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Land–atmosphere interactions govern the process of dust emission and transport. An accurate depiction of these physical processes within numerical weather prediction models allows for better estimating the spatial and temporal distribution of the dust burden and the characterisation of source and recipient areas. In the presented study, the ECMWF-IFS (European Centre for Medium-Range Weather Forecast – Integrated Forecasting System) outputs, produced with and without the assimilation of Aeolus quality-assured Rayleigh–clear and Mie–cloudy horizontal line-of-sight wind profiles, are used as initial or boundary conditions in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate 2-month periods in the spring and autumn of 2020, focusing on a case study in October. The experiments have been performed over the broader eastern Mediterranean and Middle East (EMME) region, which is frequently subjected to dust transport, as it encompasses some of the most active erodible dust sources. Aerosol- and dust-related model outputs (extinction coefficient, optical depth and concentrations) are qualitatively and quantitatively evaluated against ground- and satellite-based observations. Ground-based columnar and vertically resolved aerosol optical properties are acquired through AERONET sun photometers and PollyXT lidar, while near-surface concentrations are taken from EMEP. Satellite-derived vertical dust and columnar aerosol optical properties are acquired through LIVAS (LIdar climatology of Vertical Aerosol Structure) and MIDAS (ModIs Dust AeroSol), respectively. Overall, in cases of either high or low aerosol loadings, the model predictive skill is improved when WRF-Chem simulations are initialised with the meteorological fields of Aeolus wind profiles assimilated by the IFS. The improvement varies in space and time, with the most significant impact observed during the autumn months in the study region. Comparison with observation datasets saw a remarkable improvement in columnar aerosol optical depths, vertically resolved dust mass concentrations and near-surface particulate concentrations in the assimilated run against the control run. Reductions in model biases, either positive or negative, and an increase in the correlation between simulated and observed values was achieved for October 2020.

Mineral dust and sea spray aerosol represent important sources of ice-nucleating particles (INPs), the minor fraction of aerosol particles able to trigger cloud ice crystal formation and, consequently, influence multiple climate-relevant cloud properties including lifetime, radiative properties and precipitation initiation efficiency. Mineral dust is considered the dominant INP source in many parts of the world due to its ice nucleation efficiency and its sheer abundance, with global emission rates of up to 4700 Tg a−1. However, INPs emitted from the ocean surface in sea spray aerosol frequently dominate INP populations in remote marine environments, including parts of the Southern Ocean where cloud-resolving model simulations have demonstrated that cloud radiative properties are likely strongly controlled by INPs. Here we report INP concentrations measured in aerosol and seawater samples during Air Quality and Climate Change in the Arabian Basin (AQABA), a shipborne campaign that spanned the Red Sea, Gulf of Aden, Arabian Sea, Arabian Gulf and part of the Mediterranean. In aerosol samples collected within a few hundred kilometers of the first and second ranked sources of dust globally, the Sahara and Arabian Peninsula, INP concentrations ranged from 0.2 to 11 L−1 at −20 ∘C with observed ice-active surface site densities (ns) 1–3 orders of magnitude below levels predicted by mineral dust INP parameterizations. Over half of the samples (at least 14 of 26) were collected during dust storms with average dust mass concentrations between 150 and 490 µg m−3 (PM10), as simulated by the Modern-Era Retrospective analysis for Research and Application, version 2 (MERRA-2). The impacts of heat and peroxide treatments indicate that organics dominated the observed ice nucleation (IN) activity at temperatures ≥ −15 ∘C with proteinaceous (heat-labile) INPs frequently observed at high freezing temperatures >−10 ∘C. INP concentrations in seawater samples ranged between 3 and 46 mL−1 at −19 ∘C, demonstrating the relatively low INP source potential of seawater in the region as compared to seawater from multiple other regions reported previously. Overall, our results demonstrate that despite proximity to the Sahara and the Arabian Peninsula and the dominance of mineral dust in the aerosol sampled, existing mineral dust parameterizations alone would not skillfully represent the near-surface ns in the observed temperature regime (−6 to −25 ∘C). Future efforts to develop or improve representations of dust INPs at modest supercooling (≥-15 ∘C) would benefit from a characterization of the specific organic species associated with dust INPs. More generally, an improved understanding of the organic species associated with increased IN activity and their variability across dust source regions would directly inform efforts to determine whether ns-based parameterizations are appropriate for faithful representation of dust INPs in this sensitive temperature regime, whether region-specific parameterizations are required, or whether an alternative to the ns approach is necessary.

Urban areas and industrial facilities, which concentrate the majority of human activity and industrial production, are major sources of air pollutants, with serious implications for human health and global climate. For most of these pollutants, emission inventories are often highly uncertain, especially in developing countries. Spaceborne measurements from the TROPOMI instrument, on board the Sentinel-5 Precursor satellite, are used to retrieve nitrogen dioxide (NO2) column densities at high spatial resolution. Here, we use 2 years of TROPOMI retrievals to map nitrogen oxide (NOx = NO + NO2) emissions in Egypt with a top-down approach using the continuity equation in steady state. Emissions are expressed as the sum of a transport term and a sink term representing the three-body reaction comprising NO2 and hydroxyl radical (OH). This sink term requires information on the lifetime of NO2, which is calculated with the use of the CAMS near-real-time temperature and OH concentration fields. We compare this derived lifetime with the lifetime inferred from the fitting of NO2 line density profiles in large plumes with an exponentially modified Gaussian function. This comparison, which is conducted for different samples of NO2 patterns above the city of Riyadh, provides information on the reliability of the CAMS near-real-time OH concentration fields; it also provides some hint on the vertical levels that best represent typical pollution sources in industrial areas and megacities in the Middle East region. In Egypt, total emissions of NOx are dominated by the sink term, but they can be locally dominated by wind transport, especially along the Nile where human activities are concentrated. Megacities and industrial regions clearly appear as the largest sources of NOx emissions in the country. Our top-down model infers emissions with a marked annual variability. By looking at the spatial distribution of emissions at the scale of different cities with different industrial characteristics, it appears that this variability is consistent with national electricity consumption. We detect lower emissions on Fridays, which are inherent to the social norm of the country, and quantify the drop in emissions in 2020 due to the COVID-19 pandemic. Overall, our estimations of NOx emissions for Egypt are 7.0 % higher than the CAMS-GLOB-ANT_v4.2 inventory and significantly differ in terms of seasonality.

Unmanned aerial vehicles (UAVs) provide a cost-effective way to fill in gaps between surface in situ observations and remotely sensed data from space. In this study, a novel portable CO2 measuring system suitable for operations on board small-sized UAVs has been developed and validated. It is based on a low-cost commercial nondispersive near-infrared (NDIR) CO2 sensor (Senseair AB, Sweden), with a total weight of 1058 g, including batteries. The system performs in situ measurements autonomously, allowing for its integration into various platforms. Accuracy and linearity tests in the lab showed that the precision remains within ± 1 ppm (1σ) at 1 Hz. Corrections due to temperature and pressure changes were applied following environmental chamber experiments. The accuracy of the system in the field was validated against a reference instrument (Picarro, USA) on board a piloted aircraft and it was found to be ± 2 ppm (1σ) at 1 Hz and ± 1 ppm (1σ) at 1 min. Due to its fast response, the system has the capacity to measure CO2 mole fraction changes at 1 Hz, thus allowing the monitoring of CO2 emission plumes and of the characteristics of their spatial and temporal distribution. Details of the measurement system and field implementations are described to support future UAV platform applications for atmospheric trace gas measurements.

The geographical origin and source apportionment of submicron carbonaceous aerosols (organic aerosols, OAs, and black carbon, BC) have been investigated here for the first time, deploying high time-resolution measurements at an urban background site of Nicosia, the capital city of Cyprus, in the eastern Mediterranean. This study covers a half-year period, encompassing both the cold and warm periods with continuous observations of the physical and chemical properties of PM1 performed with an Aerosol Chemical Speciation Monitor (ACSM), an aethalometer, accompanied by a suite of various ancillary offline and online measurements. Carbonaceous aerosols were dominant during both seasons (cold and warm periods), with a contribution of 57 % and 48 % to PM1, respectively, and exhibited recurrent intense nighttime peaks (> 20–30 µg m−3) during the cold period, associated with local domestic heating. The findings of this study show that high concentrations of sulfate (close to 3 µg m−3) were continuously recorded, standing among the highest ever reported for Europe and originating from the Middle East region. Source apportionment of the OA and BC fractions was performed using the positive matrix factorization (PMF) approach and the combination of two models (aethalometer model and multilinear regression), respectively. Our study revealed elevated hydrocarbon-like organic aerosol (HOA) concentrations in Nicosia (among the highest reported for a European urban background site), originating from a mixture of local and regional fossil fuel combustion sources. Although air masses from the Middle East had a low occurrence and were observed mostly during the cold period, they were shown to strongly affect the mean concentrations levels of BC and OA in Nicosia during both seasons. Overall, the present study brings to our attention the need to further characterize primary and secondary carbonaceous aerosols in the Middle East, an undersampled region characterized by continuously increasing fossil fuel (oil and gas) emissions and extreme environmental conditions, which can contribute to photochemical ageing.

The ADRIMED campaign provides measurements of all key parameters regarding atmospheric composition in the Mediterranean area during the summer 2013. This is an opportunity to quantify the ability of current models to adequately represent the atmospheric composition in this complex region, which is influenced by anthropogenic emissions from Europe, Africa, the Middle-East and from shipping activities as well as mineral dust emissions mostly from the arid areas in Africa, sea-salt emissions, biomass burning emissions and biogenic emissions from the vegetation. The CHIMERE model in its present version is a chemistry-transport model which takes into account all these processes. We show here by simulating the period from 5 June to 15 July 2013 with the CHIMERE model and comparing the results to both routine and specific ADRIMED measurements that this model allows an adequate representation the atmospheric composition over the western Mediterranean, in terms of ozone concentration, particulate matter (PM) and aerosol optical depth (AOD). It is also shown that the concentrations of PM on all the considered area is dominated by mineral dust, even though local dust emissions in Europe are certainly overestimated by the model. A comparison with sulphate concentrations at Cape Corsica exhibits some discrepancies related to the regridding of shipping emissions.

Urban areas and industrial facilities are major sources of air pollutants, as they concentrate a large part of human activity and industrial production. For most of these pollutants, emission inventories are highly uncertain, especially in developing countries. In this context, satellite observations can be used to observe column densities of chemical species to reduce uncertainties in inventories. Here, we use three years of TROPOMI daily nitrogen dioxide (NO2) retrievals to map nitrogen oxide (NOx) emissions at high resolution in Egypt, Qatar and Cyprus. We use a flux-divergence scheme, which expresses NOx emissions as the sum of a wind transport term and a chemical sink term representing the reaction between NO2 and hydroxyl radical (OH). The model allows to identify major NOx hotspots. Among these, heavy industrial facilities, such as cement plants and fossil-fuel fired power plants, are characterized by a predominance of the transport term over the sink term. Heavily populated urban centers can also be identified, with a predominance of the sink term. In Egypt, our model is able to detect a weekly cycle in NOx emissions, reflecting Egyptian social norms, and to quantify the drop of emissions in 2020 due to the Covid-19 pandemic. In Qatar, it is able to infer the emission factor of isolated power plants, which is consistent with reported values. In Cyprus, it is able to quantify the emissions from different power plants, with higher emissions on the north side of the island due to the use of different technologies and fuels. These results demonstrate a high potential for satellite-based emission mapping at the scale of large urbanised areas well observed by TROPOMI.

During June 2022, the Cyprus Institute (CyI) took part in the ASKOS experiment in Mindelo, Cape Verde, with several of Unmanned Aerial Vehicles (UAVs), fitted with a number of in-situ aerosol instruments able to profile the Saharan Air Layer between the surface and an altitude of 5,300 m. In addition to ASKOS objectives, transnational access project Diurnal vAriation of the vertically resolved siZe distribution in the Saharan Air Layer (DAZSAL) was also carried out at the same time. The campaign aimed at validating the Aeolus L2A product in the presence of dust and marine aerosols, estimating the influence on Aeolus products of non-spherical particles, evaluating the impact of particle orientation, and study the diurnal cycle of the dust size-distribution at high altitude. In this presentation we will present and discuss the scientific objectives, the context, the Unmanned Aerial Systems (UASs) that we developed in-house, and the instruments used, together with their limitations, calibration methods, uncertainties, challenges and difficulties encountered. We will also discuss the logistical and planning challenges that such a campaign entails.Operations took place from the Cesaria Evora International Airport. The instruments deployed on-board the UAVs permitted to evaluate the height-resolved particle size-distribution between 0.1 and 40 µm and detect cases of particle orientation, to complement the observations with ground-based remote sensing set out by NOA and TROPOS. Moreover, 24 high-altitude dust samples were collected on impactors, for further analysis by Scanning Electron Microscopy. In total, 25 scientific flights were performed on 12 flying days (almost half of which at night). Five flights were conducted during Aeolus overpasses. Weather has been a determining factor for both the ground-based remote sensing operations and the UAS operation, and airport traffic has been another constraint that needed to be accounted for, in the UAS operation.

Methane (CH4) is a potent greenhouse gas but its sources remain poorly quantified in the Eastern Mediterranean and Middle East (EMME) region where major oil and gas production takes place. Light alkanes, such as ethane (C2H6), are co-emitted with CH4 by oil and gas activities and are promising tracers for quantifying the methane emissions from this sector. Cyprus is an ideal location for studying the composition of regional air masses and for characterizing different emission source signatures at a regional scale. A Picarro G2401 greenhouse gas analyzer and two field-based Gas Chromatography Flame Ionization Detectors (GC-FID) for Non-Methane Hydrocarbons (NMHC) measurements were deployed during two campaigns, one in “urban” (Nicosia) and one in “regional background” (Cape Greko) environment respectively. The campaign at the regional background site consisted in continuous methane and NMHCs (C2-C12) observations using a mobile laboratory that was deployed at the south-eastern edge of the island between December 2021 and February 2022. This location was chosen to capture airmasses of remote south and eastern origin, uninfluenced by local sources. We use these observations to 1) evaluate the significance of long-range transported versus local sources in Cyprus, 2) identify and document regional anthropogenic methane sources, and 3) assess the accuracy of the EDGAR sectoral emission inventory over EMME. Positive Matrix Factorization (PMF) analysis of the NMHC dataset resulted in the identification of four distinct sources namely tropospheric background, urban, heavy oil combustion, and transported from Middle East. The latest occurred during three distinct episodes and on average, had the highest NMHC concentrations. Generally, the different urban and regional signatures/sources displayed good and variable correlations between CH4 and C2 to C6-NMHCs. By investigating the PMF results together with CH4 concentrations and an atmospheric dispersion model (FLEXPART), we provide a comprehensive characterization of the pollution sources at regional scale over the Eastern Mediterranean region.

The emission of mono- and sesquiterpenes from terrestrial vegetation plays a significant role in ecological interactions and atmospheric chemistry. Previous research has suggested that global emissions of these hydrocarbons are largely driven by responses to abiotic stress and can be simulated using a fixed exponential relationship (β coefficient) between different forest ecosystems and environmental conditions. However, our meta-analysis of published emission data (89 studies/835 β coefficients) reveals that the relationship between mono- and sesquiterpene emissions and temperature is more complex than previously thought. We have found that co-occurring environmental stresses can amplify the temperature sensitivity of monoterpene emissions, which is primarily related to the specific plant functional type (PFT). In contrast, the temperature sensitivity of sesquiterpene emissions decreases over the years. On average, warmer ecosystems appear more sensitive, indicating that plants adjust their emission rates in response to thermal stress. When a PFT-dependent β coefficient for monoterpenes was implemented in a biogenic emission model and coupled with a chemistry-climate model, it was found that atmospheric processes are highly sensitive to this coefficient and subject to amplified variations under rising temperatures.

The ASKOS experimental campaign of European Space Agency (ESA) was organised by the National Observatory of Athens, and aimed at the calibration and validation of the Aeolus satellite aerosol/cloud product. Airborne observations were performed by the Climate and Atmosphere Research Centre (CARE-C) team of the Cyprus Institute at the Cesaria Evora International Airport of the island of São Vicente in Cape Verde between 10 and 30 June 2022. These in-situ aerosol measurements were conducted using the advanced Unmanned Aerial Vehicles (UAVs) of the Unmanned System Research Laboratory (USRL), equipped with specialised aerosol in-situ sensors, capturing the Saharan Air Layer (SAL) from ground up to 5.3 km Above Sea Level (ASL). The new custom-designed Composite Bird (CoBi) USRL and Skywalker UAVs (Kezoudi et al., 2021), were equipped with Optical Particle Counters (OPCs), samplers and backscatter sondes.25 UAV vertical flights were performed in total, with 11 of them during night. The altitude of the Marine Boundary Layer (MBL) was mainly observed from ground up to about 1.0 km ASL, whereas during most of the flights, high concentrations of dust particles were found between 1.5 and 5.0 km ASL. Results obtained from OPCs show the presence of particles sizing up to 20 um within MBL and up to 40 um within SAL. Further information on morphology and mineralogy of observed particles will be given by the offline analysis of collected samples under Scanning Electron Microscope (SEM). COBALD observations alongside ground-based lidar measurements agree on the presence of non-spherical particles within dust layers. Ongoing exploitation of airborne observations along with coincident and collocated ground-based measurements will provide a complete picture for comparison with Aeolus data, particularly in relation to aerosols, where we have the most to learn.

