity to apply a sensitivity analysis on the effect of the eclipse to the Weather Research and Forecast (WRF) numerical mesoscale meteorological model. Strong anomalies, not associated with a dynamic response, were simulated over land especially in surface air temperature. The simulated temperature drop pattern was consistent with the observations.

Aerosol levels at Mediterranean Basin are significantly affected by desert dust that is eroded in North Africa and is transported northwards. This study aims to assess the performance of the Dust REgional Atmospheric Model (BSC-DREAM8b) in the prediction of dust outbreaks near the surface in Eastern Mediterranean. For this purpose, model PM10 predictions covering a 7-year period and PM10 observations at five surface monitoring sites in Greece are used. A quantitative criterion is set to select the significant dust outbreaks defined as those when the predicted PM10 surface concentration exceeds 12 μg/m3. The analysis reveals that significant dust transport is usually observed for 1–3 consecutive days. Dust outbreak seasons are spring and summer, while some events are also forecasted in autumn. The seasonal variability of dust transport events is different at Finokalia, where the majority of events are observed in spring and winter. Dust contributes by 19–25% to the near surface observed PM10 levels, which can be increased to more than 50 μg/m3 during dust outbreaks, inducing violations of the air quality standards. Dust regional modeling can be regarded as a useful tool for air quality managers when assessing compliance with air quality limit values.

The deterministic approach of sensitivity analysis is applied on the solution vector of an Air Quality Model. In particular, the photochemical CAMx code is augmented with derivatives utilising the automatic differentiation software ADIFOR. The enhanced with derivatives version of the model is then adopted in a study of the effect of perturbations at the boundary conditions on the predicted ozone concentrations. The calculated derivative matrix provides valuable information e.g., on the ordering of the infl uential factors or the localisation of highly affected regions. Two fundamentally different domains of the Auto-Oil II programme were used as test cases for the simulations, namely Athens and Milan. The results suggest that ozone concentration be highly affected by its own boundary conditions and subsequently, with an order of magnitude less, by the boundary conditions of NOX and VOC.

No abstract available.

Using daily data, we investigate the relationship between European LNG prices, carbon prices (CO2), electricity wholesale prices and changes in the electricity sector’s energy mix in Greece, using a vector error correction model (VECM). The results indicate that an increase in the daily average price of natural gas has the expected impact on Greece’s wholesale electricity price. As expected, gas and other fossil fuels act as substitute goods, while higher imports of electricity lower prices and have a negative impact on fossil fuel shares. Interestingly, carbon prices do not appear to have any significant impact on any variables, while the higher production of electricity from renewable sources pushes wholesale electricity prices down.

We explore, for the first time in the literature, how the revenues of ship management companies respond to macroeconomic exogenous shocks. Using data for ship-management companies in Cyprus, we find evidence that a demand shock has the largest impact on revenues, exhibiting an almost one-for-one relationship. If the demand shock is permanent, we observe a ceteris paribus permanent effect on revenues. Similarly, this occurs irrespective of the final effect that demand has on the relevant freight rate, proxied via the Baltic dry and tanker (dirty and clean) indices. The BDI and the BDTI indices have a smaller effect on revenues, standing at approximately 0.05% for every 1% shock, while the clean tanker index does not have an effect, most likely due to their fleet composition. In accordance with the literature, we find that a shock in the price of Brent oil increases revenues. Our results bear importance not only for ship management companies per se, but also for countries that are ship management hubs.

We estimate intentional and unintentional herding in the dry-bulk, ocean-going segment that spans from August 1998 to January 2020 and measure how this can impact vessel orders. As the results suggest, while intentional herding has a large effect on the orders of the newbuilding vessels, the impact is very short-lived. On the contrary, unintentional herding, related to common environmental factors, has a smoother but more time persistent effect on the newbuilding vessels. The findings suggest that the key players in the market do not only affect the dry-bulk market with their decisions but also the logistics trade and ultimately the world economy. Thus, the inclusion of the dry bulk key shipowners by the policymakers in the discussions before reaching an important decision could minimise the volatility of the overall sector.

We investigate and quantify the relationship between agricultural commodities and ocean-going freight rates, using a weekly dataset from 2010 to 2019 and a Vector Error Correction Methodology. The results are firstly supportive of the view that vessel classes are highly interconnected, and secondly confirm that commodity prices can have a strong impact on freight rates across most vessel classes. For commodities in which no impact is registered on freight rates, the possibility of substitution effects exists. Furthermore, the results indicate that the markets in which these products trade can be a significant determinant of future freight rate movements. These findings can be particularly useful for agricultural businesses that are concerned with the transportation cost of their products and the ways that the latter can be mitigated.

