Suchergebnisse

This study has been supported by the Research Council of Norway (project ID: 275407, COMBAT - Quantification of Global Ammonia Sources constrained by a Bayesian Inversion Technique). Nikolaos Evangeliou and Sabine Eckhardt received funding from the Arctic Monitoring & Assessment Programme (AMAP). John Backman was supported by the Academy of Finland project Novel Assessment of Black Carbon in the Eurasian Arctic: From Historical Concentrations and Sources to Future Climate Impacts (NABCEA; project no. 296302), the Academy of Finland Centre of Excellence programme (project no. 307331) and COST Action CA16109 Chemical On-Line cOmpoSition and Source Apportionment of fine aerosoL, COLOSSAL. The research leading to the ACTRIS measurements has received funding from the European Union's Horizon 2020 Research And Innovation programme (grant agreement no. 654109) and the Cloudnet project (European Union contract EVK2-2000-00611). ; All measurement data and model outputs used for the present publication are publicly available and can be downloaded from https://doi.org/10.21336/gen.b5vj-sn33 (Evangeliou et al., 2020) or upon request to the corresponding author. All prior emission datasets are also available for download. ECLIPSE emissions can be obtained from http://www.iiasa.ac.at/web/home/research/researchPrograms/air/Global_emissions.html (Klimont et al., 2017), EDGAR version HTAP_V2.2 from http://edgar.jrc.ec.europa.eu/methodology.php# (Janssens-Maenhout et al., 2015), ACCMIP version 5 from http://accent.aero.jussieu.fr/ACCMIP_metadata.php (Lamarque et al., 2010) and PKU from http://inventory.pku.edu.cn (Peking University, 2021). FLEXPART is publicly available and can be downloaded from https://www.flexpart.eu (Pisso et al., 2019) and FLEXINVERT+ from https://flexinvert.nilu.no (Thompson and Stohl, 2014). MERRA-2 reanalysis data can be obtained from https://disc.gsfc.nasa.gov (NASA Earth Data, 2021) and AERONET measurements from https://aeronet.gsfc.nasa.gov (Holben et al., 1998). ; The supplement related to this article is available online at: https://doi.org/10.5194/acp-21-2675-2021-supplement. ; Following the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for COVID-19 in December 2019 in Wuhan (China) and its spread to the rest of the world, the World Health Organization declared a global pandemic in March 2020. Without effective treatment in the initial pandemic phase, social distancing and mandatory quarantines were introduced as the only available preventative measure. In contrast to the detrimental societal impacts, air quality improved in all countries in which strict lockdowns were applied, due to lower pollutant emissions. Here we investigate the effects of the COVID-19 lockdowns in Europe on ambient black carbon (BC), which affects climate and damages health, using in situ observations from 17 European stations in a Bayesian inversion framework. BC emissions declined by 23 kt in Europe (20 % in Italy, 40 % in Germany, 34 % in Spain, 22 % in France) during lockdowns compared to the same period in the previous 5 years, which is partially attributed to COVID-19 measures. BC temporal variation in the countries enduring the most drastic restrictions showed the most distinct lockdown impacts. Increased particle light absorption in the beginning of the lockdown, confirmed by assimilated satellite and remote sensing data, suggests residential combustion was the dominant BC source. Accordingly, in central and Eastern Europe, which experienced lower than average temperatures, BC was elevated compared to the previous 5 years. Nevertheless, an average decrease of 11 % was seen for the whole of Europe compared to the start of the lockdown period, with the highest peaks in France (42 %), Germany (21 %), UK (13 %), Spain (11 %) and Italy (8 %). Such a decrease was not seen in the previous years, which also confirms the impact of COVID-19 on the European emissions of BC. ; Research Council of Norway ; rctic Monitoring & Assessment Programme (AMAP). ; Academy of Finland project Novel Assessment of Black Carbon in the Eurasian Arctic: From Historical Concentrations and Sources to Future Climate Impacts (NABCEA) 296302 ; Academy of Finland 307331 ; European Cooperation in Science and Technology (COST) CA16109 ; European Union's Horizon 2020 Research And Innovation programme 654109 ; Cloudnet project European Union EVK2-2000-00611

Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system. ; European Commission Joint Research Centre 654109 ; European ERDF funds through different Spanish R&D projects of the Spanish Ministerio de Economia, Industria y Competitividad ; NorthWest University ; University of Helsinki ; Academy of Finland 272041 ; Academy of Finland project Greenhouse gas 269095 296302 ; Korea Meteorological Administration Research and Development Program "Development of Monitoring and Analysis Techniques for Atmospheric Composition in Korea KMA2018-00522 ; National Research Foundation of Korea 2017R1D1A1B06032548 ; Korea Meteorological Administration Research and Development Program KMI2018-01111 ; Taiwan Environmental Protection Administration ; Ministry of Research, France ; French Ministry of the Environment ; United States Environmental Protection Agency ; MeteoSwiss (GAW-CH aerosol monitoring programme) ; Swiss State Secretariat for Education, Research and Innovation (SERI) ; Ministry of Education, Youth and Sports of CR within National Sustainability Program I (NPU I) LO1415 ; ERDF "ACTRISCZ RI" CZ.02.1.01/0.0/0.0/16_013/0001315 CGL2017-85344-R MINECO/AEI/FEDER ; TIGAS-CM (Madrid Regional Government) Y2018/EMT-5177 ; AIRTECCM (Madrid Regional Government) P2018/EMT4329 REDMAAS2020 RED2018-102594-T CIENCIA ; Spanish Ministry of Economy, Industry and Competitiveness ; European Union (EU) CGL2016-78594-R ; Generalitat de Catalunya AGAUR 2017 SGR41 ; National Institute for Aerospace Technology ; Ministerio Espanol de Economia, Industria y Competitividad (MINECO) MIS 5021516 ; Competitiveness, Entrepreneurship and Innovation ; NSRF ; Ministry of Education, Universities and Research (MIUR) ; Norwegian Environment Agency ; Swedish FORMAS; Swedish Research Council (VR) ; Magnus Bergvall foundation ; Marta och Erik Holmberg foundation ; Swedish EPA

A reference dataset of multi-wavelength particle light scattering and hemispheric backscattering coefficients for different relative humidities (RH) between RH = 30 and 95% and wavelengths between λ = 450 nm and 700 nm is described in this work. Tandem-humidified nephelometer measurements from 26 ground-based sites around the globe, covering multiple aerosol types, have been re-analysed and harmonized into a single dataset. The dataset includes multi-annual measurements from longterm monitoring sites as well as short-term field campaign data. The result is a unique collection of RH-dependent aerosol light scattering properties, presented as a function of size cut. This dataset is important for climate and atmospheric model-measurement inter-comparisons, as a means to improve model performance, and may be useful for satellite and remote sensing evaluation using surface-based, in-situ measurements. ; This work was essentially supported by the Department of Energy (USA) under the project DE-SC0016541. The humidified nephelometer measurements at BRW and SGP were funded by the U.S. Department of Energy Atmospheric Radiation Measurement (DOE/ARM) program via Argonne National Laboratory. The DOE/ARM Program Climate Research Facility and the DOE Atmospheric Sciences Program funded the AMF deployments (FKB, GRW, HFE, MAO, NIM, PGH, PVC, PYE). Measurements at KCO were supported by the National Science Foundation (Grant ATM-961288). The CBG humidified nephelometer measurements were supported by the NOAA Climate Goal program. The HLM measurements were supported by DOE's ASP program under grant DE-A102-05ER63996. The GSN measurements were supported by NSF grant 0138250. The humidified nephelometer measurements operated by the Paul Scherrer Institute (CES, JFJ, MEL, MHD, ZEP, and HYY) and the instrument development itself were financially supported by the projects ESA Climate Change Initiative Aerosol cci (ESRIN/Contract No. 4000101545/10/I-AM), the Swiss National Science Foundation (Advanced Postdoc.Mobility fellowship; Grant No. P300P2_147776), and by the EC-projects Global Earth Observation and Monitoring (GEOmon, contract 036677) and European Supersites for Atmospheric Atmospheric Aerosol Research (EUSAAR, contract 026140). The measurements of the University of Granada (UGR) were supported by the Spanish Agencia Estatal de Investigación, AEI, through projects CGL2016-81092-R and CGL2017-90884- REDT and the European Union's Horizon 2020 research and innovation program through project ACTRIS-2 (Grant Agreement No. 654109). The Lin'an site observation was supported by the National Natural Science Foundation of China (41475118). We thank Markus Fiebig, Richard Olav Rud, and Paul Eckhardt (NILU, Norway) for their great help to prepare and submit the data files to the EBAS and ACTRIS data centre. Open access funding provided by Stockholm University.

We interpret here the variability of levels of carbonaceous aerosols based on a 12 yr database from 78 monitoring stations across Spain specially compiled for this article. Data did not evidence any spatial trends of carbonaceous aerosols across the country. Conversely, results show marked differences in average concentrations from the cleanest, most remote sites (around 1 μg m−3 of non-mineral carbon (nmC), mostly made of organic carbon (OC) with very little elemental carbon (EC), around 0.1 μg m−3; OC / EC = 12–15), to the highly polluted major cities (8–10 μg m−3 of nmC; 3–4 μg m−3 of EC; 4–5 μg m−3 of OC; OC / EC = 1–2). Thus, urban (and very specific industrial) pollution was found to markedly increase levels of carbonaceous aerosols in Spain, with much lower impact of biomass burning and of biogenic emissions. Correlations between yearly averaged OC / EC and EC concentrations adjust very well to a potential equation (OC = 3.37 EC0.326, R2 = 0.8). A similar equation is obtained when including average concentrations obtained at other European sites (OC = 3.60EC0.491, R2 = 0.7). A clear seasonal variability in OC and EC concentrations was detected. Both OC and EC concentrations were higher during winter at the traffic and urban sites, but OC increased during the warmer months at the rural sites. Hourly equivalent black carbon (EBC) concentrations at urban sites accurately depict road traffic contributions, varying with distance from road, traffic volume and density, mixing-layer height and wind speed. Weekday urban rush-hour EBC peaks are mimicked by concentrations of primary gaseous emissions from road traffic, whereas a single midday peak is characteristic of remote and rural sites. Decreasing annual trends for carbonaceous aerosols were observed between 1999 and 2011 at a large number of stations, probably reflecting the impact of the EURO4 and EURO5 standards in reducing the diesel PM emissions. This has resulted in some cases in an increasing trend for NO2 / (OC + EC) ratios as these standards have been much less effective for the abatement of NOx exhaust emissions in passenger diesel cars. This study concludes that EC, EBC, and especially nmC and OC + EC are very good candidates for new air quality standards since they cover both emission impact and health-related issues. ; This study was supported by the Ministry of Agriculture, Food and the Environment of Spain, the Ministry of Economy and Competitivity (MINECO) of Spain and FEDER funds under the projects VAMOS (CGL2010-19464/CLI), PRISMA (CGL2012-39623-C02-01), GRACCIE (CSD 2007-00067), POLLINDUST (CGL2011-26259) and UHU (CGL2011- 28025); and by AGAUR-Generalitat de Catalunya (2009 SGR 00008) and LIFE + AIRUSE (LIFE11-ENV/ES/000584). The Montseny site forms part of the ACTRIS network (European Union Seventh Framework Programme (FP7/2007-2013) project no. 262254), formerly EUSAAR (EUSAAR R113-CT-2006-026140). Funding was also received for the Andalucía sites from projects 2007-RNM027329 and 2011-RNM7800 (Department of Innovation Science and Enterprise, Andalusia Autonomous Government) M. C. Minguillón was funded by the JAE-Doc CSIC programme, co-funded by the European Social Fund (ESF).

We present an automatic aerosol classification method based solely on the European Aerosol Research Lidar Network (EARLINET) intensive optical parameters with the aim of building a network-wide classification tool that could provide near-real-time aerosol typing information. The presented method depends on a supervised learning technique and makes use of the Mahalanobis distance function that relates each unclassified measurement to a predefined aerosol type. As a first step (training phase), a reference dataset is set up consisting of already classified EARLINET data. Using this dataset, we defined 8 aerosol classes: clean continental, polluted continental, dust, mixed dust, polluted dust, mixed marine, smoke, and volcanic ash. The effect of the number of aerosol classes has been explored, as well as the optimal set of intensive parameters to separate different aerosol types. Furthermore, the algorithm is trained with literature particle linear depolarization ratio values. As a second step (testing phase), we apply the method to an already classified EARLINET dataset and analyze the results of the comparison to this classified dataset. The predictive accuracy of the automatic classification varies between 59% (minimum) and 90% (maximum) from 8 to 4 aerosol classes, respectively, when evaluated against pre-classified EARLINET lidar. This indicates the potential use of the automatic classification to all network lidar data. Furthermore, the training of the algorithm with particle linear depolarization values found in the literature further improves the accuracy with values for all the aerosol classes around 80 %. Additionally, the algorithm has proven to be highly versatile as it adapts to changes in the size of the training dataset and the number of aerosol classes and classifying parameters. Finally, the low computational time and demand for resources make the algorithm extremely suitable for the implementation within the single calculus chain (SCC), the EARLINET centralized processing suite. ; The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 602014 (project ECARS – East European Centre for Atmospheric Remote Sensing) and from the European Union's Horizon 2020 research program for societal challenges – smart, green and integrated transport under grant agreement no. 723986 (project EUNADICS-AV – European Natural Disaster Coordination and Information System for Aviation).

This is a preprint version of a paper accepted to be published in "Foyo-Moreno, I.; Alados-Arboledas, I.; Alados-Arboledas, L. A new empirical model to estimate hourly diffuse photosynthetic photon flux density. Atmospheric Research, 203: 189-196 (2018)", doi: https://doi.org/10.1016/j.atmosres.2017.12.012 ; Knowledge of the photosynthetic photon flux density (Qp) is critical in different applications dealing with climate change, plant physiology, biomass production, and natural illumination in greenhouses. This is particularly true regarding its diffuse component (Qpd), which can enhance canopy light-use efficiency and thereby boost carbon uptake. Therefore, diffuse photosynthetic photon flux density is a key driving factor of ecosystem-productivity models. In this work, we propose a model to estimate this component, using a previous model to calculate Qp and furthermore divide it into its components. We have used measurements in urban Granada (southern Spain), of global solar radiation (Rs) to study relationships between the ratio Qpd/Rs with different parameters accounting for solar position, water-vapour absorption and sky conditions. The model performance has been validated with experimental measurements from sites having varied climatic conditions. The model provides acceptable results, with the mean bias error and root mean square error varying between − 0.3 and − 8.8% and between 9.6 and 20.4%, respectively. ; This work was supported by the Andalusia Regional Government project P12-RNM-2409, by the Spanish Ministry of Economy and Competitiveness projects CGL2013-45410-R and CGL2016-81092-R, and by the European Union's Horizon 2020 research and innovation programme project ACTRIS-2 (grant agreement No 654109).

"This is the pre-peer reviewed version of the following article: Foyo-Moreno, I., Alados, I. and Alados-Arboledas, L. (2017), A new conventional regression model to estimate hourly photosynthetic photon flux density under all sky conditions. Int. J. Climatol. doi:10.1002/joc.5063, which has been published in final form at hppt://dx.doi.org/10.1002/joc.5063 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving." ; In this work we propose a new and simple empirical model to estimate photosynthetic photon flux density under all sky conditions, developed using experimental measurements carried out at Granada, an urban site in Southeastern Spain during two recent years (2014-2015). The model uses the solar zenith angle and clearness index as input parameters, and thus needs only global irradiance measurements usually registered in most radiometric networks. Five stations located in the northern and southern hemisphere with different climatological characteristics at Europe, Asia and America (Spain, Japan and Argentina) were used to validate the model. The model provides satisfactory results, giving low mean bias error for all stations, particularly Mean Bias Error, MBE, being less than 1% in absolute values in three stations and Root Mean Square Error, RMSE, below 6% for all stations except one with 6.1%. These results show better accuracy in comparison to other earlier empirical models and suggest the effectiveness of the model by its general applicability. ; Andalusia Regional Government. Grant Numbers: P11-RNM-7186, P12-RNM-2409 ; Spanish Ministry of Economy and Competitiveness. Grant Numbers: CGL2016-81092-R, CGL2013-45410-R, CGL2014-52838-C2-1-R ; European Union's Horizon 2020 Research And Innovation Programme. Grant Number: 654109

The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-climate interactions. A special observing period (SOP-1a) including intensive airborne measurements was performed in the framework of the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) project during the Mediterranean dry season over the western and central Mediterranean basins, with a focus on aerosol-radiation measurements and their modeling. The SOP-1a took place from 11 June to 5 July 2013. Airborne measurements were made by both the ATR-42 and F-20 French research aircraft operated from Sardinia (Italy) and instrumented for in situ and remote-sensing measurements, respectively, and by sounding and drifting balloons, launched in Minorca. The experimental setup also involved several ground-based measurement sites on islands including two ground-based reference stations in Corsica and Lampedusa and secondary monitoring sites in Minorca and Sicily. Additional measurements including lidar profiling were also performed on alert during aircraft operations at EARLINET/ACTRIS stations at Granada and Barcelona in Spain, and in southern Italy. Remote-sensing aerosol products from satellites (MSG/SEVIRI, MODIS) and from the AERONET/PHOTONS network were also used. Dedicated meso-scale and regional modeling experiments were performed in relation to this observational effort. We provide here an overview of the different surface and aircraft observations deployed during the ChArMEx/ADRIMED period and of associated modeling studies together with an analysis of the synoptic conditions that determined the aerosol emission and transport. Meteorological conditions observed during this campaign (moderate temperatures and southern flows) were not favorable to producing high levels of atmospheric pollutants or intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign, with the main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 and 0.6 (at 440 nm) over the western and central Mediterranean basins. One important point of this experiment concerns the direct observations of aerosol extinction onboard the ATR-42, using the CAPS system, showing local maxima reaching up to 150Mm(-1) within the dust plume. Non-negligible aerosol extinction (about 50Mm(-1)) has also been observed within the marine boundary layer (MBL). By combining the ATR- 42 extinction coefficient observations with absorption and scattering measurements, we performed a complete optical closure revealing excellent agreement with estimated optical properties. This additional information on extinction properties has allowed calculation of the dust single scattering albedo (SSA) with a high level of confidence over the western Mediterranean. Our results show a moderate variability from 0.90 to 1.00 (at 530 nm) for all flights studied compared to that reported in the literature on this optical parameter. Our results underline also a relatively low difference in SSA with values derived near dust sources. In parallel, active remote-sensing observations from the surface and onboard the F-20 aircraft suggest a complex vertical structure of particles and distinct aerosol layers with sea spray and pollution located within the MBL, and mineral dust and/or aged North American smoke particles located above (up to 6–7 km in altitude). Aircraft and balloon-borne observations allow one to investigate the vertical structure of the aerosol size distribution showing particles characterized by a large size (> 10 μm in diameter) within dust plumes. In most of cases, a coarse mode characterized by an effective diameter ranging between 5 and 10 μm, has been detected above the MBL. In terms of shortwave (SW) direct forcing, in situ surface and aircraft observations have been merged and used as inputs in 1-D radiative transfer codes for calculating the aerosol direct radiative forcing (DRF). Results show significant surface SW instantaneous forcing (up to (-90)Wm(-2) at noon). Aircraft observations provide also original estimates of the vertical structure of SW and LW radiative heating revealing significant instantaneous values of about 5 K per day in the solar spectrum (for a solar angle of 30 ) within the dust layer. Associated 3-D modeling studies from regional climate (RCM) and chemistry transport (CTM) models indicate a relatively good agreement for simulated AOD compared with observations from the AERONET/PHOTONS network and satellite data, especially for long-range dust transport. Calculations of the 3-D SW (clear-sky) surface DRF indicate an average of about -10 to -20Wm(-2) (for the whole period) over the Mediterranean Sea together with maxima (-50Wm(-2)) over northern Africa. The top of the atmosphere (TOA) DRF is shown to be highly variable within the domain, due to moderate absorbing properties of dust and changes in the surface albedo. Indeed, 3-D simulations indicate negative forcing over the Mediterranean Sea and Europe and positive forcing over northern Africa. Finally, a multiyear simulation, performed for the 2003 to 2009 period and including an ocean–atmosphere (O–A) coupling, underlines the impact of the aerosol direct radiative forcing on the sea surface temperature, O–A fluxes and the hydrological cycle over the Mediterranean. ; French National Research Agency (ANR) ANR-11-BS56-0006 ; ADEME ; French Atomic Energy Commission ; CNRS-INSU and Meteo-France through the multidisciplinary programme MISTRALS (Mediterranean Integrated Studies aT Regional And Local Scales) ; CORSiCA project - Collectivite Territoriale de Corse through Fonds Europeen de Developpement Regional of the European Operational Program ; Contrat de Plan Etat-Region ; European Union's Horizon 2020 research and innovation program 654169 ; Spanish Ministry of Economy and Competitivity TEC2012-34575 ; Science and Innovation UNPC10-4E-442 ; European Union (EU) ; Department of Economy and Knowledge of the Catalan Autonomous Government SGR 583 ; Andalusian Regional Government P12-RNM-2409 ; Spanish Government CGL2013-45410-R 262254

The eruption of the Icelandic volcano Eyjafjallajökull in April–May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4-D) distribution of the Eyjafjallajökull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April–26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at http://www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at http://www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local planetary boundary layer (PBL). After 19 April 2010, volcanic particles were detected over southern and south-eastern Europe. During the first half of May (5–15 May), material emitted by the Eyjafjallajökull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. The last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4-D distribution of volcanic aerosol layering and optical properties on European scale reported here provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events. ; The financial support for EARLINET by the European Union under grant RICA 025991 in the Sixth Framework Programme is gratefully acknowledged. Since 2011 EARLINET has been integrated in the ACTRIS Research Infrastructure Project supported by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 262254. The authors acknowledge the ESA financial support under the ESRIN contract 21769/08/I-OL and 22202/09/I-EC. Additional financial support has been received from the Andalusia Regional Government through project P10-RNM-6299 and from the Spanish Ministry of Science and Technology through projects CGL2010-18782, and CSD2007-00067.

Measurements of aerosol optical properties and aerosol number size distribution obtained during the period from December 2005 to November 2007 at Granada, an urban site in south-eastern Spain, are analyzed. Large variations of the measured variables have been found, and related to variations in emissions sources and meteorological conditions. High values of aerosol absorption and scattering coefficients are obtained during winter and low values are measured during summer. This seasonal pattern in the surface aerosol optical properties is opposite to the seasonal cycle showed by columnar aerosol optical depth. The differences in the seasonal features of the surface and column-integrated data are related to seasonal variations in the aerosol vertical distribution, aerosol sources and boundary layer height. In winter the number density of "fine" particles (0.5

In this work we adapt an empirical model to estimate ultraviolet erythemal irradiance (UVER) using experimental measurements carried out at seven stations in Spain during four years (2000–2003). The measurements were taken in the framework of the Spanish UVB radiometric network operated and maintained by the Spanish Meteorological Institute. The UVER observations are recorded as half hour average values. The model is valid for all-sky conditions, estimating UVER from the ozone columnar content and parameters usually registered in radiometric networks, such as global broadband hemispherical transmittance and optical air mass. One data set was used to develop the model and another independent set was used to validate it. The model provides satisfactory results, with low mean bias error (MBE) for all stations. In fact, MBEs are less than 4% and root mean square errors (RMSE) are below 18% (except for one location). The model has also been evaluated to estimate the UV index. The percentage of cases with differences of 0 UVI units is in the range of 61.1% to 72.0%, while the percentage of cases with differences of ±1 UVI unit covers the range of 95.6% to 99.2%. This result confirms the applicability of the model to estimate UVER irradiance and the UV index at those locations in the Iberian Peninsula where there are no UV radiation measurements. ; This work was supported by CICYT from the Spanish Ministry of Science and Technology through projects CIRRUS REN2003-03175 and PANDORA-CALIPSO CGL2004- 05984-C07-03, REN 2003- 03175 and Andalusian Regional Government project P06-RNM-01503. The "Instituto Nacional de Meteorología" kindly provided the radiometric and meteorological information for the stations used in this study.

Urban boundary layer characterization is currently a challenging and relevant issue, because of its role in weather and air quality modelling and forecast. In many cities, the effect of complex topography at local scale makes this modelling even more complicated. This is the case of mid-latitude urban areas located in typical basin topographies, which usually present low winds and high turbulence within the atmospheric boundary layer (ABL). This study focuses on the analysis of the first ever measurements of wind with high temporal and vertical resolution throughout the ABL over a medium-sized city surrounded by mountains in southern Spain. These measurements have been gathered with a scanning Doppler lidar system and analyzed using the Halo lidar toolbox processing chain developed at the Finnish Meteorological Institute. We have used the horizontal wind product and the ABL turbulence classification product to carry out a statistical study using a two-year database. The data availability in terms of maximum analyzed altitudes for statistically significant results was limited to around 1000–1500mabove ground level (a.g.l.) due to the decreasing signal intensity with height that also depends on aerosol load. We have analyzed the differences and similarities in the diurnal evolution of the horizontal wind profiles for different seasons and their modelling with Weibull and von Mises probability distributions, finding a general trend of mean daytime wind from the NW with mean speeds around 3–4 m/s at low altitudes and 6–10 m/s at higher altitudes, and weaker mean nocturnal wind from the SE with similar height dependence. The highest speeds were observed during spring, and the lowest during winter. Finally, we studied the turbulent sources at the ABL with temporal (for each hour of the day) and height resolution. The results show a clear convective activity during daytime at altitudes increasing with time, and a significant wind-shear-driven turbulence during night-time. ; Spanish Government FPU14/03684 ; Ministerio ...

This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intra-annual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 654109, ACTRIS (project no. 262254), ACTRIS-PPP (project no. 739530). We thank the International Foundation High Altitude Research Stations JFJ (Jungfraujoch) and Gornergrat (HFSJG), which made it possible to carry out the experiments at the High Altitude Research JFJ Station and the support of MeteoSwiss within the Swiss programme of the Global Atmosphere Watch (GAW) of the WMO. The MAD (Madrid) station is co-financed by the PROACLIM (CGL2014-52877-R) project. The SMR (Hyytiälä) station acknowledges BACCHUS (project no. 603445), CRAICC (project no. 26060) and the Academy of Finland (project no. 3073314). The UGR (Granada) station is co-financed by the Spanish Ministry of Economy and Competitiveness through project CGL2016-81092-R. Measurements at MSY (Montseny) and MSA (Montsec) stations were supported by the MINECO (Spanish Ministry of Economy, Industry and Competitiveness) and FEDER funds under the PRISMA project (CGL2012-39623-C02/00) and under the HOUSE project (CGL2016-78594-R), by the MAGRAMA (Spanish Ministry of Agriculture, Food and Environment) and by the Generalitat de Catalunya (AGAUR 2014 SGR33, AGAUR 2017 SGR41 and the DGQA). Measurements at IZO (Izaña) were supported by the AEROATLAN project (CGL2015-17 66229-P), co-funded by the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund. Station KOS (Košetice) is supported by the Ministry of Education, Youth and Sports of the Czech Republic within the project to support the national research infrastructure ACTRIS – participation of the Czech Republic (ACTRIS-CZ – LM2015037). Measurements at PUY (Puy de Dôme) were partly supported by CNRS-INSU, University Clermont-Auvergne, OPGC and the french CLAP programme. The PAL (Pallas) station acknowledges KONE Foundation, Academy of Finland (project no. 269095 and no. 296302). CHC (Mt Chacaltaya) station received support from Institut de Recherche pour le Développement (IRD) under both Jeune Equipe programme attributed to LFA and support to ACTRIS-FR programme. CHC received grants from Labex OSUG@2020 (Investissements d'avenir – ANR10 LABX56). Marco Pandolfi is funded by a Ramón y Cajal Fellowship (RYC-2013-14036) awarded by the Spanish Ministry of Economy and Competitiveness. The authors would like to express their gratitude to David Carslaw and Karl Ropkins for providing the OpenAir software used in this paper (Carslaw and Ropkins, 2012; Carslaw, 2012). We also thank the co-editor Andreas Petzold and two anonymous reviewers for their constructive comments.

This paper provides an account of observed variations in Black carbon (BC) aerosol concentrations and their induced radiative forcing for the first time over Granada a measurement site in Southeastern Iberian Peninsula. Column-integrated BC concentrations were retrieved for the period 2005–2012. Monthly averages of BC concentrations (± one standard deviation) ranged from higher values in January and December with 4.0 ± 2.5 and 4 ± 3 mg/m², respectively, to lower values in July and August with 1.6 ± 1.2 and 2.0 ± 0.5 mg/m², respectively. This reduction is not only observed in the average values, but also in the median, third and first quartiles. The average BC concentration in winter (3.8 ± 0.6 mg/m²) was substantially higher than in summer (1.9 ± 0.3 mg/m²), being the eight-year average of 2.9 ± 0.9 mg/m². The reduction in the use of fossil fuels during the economic crisis contributed significantly to reduced atmospheric loadings of BC. According to our analysis this situation persisted until 2010. BC concentration values were analyzed in terms of air mass influence using cluster analysis. BC concentrations for cluster 1 (local and regional areas) showed high correlations with air masses frequency in winter and autumn. In these seasons BC sources were related to the intense road traffic and increased BC emissions from domestic heating. High BC concentrations were found in autumn just when air mass frequencies for cluster 3 (Mediterranean region) were more elevated, suggesting that air masses coming from that area transport biomass burning particles towards Granada. BC aerosol optical properties were retrieved from BC fraction using aerosol AERONET size volume distribution and Mie theory. A radiative transfer model (SBDART) was used to estimate the aerosol radiative forcing separately for composite aerosol (total aerosols) and exclusively for BC aerosols. The mean radiative forcing for composite aerosol was + 23 ± 6 W/m² (heating rate of + 0.21 ± 0.06 K/day) and + 15 ± 6 W/m² for BC aerosol (heating rate of + 0.15 ± 0.06 K/day). These values of radiative forcing and heating rate for BC aerosol represent about 70% of their values for composite aerosol, which highlights the crucial role that BC aerosols play in modifying the radiation budget and climate. ; This work was supported by the Andalusia Regional Government through project P12-RNM-2409, by the Spanish Ministry of Economy and Competitiveness through projects CGL2013-45410-R and CGL2016-81092-R and by the European Union's Horizon 2020 research and innovation programme through project ACTRIS-2 (grant agreement No. 654109). The authors thankfully acknowledge the FEDER program for the instrumentation used in this work. Antonio Valenzuela thanks Universidad de Granada for the award of a postdoctoral grant ("Plan Propio. Programa 8. Convocatoria 2014"). The work is co-funded by the European Union through the European Regional Development Fund, included in the COMPETE 2020 (Operational Program Competitiveness and Internationalization) through the ICT project (UID/GEO/04683/2013) with the reference POCI-01-0145-FEDER-007690. CIMEL Calibration was performed at the AERONET-EUROPE calibration center, supported by ACTRIS (European Union Seventh Framework Program (FP7/2007-2013) under grant agreement no. 262254. The authors express gratitude to the NOAA Air Resources Laboratory (ARL) for the HYSPLIT transport and dispersion model (http://ready.arl.noaa.gov/HYSPLIT.php). The author acknowledges the funding provided by the Institute of Earth Sciences (ICT), under contracts UID/GEO/04683/2013 with FCT (the Portuguese Science and Technology Foundation), and COMPETEPOCI-01-0145-FEDER-007690.

Sky imagers have been used for cloud detection and classification in the last years, and one of the applications of these instruments is the use of cloud information in forecast algorithms for solar power technologies. These algorithms depend on an accurate classification of the complete sky dome cloud cover, but most system fail in the proximity of the sun due to saturation in the images. This work proposes a new method for cloud detection with sky imagers using images taken with different exposure times and applying an adaptive threshold to each one. The use of multiple exposure times avoids the saturation of the image in the vicinity of the sun position, while the adaptive threshold applied to the images helps in the accurate detection of cloud coverage, especially in the circumsolar area. The method is tested with a commercial sky imager, paying special attention to the detection of clouds close to the sun position. A case study is analyzed, showing an accurate detection of clouds in the vicinity of the sun. The method is also validated using statistical values for data recorded during almost one month which cover a great variety of cloudiness cases. For this purpose, the detection of clouds in the sun position is compared against the reduction of the direct normal irradiance (DNI) with respect to a modeled DNI. ; This work was supported by the Andalusia Regional Government through projectsP10-RNM-6299 and P12-RNM-2409, ; Spanish Ministry of Economy and Competitiveness through projectsCGL2013-45410-R. ; EU through ACTRIS project (EU INFRA-2010-1.1.16-262254).