With the growing evidence that high particle number concentrations may impact health, modelling their emissions and understanding formation processes is necessary, especially in cities where many people are exposed. As emission inventories of particle numbers and size distribution over cities are usually not available, a methodology is defined to estimate them from PM2.5 emissions and ratios of PM1 / PM2.5 and PM0.1 / PM2.5 by activity sector. In this methodology, a fitting parameter αem is used to redistribute the number concentrations in the lowest emission diameter range. This parameter is chosen by comparing measured and simulated number concentrations during non-nucleation days. The emission size distribution is then finely discretised by conserving both mass and number in each of the size ranges where emissions are specified. The methodology is applied over Greater Paris during the MEGAPOLI campaign (July 2009). Three-dimensional simulations are performed using the chemistry transport model Polair3D/Polyphemus coupled to the aerosol module SSH-aerosol to represent the evolution of particles by condensation, evaporation, coagulation, and nucleation, with a sectional approach for the size distribution. The model is first compared to measurements during non-nucleation days, and the influence over the month of July 2009 of three different nucleation parameterisations is assessed, i.e. binary (sulfuric acid, water), ternary (sulfuric acid, ammonia, water), and heteromolecular (extremely low-volatility organic compounds (ELVOCs) from monoterpenes and sulfuric acid). The modelled number concentrations compare very well to measurements, with an average normalised mean error of 42 % for the daily number concentrations of particles larger than 10 nm and 37 % for the number concentrations of particles larger than 100 nm. The influence of the binary nucleation is low, and the ternary nucleation scheme leads to better simulated number concentrations (in terms of bias and error) at only one site out of three, but it systematically reduces the model to measurement correlation, suggesting that ternary nucleation may not be the dominant process in new particle formation. However, the relative bias and error, as well as the correlation at suburban sites, are systematically improved using the heteromolecular nucleation scheme involving sulfuric acid and ELVOCs from monoterpenes. This suggests that heteromolecular nucleation may be important in cities, especially at suburban sites in summer, and that a better characterisation of the emissions of ELVOC precursors from traffic is needed.

To fight against the first wave of Coronavirus disease 2019 (COVID-19) in 2020, lockdown measures were implemented in most European countries. These lockdowns had well-documented effects on human mobility. We assessed the impact of the lockdown implementation and relaxation on air pollution by comparing daily particulate matter (PM), nitrogen dioxide (NO2), and ozone (O3) concentrations, as well as particle number size distributions (PNSD) and particle light absorption coefficients in-situ measurement data with values expected if no COVID-19 epidemic had occurred at 28 sites across Europe for the period 17 February – 31 May 2020. Expected PM, NO2 and O3 concentrations were calculated from the 2020 Copernicus Atmospheric Monitoring Service (CAMS) Ensemble forecasts, combined with 2019 CAMS Ensemble forecasts and measurement data. On average, lockdown implementations did not lead to a decrease in PM2.5 mass concentrations at urban sites, while relaxations resulted in a +26 ± 21% rebound. The impacts of lockdown implementation and relaxation on NO2 concentrations were more consistent (−29 ± 17 %, and +31 ± 30 %, respectively). The implementation of the lockdown measures also induced statistically significant increases in O3 concentrations at half of all sites (+13 % on average). An enhanced oxidizing capacity of the atmosphere could have boosted the production of secondary aerosol at those places. Changes in the wavelength dependence of the particle light absorption coefficients and PNSD were also examined at 14 and 13 sites, respectively. Since these variables are not calculated by the CAMS model, expected values were estimated from 2017–2019 measurement data. A significant change in the relative contributions of wood and fossil fuel burning to the concentration of black carbon during the lockdown was detected at 7 sites. The contribution of particles smaller than 70 nm to the total number of particles significantly changed at most of the urban sites, with a mean decrease of −7 ± 5 % coinciding with the lockdown implementation. Our study shows that the response of PM2.5 and PM10 mass concentrations to lockdown measures was not systematic at various sites across Europe for multiple reasons, the relationship between road traffic intensity and particulate air pollution being more complex than expected.

Terrestrial vegetation emits vast amounts of monoterpenes into the atmosphere, influencing ecological interactions and atmospheric chemistry. Global emissions, mostly driven by responses to abiotic stress, are simulated as a function of temperature with a fixed exponential relationship (β coefficient) across forest ecosystems and environmental conditions. We applied meta-analysis algorithms on all published monoterpene emission data and show that this relationship is more intricate and sensitive than previously thought. We find that co-occurring environmental stresses amplify the temperature sensitivity of the emissions that is primarily related to the specific plant functional type (PFT). On average, warmer ecosystems appear more sensitive, indicating the adjustment of plants in response to thermal stress. Implementing a PFT-dependent β in a biogenic emission model, coupled with a chemistry – climate model, demonstrated that atmospheric processes are exceptionally dependent on monoterpene emissions which are subject to amplified variations under rising temperatures.

Land–atmosphere interactions govern the process of dust emission and transport. An accurate depiction of these physical processes within numerical weather prediction models allows for better estimating the spatial and temporal distribution of the dust burden and the characterisation of source and recipient areas. In the presented study, the ECMWF-IFS (European Centre for Medium-Range Weather Forecast – Integrated Forecasting System) outputs, produced with and without the assimilation of Aeolus quality-assured Rayleigh–clear and Mie–cloudy horizontal line-of-sight wind profiles, are used as initial or boundary conditions in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate 2-month periods in the spring and autumn of 2020, focusing on a case study in October. The experiments have been performed over the broader eastern Mediterranean and Middle East (EMME) region, which is frequently subjected to dust transport, as it encompasses some of the most active erodible dust sources. Aerosol- and dust-related model outputs (extinction coefficient, optical depth and concentrations) are qualitatively and quantitatively evaluated against ground- and satellite-based observations. Ground-based columnar and vertically resolved aerosol optical properties are acquired through AERONET sun photometers and PollyXT lidar, while near-surface concentrations are taken from EMEP. Satellite-derived vertical dust and columnar aerosol optical properties are acquired through LIVAS (LIdar climatology of Vertical Aerosol Structure) and MIDAS (ModIs Dust AeroSol), respectively. Overall, in cases of either high or low aerosol loadings, the model predictive skill is improved when WRF-Chem simulations are initialised with the meteorological fields of Aeolus wind profiles assimilated by the IFS. The improvement varies in space and time, with the most significant impact observed during the autumn months in the study region. Comparison with observation datasets saw a remarkable improvement in columnar aerosol optical depths, vertically resolved dust mass concentrations and near-surface particulate concentrations in the assimilated run against the control run. Reductions in model biases, either positive or negative, and an increase in the correlation between simulated and observed values was achieved for October 2020.

The climate change impacts on some regions of the planet faster and stronger. These areas are known as the hot spots for climate change and Cyprus (Nicosia) in the Mediterranean is one of these spots. This paper aims to analyze the significant changes of atmospheric aerosol characteristics in 2019 and during the extreme event of 25 April 2019. We study the aerosol optical thickness (AOT), Ångström exponent, single scattering albedo, refractive index (imaginary and real parts), size, and vertical distribution of aerosol particles during the event of a high atmospheric aerosol contamination over Nicosia in details. For this purpose, we used the ground-based lidar, observations of the sun-photometer AERONET Nicosia station, satellite products from the Moderate Resolution Imaging Spectroradiometer (MODIS), and back trajectories of air movements calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). On 23–25 April, according to lidar and sun-photometer observations, strong aerosol pollution over Nicosia was detected. On April 25, 2019, the AOT value exceeds 1.0 at λ = 440 nm. Analysis of the optical and microphysical characteristics supported that the pollution consists of mainly Saharan dust and partly urban aerosols. This assumption was confirmed by HYSPLIT backward trajectories and MODIS images where air masses containing dust particles came from North Africa and from the Eastern part of Europe.

Particulate matter (PM) has become a major concern in terms of human health and climate impact. In particular, the source apportionment (SA) of organic aerosols (OA) present in submicron particles (PM1) has gained relevance as an atmospheric research field due to the diversity and complexity of its primary sources and secondary formation processes. Moreover, relatively simple but robust instruments such as the Aerosol Chemical Speciation Monitor (ACSM) are now widely available for the near-real-time online determination of the composition of the non-refractory PM1. One of the most used tools for SA purposes is the source-receptor positive matrix factorisation (PMF) model. Even though the recently developed rolling PMF technique has already been used for OA SA on ACSM datasets, no study has assessed its added value compared to the more common seasonal PMF method using a practical approach yet. In this paper, both techniques were applied to a synthetic dataset and to nine European ACSM datasets in order to spot the main output discrepancies between methods. The main advantage of the synthetic dataset approach was that the methods' outputs could be compared to the expected "true"values, i.e. the original synthetic dataset values. This approach revealed similar apportionment results amongst methods, although the rolling PMF profile's adaptability feature proved to be advantageous, as it generated output profiles that moved nearer to the truth points. Nevertheless, these results highlighted the impact of the profile anchor on the solution, as the use of a different anchor with respect to the truth led to significantly different results in both methods. In the multi-site study, while differences were generally not significant when considering year-long periods, their importance grew towards shorter time spans, as in intra-month or intra-day cycles. As far as correlation with external measurements is concerned, rolling PMF performed better than seasonal PMF globally for the ambient datasets investigated here, especially in periods between seasons. The results of this multi-site comparison coincide with the synthetic dataset in terms of rolling-seasonal similarity and rolling PMF reporting moderate improvements. Altogether, the results of this study provide solid evidence of the robustness of both methods and of the overall efficiency of the recently proposed rolling PMF approach., Acknowledgements IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). The authors gratefully acknowledge the Romanian National Air Quality Monitoring Network (NAQMN, https://www.calitateaer.ro/public/home-page/?__locale=ro, last access: September 2022) for providing NOx data. Financial support This research has been supported by the Generalitat de Catalunya (grant no. AGAUR 2017 SGR41), the European Cooperation in Science and Technology (grant no. COST Action CA16109 COLOSSAL), the Ministerio de Ciencia, Innovación y Universidades (CAIAC, grant no. PID2019-108990RB-I00 and FEDER, grant no. EQC2018-004598-P.), the Horizon 2020, the Ministry of Education and Research, Romania (grant nos. PN-III-P1-1.1-TE-2019-0340 and 18PFE/30.12.2021, 18N/2019), the Agence Nationale de la Recherche (grant no. PIA, ANR-11_LABX-0005-01), the Conseil Régional Hauts-de-France (CLIMIBIO grant), the Ministère de l'Enseignement Supérieur et de la Recherche (CARA grant), the Environmental Protection Agency (AEROSOURCE, grant no. 2016-CCRP-MS-31), the Department of the Environment, Climate and Communications (AC3 network grant), and the Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (SAMSAM, grant nos. IZCOZ9_177063 and PZPGP2_201992). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

We describe and evaluate a high-resolution real-time air quality forecast system over the Eastern Mediterranean, based on a regional, online coupled atmospheric chemistry and aerosol model. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is used to perform daily, 3 d forecasts of regulated pollutants (NO2, O3, PM2.5) over the Eastern Mediterranean, applying three nested domains with horizontal resolutions of 50, 10 and 2 km, the latter focusing on Cyprus. Natural (dust, sea-salt, biogenic) emissions are calculated online, while anthropogenic emissions are based on the Emissions Database for Global Atmospheric Research – Hemispheric Transport of Air Pollution (EDGAR-HTAP) global emission inventory. A high spatial (1 km) and temporal (hourly) anthropogenic emission inventory is used for the island of Cyprus in the innermost domain. The model skill in forecasting the concentrations of atmospheric pollutants is evaluated using measurements from a network of nine ground stations in Cyprus and compared with the forecasting skill of the EU Copernicus Atmosphere Monitoring Service (CAMS). The forecast of surface temperature, pressure, and wind speed is found to be accurate, with minor discrepancies between the modelled and observed 10 m wind speed at mountainous and coastal sites attributed to the limited representation of the complex topography of Cyprus. Compared to CAMS, the WRF-Chem model predicts with higher accuracy the NO2 mixing ratios at the residential site with a normalized mean bias (NMB) of 7 % during winter and −44 % during summer, whereas the corresponding biases for CAMS are −81 % and −84 %. Due to the high temporal resolution of the anthropogenic emission inventory, the WRF-Chem model captures more accurately the diurnal profiles of NO2 and O3 mixing ratios at the residential site. Background PM2.5 concentrations influenced by long-range transport are overestimated by the WRF-Chem model during winter (NMB = 54 %), whereas the corresponding NMB for CAMS is 11 %. Our results support the adoption of regional, online coupled air quality models over chemical transport models for real-time air quality forecasts.

Unmanned Aerial Vehicles (UAVs) provide a cost-effective way to fill in gaps between surface in-situ observations and remote-sensed data from space. In this study, a novel portable CO2 measuring system suitable for operations on-board small-sized UAVs has been developed and validated. It is based on a low-cost commercial nondispersive near-infrared (NDIR) CO2 sensor (Senseair AB, Sweden), with a total weight of 1058 g, including batteries. The system performs in situ measurements autonomously, allowing for its integration into various platforms. Accuracy and linearity tests in the lab showed that the precision remains within ±1 ppm (1σ) at 1 Hz. Corrections due to temperature and pressure changes were applied following environmental chamber experiments. The accuracy of the system in the field was validated against a reference instrument (Picarro, USA) onboard a piloted aircraft and it was found to be ±2 ppm (1σ) at 1 Hz and ±1 ppm (1σ) at 1 min. Due to its fast response, the system has the capacity to measure CO2 mole fraction changes at 1 Hz, thus allowing the monitoring of CO2 emission plumes and the characteristic of their spatial and temporal distribution. Details of the measurement system and field implementations are described to support future UAV platform applications for atmospheric trace gas measurements.

Over the last few decades, Greater Cairo Megacity has experienced rapid population growth and expansion of its industrial activity. Hosting more than 20 million people, Cairo is considered one of the most polluted megacities in the world. Concentration levels of fine particulate matter (PM2.5) are several times higher than those recommended by the World Health Organization (WHO). Although actions have been designed recently to improve air quality in the framework of a “Pollution Management and Environmental Health program” (PMEH) supported by the World Bank, observational studies assessing the main sources leading to this PM pollution are missing, making difficult to implement and monitor the efficiency of local mitigation strategies.The aim of our study is to investigate atmospheric concentrations levels, temporal variability, as well as major sources, and atmospheric aging of PM in Cairo megacity with a focus on the submicron aerosol fraction (PM1) to better assess human-made activities with lower interference from natural (dust) emissions. A comprehensive suite of on-line and off-line instruments has been set-up to monitor PM1 chemical composition and reactive trace gases (i.e. Volatile Organic Compounds) as a part of the POLCAIR campaign that took place during winter 2019-2020, at an urban background site in Greater Cairo. Chemical composition of PM1 and source apportionment analysis via Positive Matrix Factorization (PMF) on both Q-ACSM (Aerosol Chemical Speciation Monitor, Aerodyne, US) organic mass spectra and co-located filter samples, attributed exceptionally high concentrations of compounds to traffic emissions and diverse combustion sources with pronounced diurnal variability. Two severe pollution episodes were recorded, with hourly mean PM1 concentrations reaching values as high as 300 μg/m3 and lasting for 2 consecutive days favored by low dispersion conditions. Pollutant variability is directly associated with the meteorological conditions, including wind patterns and air mass origins. This helps in recognizing emission hot spots of major anthropogenic PM1 sources. Additionally, the effects of the relative humidity and the role of heterogeneous oxidation reaction mechanisms was investigated. Finally, the multi-variable analyses performed, helped us to better investigate the complex urban atmospheric chemistry in Cairo megacity and to highlight the dynamics of Secondary Organic Aerosol formation.

This study analyzes the optical properties (scattering, absorption coefficients, single scattering albedo) of aerosols in the marine boundary layer of oceanic areas surrounding the East Mediterranean – Middle East (EMME) region. It aims to explore the spatio-temporal variability of aerosols, their atmospheric mixing state, sources and dominant types in a way to assess their role on solar radiation and climate. The current analysis uses measurements obtained in the framework of the AQABA (Air Quality and climate change in the Arabian Basin) cruise, during a two month (1st July - 1st September 2017) period. The cruise consisted of a round trip onboard of a research vessel from south of France to Kuwait, crossing the central-east Mediterranean Sea, Red Sea, Arabian Sea and Persian Gulf.Aerosol scattering and absorption coefficients of both submicron (PM1) and supermicron (PM10) particles were measured, using a polar nephelometer (Aurora 4000 Ecotech Inc) and a dual spot aethalometer (Model AE-33, Magee Scientific), respectively. The meterorological and atmospheric conditions during the whole cruise campaign in July-August 2017 were consisted with local and regional climatology, without intense dust outflows from the arid/desert lands in the Middle East. FLEXPART air mass back-trajectories indicated the potential impact of the continental emissions to examined oceanic regions.Both scattering and absorption coefficients for PM1 and PM10 particles exhibited higher values along the ship cruise in the southern Red Sea, due to continental outflow from east Africa, and in the Persian Gulf due to mixing of natural dust with anthropogenic emissions from the industrial sector and oil refineries. The east Mediterranean exhibited moderate aerosol loading, with intermediate values of scattering Ångström Exponent (SAE) (around 1-1.5), which increased over the Persian Gulf, suggesting enhanced anthropogenic impact against desert dust, while over the Gulf of Aden and the west Arabian Sea, SAE values were very low revealing dust dominance. The absorption Ångström Exponent (AAE) values remained close to 1, indicative of Black Carbon from fossil-fuel combustion, while they increased at regions dominated by dust aerosols, even without high aerosol loading i.e. in the Gulf of Aden and the Arabian Sea.Using the SAE vs. AAE classification scheme, key aerosol types were identified along the ship cruise. The results showed contrasting aerosol characteristics and types for the various sub-regions. The “BC-dominated” type clearly prevailed over the East Mediterranean and Suez Canal, while coarse particles mixed with BC dominated in the Gulf of Aden and the Arabian Sea, where the “dust type” also appeared. In the Persian Gulf, the mixing of anthropogenic pollution with marine aerosols, resulted in a dominant “small/low absorption” aerosol type, characterized by fine aerosols with low spectral dependence of the absorption coefficient.

Unmanned Aerial Vehicle (UAV)-sensor systems allow for cost-effective vertically-resolved in-situ atmospheric observations within the lower troposphere. Taking advantage of the private runway and dedicated airspace of the Unmanned Systems Research Laboratory (USRL; https://usrl.cyi.ac.cy/) of the Cyprus Institute in Orounda (Nicosia, Cyprus), an intensive campaign focusing on mineral dust observations was conducted between 18 October and 18 November 2021. This, involved UAV flights (36 in total) and ground-based active and passive remote-sensing observations during two distinct dust outbreaks over Cyprus.The first dust event occurred between 25 October and 1 November 2021, and HYSPLIT back-trajectories revealed that the observed air masses were mainly originated from NE Sahara (Libya, Egypt). The second dust event was observed from 13 to 18 November 2021. HYSPLIT back-trajectories revealed that the observed air masses at the beginning of the second event were originated from the Middle East (Saudi Arabia, Syria), but the air mass origin switched to NW Saharan dust midways through the event. The Aerosol Optical Depth at 500-nm as measured by our sun-photometers was found to be above 0.2 all the time, and in some days reached up to 0.5. The observed aerosol layers were found to be extending from ground up to 5 km Above Sea Level (ASL).This study presents results of the vertical aerosol structure/height-resolved information of each dust event from its arrival to its departure as observed by instruments on-board the UAVs including: a pair of Universal Cloud and Aerosol Sounding System (UCASS) Optical Particle Counters (OPCs), Printed Optical Particle Spectrometer (POPS) OPC, Compact Optical Backscatter AerosoL Detector (COBALD) and filter samplers.

Due to its geographical location, Cyprus is often affected by dust storms arriving from the largest deserts of the planet, the Sahara, the Arabian Peninsula and the Syrian. In order to characterize dust properties, the Cyprus Atmospheric Observatory (CAO) and the Unmanned Research Laboratory (USRL) of the Cyprus Institute (CYI), in collaboration with the Cyprus Atmospheric Remote sensing Observatory (CARO) of the ERATOSTHENES Centre of Excellence (ECoE) of the Cyprus University of Technology (CUT), performed a research campaign in Fall 2021. Measurements were performed with ground-based aerosol remote sensing systems (lidars, ceilometers and sunphotometers), and UAV based in-situ instruments (OPCs, backscatter sondes, and impactors able to collect dust samples). As part of the remote sensing observations, two depolarized lidars performed measurements from different locations, one from CYI premises in Nicosia and the second one from ECoE-CUT premises in Limassol. The lidar signals provide information about the vertical aerosol profile at the two locations, which can be used to derive the optical properties of dust at different altitudes. Here, we will present first results on the synergy between the continuous vertically extended measurements of lidars and the in-situ measurements from UAV instrumentation during the periods of dust outbreaks. Two dust events occurred from 25 October to 1 November and from 13 to 18 November 2021. During these dust events, the lidars observed depolarized aerosol layers from ground up to 5 km above sea level. The lidar measurements provided the temporal and spatial development of these dust layers, and were also used in real-time for planning the UAV flight schedule. According to backward trajectory analyses, the two dust events had different origins with the first arriving from the Sahara and the second one from the Middle East.

Biomass burning is a significant global source of gaseous and particulate matter emissions to the troposphere. Combustion of biomass releases a complex variety of Volatile Organic Compounds (VOC) that can significantly affect local and regional air quality, human health and atmospheric chemical processes. Here, we present wintertime, high temporal resolution observations made with a Proton Transfer Reaction – Time of Flight - Mass Spectrometer (PTR-ToF-MS) at Ioannina, Greece, during December/January 2022. The city of Ioannina is characterized by intense residential wood burning, that in combination with its topography results in magnified accumulation of gaseous pollutants. We report exceptionally high concentrations for a vast range of VOCs (oxygenated VOCs, aromatics, acids, terpenes etc) that are comparable with the ambient concentrations measured in highly polluted megacities globally. By studying the VOC emission source patterns together with other air quality variables monitored in this study, we characterize the different biomass burning sources and evaluate their significance in atmospheric chemistry and human health.

Located in the Eastern Mediterranean, Cyprus is surrounded by Middle East countries and lies at the crossroads of long-range transported air pollution from Africa, Europe and Asia1. Because concentration levels of air pollution and Particulate Matter (PM), especially, are particularly high in the region, they play a critical role in regional climate and have major adverse health effects 2. However, still very little is known on the main sources of PM affecting Cyprus and their geographical origin, preventing the definition and implementation of efficient local mitigation plans. In the framework of AQ-SERVE and EMME-CARE research projects, 24-h integrated PM filter samples were collected continuously for a period of one year spanning from summer 2016 until summer 2017 at 4 representative locations in Cyprus (urban backgrounds, traffic, and regional background) and analysed with respect to 10 major ions, elemental and organic carbon, main carbohydrates (5 species), 28 major and trace metals and 104 trace organic compounds. To investigate the main PM sources affecting these different locations, source apportionment was performed using US EPA PMF5.0 3 whereas the Lagrangian model FLEXPART along with the Potential Source Contribution Function (PSCF) allowed the identification of their geographical origin. The local and regional contributions to PM mass concentrations were estimated by application of the Lenschow approach 4. Although Sahara and Middle East were identified as the main sources of mineral dust in Cyprus, their chemical composition significantly differ, the latter (Middle East) being loaded not only with crustal elements but also with species from anthropogenic sources such as ammonium sulfate and carbonaceous species which made the PM mass the highest among all PM clusters and highlighting a complex dust-pollution aerosol mixture over this region.Preliminary source apportionment results indicate a predominance of Regionally-processed factor (mainly secondary in nature) contributing alone more than 30% at the urban sites and up to 60% at the regional background station; industrial and power plant emissions from eastern Europe and Turkey being responsible for this high loading in secondary aerosol. Among the identified sources, traffic and biomass burning are mainly emitted locally (within cities) (85 and 70%, respectively). Surprisingly for a region that is strongly impact by desert dust, the share of local and regional sources was almost equal for dust (44 and 56%, respectively).This project has received funding from the European Union’s Horizon 2020 EMME-CARE project (grant agreement No 856612) and the Cyprus Research and Innovation Foundation AQ-SERVE project (RIF INTEGRATED/0916/0016).References1. Lelieveld, J. et al. Global air pollution crossroads over the Mediterranean. Science (80-. ). 298, 794–799 (2002).2. Lelieveld, J. et al. Loss of life expectancy from air pollution compared to other risk factors: A worldwide perspective. Cardiovasc. Res. 116, 1910–1917 (2020).3.Paatero, P. Least squares formulation of robust non-negative factor analysis. Chemom. Intell. Lab. Syst. 37, 23–35 (1997).4. Lenschow, P. et al. Some ideas about the sources of PM10. Atmos. Environ. 35, S23--S33 (2001).

Atmospheric mineral dust influences Earth's radiative budget, cloud formation, and lifetime; has adverse health effects; and affects air quality through the increase of regulatory PM10 concentrations, making its real-time quantification in the atmosphere of strategic importance. Only few near-real-time techniques can discriminate dust aerosol in PM10 samples and they are based on the dust chemical composition. The online determination of mineral dust using aerosol absorption photometers offers an interesting and competitive alternative but remains a difficult task to achieve. This is particularly challenging when dust is mixed with black carbon, which features a much higher mass absorption cross section. We build on previous work using filter photometers and present here for the first time a highly time-resolved online technique for quantification of mineral dust concentration by coupling a high-flow virtual impactor (VI) sampler that concentrates coarse particles with an aerosol absorption photometer (Aethalometer, model AE33). The absorption of concentrated dust particles is obtained by subtracting the absorption of the submicron (PM1) aerosol fraction from the absorption of the virtual impactor sample (VI-PM1 method). This real-time method for detecting desert dust was tested in the field for a period of 2 months (April and May 2016) at a regional background site of Cyprus, in the Eastern Mediterranean. Several intense desert mineral dust events were observed during the field campaign with dust concentration in PM10 up to 45 µg m−3. Mineral dust was present most of the time during the campaign with an average PM10 of about 8 µg m−3. Mineral dust absorption was most prominent at short wavelengths, yielding an average mass absorption cross section (MAC) of 0.24±0.01 m2 g−1 at 370 nm and an absorption Ångström exponent of 1.41±0.29. This MAC value can be used as a site-specific parameter for online determination of mineral dust concentration. The uncertainty of the proposed method is discussed by comparing and validating it with different methods.

As part of the ChArMEx project (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr ), one year of continuous filter sampling was conducted from August 2012 to August 2013 at a rural (coastal) site in Algeria aiming to better document fine aerosol seasonal variability and chemical composition in the Southern part of the Mediterranean. Over 350 filters have been collected, weighted, and analyzed for the main ions and organic and elemental carbon. The obtained mass concentrations varied between 2.5 and 50.6 μg/m3 for PM2.5. The annual modulations of PM2.5 showed higher concentrations in the end summer 2012 and the early summer 2013 (28.50 μg/m3 in August 2012, 20.23 μg/m3 in September 2012, 20.19 μg/m3 in July 2013, and 17.88 μg/m3in August 2013). The particulate organic matter (POM) presented the greatest contribution (50%), followed by the secondary inorganic aerosols (SIA, 27%). The average organic carbon OC concentrations ranged from 1.66 to 6.05 μgC/m3. The average elemental carbon EC concentrations ranged from 0.92 to 3.49 μgC/m3 and contributed 7% of the PM2.5 mass to Bou-Ismail. The average value of the OC /EC ratio was close to 5.1 in Bou-Ismail, and was close to that found in Finokalia 4 (Greece 2004, 2006) but was lower than that of Montseny 11 (Spain 2002–2007) Western Mediterranean Basin (WMB). The concentrations of water-soluble organic carbon WSOC in the PM2.5 ranging from 0.66 to 3.70 μg/m3 recorded the minimum level in March 2013, and the maximum level in August 2012, with an average of 2.02 μg/m3.

International audience; Regulations on ambient particulate matter (PM) are becoming more stringent because of adverse health effects arising from PM exposure. PM-induced oxidant production is a key mechanism behind the observed health effects and is heavily dependent on PM composition. Measurement of the intrinsic oxidative potential (OP) of PM could provide an integrated indicator of PM bioreactivity and could serve as a better metric of PM hazard exposure than PM mass concentration. The OP of two chemically contrasted PM2.5 samples was compared through four acellular assays, and OP predictive capability was evaluated in different cellular assays on two in vitro lung cell models. PM2.5 collected in Paris at a site close to the traffic exhibited a systematically higher OP in all assays compared to PM2.5 enriched in particles from domestic wood burning. Similar results were obtained for oxidative stress, expression of antioxidant enzymes, and pro-inflammatory chemokine in human bronchial epithelial and endothelial cells. The strongest correlations between OP assays and cellular responses were observed with the antioxidant (ascorbic acid and glutathione) depletion (OPAO) assay. Multivariate regression analysis from OP daily measurements suggested that OPAO was strongly correlated with polycyclic aromatic hydrocarbons at the traffic site while it was correlated with potassium for the domestic wood burning sample.

The chemical profiles of PM

The present study investigated comprehensively the atmospheric occurrence and fate of an extensive range of polychlorinated biphenyls (PCBs; forty-two congeners), organochlorine pesticides (OCPs; twenty-seven emerging and legacy agrochemicals) and polycyclic aromatic hydrocarbons (PAHs; fifty parent and alkylated members, including the non USEPA-16 listed toxic ones), in both gas and particulate phase of the scarcely monitored atmosphere over Cyprus for the first time. Parent-metabolite concentration ratios suggested fresh application for dichlorodiphenyl-trichloroethanes (DDTs), dicofol, hexachlorocyclohexanes, endosulfan and chlorothalonil, particularly during spring (April-May). Regressions of logarithms of partial pressure against ambient temperature revealed that secondary recycling from contaminated terrestrial surfaces regulates the atmospheric level variability of PCBs, DDTs, aldrin, chlordane, dicofol, heptachlor and endosulfan. Enthalpies of surface-air exchange (∆H