The latest generation of heavy-duty vehicles (Euro VI step E) have to respect low emission limits both in the laboratory and on the road. The most challenging pollutants for diesel vehicles are NOx and particles; nevertheless, NH3 and N2O need attention. In this study, we measured regulated and unregulated pollutants of a Euro VI step E Diesel vehicle. Samples were taken downstream of (i) the engine, (ii) the Diesel oxidation catalyst (DOC) and catalyzed Diesel particulate filter (cDPF), and (iii) the selective catalytic reduction (SCR) unit for NOx with an ammonia slip catalyst (ASC). In addition to typical laboratory and real-world cycles, various challenging tests were conducted (urban driving with low payload, high-speed full-load driving, and idling) at 23 °C and 5 °C. The results showed high efficiencies of the DOC, DPF, and SCR under most testing conditions. Cold start cycles resulted in high NOx emissions, while high-temperature cycles resulted in high particle emissions. The main message of this study is that further improvements are necessary, also considering possible reductions in the emission limits in future EU regulations.

Formaldehyde (HCHO), a carcinogenic carbonyl compound and precursor of tropospheric ozone, can be found in vehicle exhaust. Even though the continuous monitoring of HCHO has been recommended, the real-world emissions from the road transport sector are not commonly available. The main reason for this knowledge gap has been the difficulty to measure HCHO in real-time and during real-world testing. This, for instance, increases the uncertainty of the O3 simulated by air quality models. The present study investigates real-time HCHO measurements comparing three Fourier Transform InfraRed spectrometers (FTIRs) and one Quantum Cascade Laser InfraRed spectrometer (QCL-IR) directly sampling from the exhaust of one gasoline passenger car, one Diesel commercial vehicle and one Diesel heavy-duty vehicle, all meeting recent European emission standards (Euro 6/VI). Non-negligible emissions of HCHO were measured from the Diesel light-duty vehicle, with emissions increasing as temperature decreased. Relatively low emissions were measured for the gasoline car and the Diesel heavy-duty vehicle. The results showed a good correlation between the different instruments under all the conditions tested (in most cases R2 > 0.9). Moreover, it was shown that HCHO can be accurately measured during on-road and real-world-like tests using instruments based on FTIR and QCL-IR technologies.

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives in Europe. Most studies on emissions factors are based on old technology CNG and LPG fueled vehicles. Furthermore, there are not many data at low ambient temperatures, on-road driving, or unregulated pollutants, such as ammonia (NH3). In this study we measured the emissions of one Euro 6b CNG light commercial vehicle, one Euro 6b and one Euro 6d-Temp bi-fuel LPG passenger car, one Euro 6d-Temp bi-fuel CNG passenger car, and four Euro 6d-Temp CNG passenger cars. Tests included on-road testing and worldwide harmonized light vehicles test cycles (WLTC) in the laboratory with cold and hot engine, at 23 °C and −7 °C. The results showed 10–23% CO2 savings in gas modality compared to gasoline, lower CO and particle number emissions, and relatively similar total and non-methane hydrocarbons and NOx emissions. The ammonia emissions were high for all vehicles and fuels; higher than gasoline and diesel vehicles. The results also showed that, following the introduction of the real-driving emissions regulation, even though not applicable to the examined vehicles, Euro 6d-Temp vehicles had lower emissions compared to the Euro 6b vehicles.

We employ a Bayesian Vector Autoregressive methodology, to counter the issue of data availability, and explore the relationship between seaborne commodity trade and freight rates. Our results show three important insights: first and foremost, the quantity of seaborne commodity trade has a strong impact on the Baltic Dry Index and the Baltic Dirty Tanker Index, but not on the Baltic Clean Tanker Index, most likely due to the fact that clean tankers can simultaneously operate both in the clean and the dirty sectors. Second, a shock in the price of brent oil has the expected positive response from the Baltic Dry Index, while its relationship with the Baltic Clean Tanker Index and the Baltic Dirty Tanker Index is negative as, in this case, tanker vessels can operate as floating storage units. Third, a relationship between the freight indices appears to hold as a change in one could spill over to the other.

This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH3 and N2O. The NOx, N2O, and NH3 emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH3 and N2O is observed in both Diesel and gasoline light-duty vehicles, whereby NH3 emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH3 emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N2O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles.