A new empirical model to estimate hourly diffuse photosynthetic photon flux density

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.2017.12.012Knowledge 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)

Adaptation of an empirical model for erythemal ultraviolet irradiance

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

Changes in black carbon emissions over Europe due to COVID-19 lockdowns

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 Norwayrctic 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) 296302Academy of Finland 307331European Cooperation in Science and Technology (COST) CA16109European Union's Horizon 2020 Research And Innovation programme 654109Cloudnet project European Union EVK2-2000-0061

The variability of mass concentrations and source apportionment analysis of equivalent black carbon across urban Europe

This study is supported by the RI-URBANS project (Research Infrastructures Services Reinforcing Air Quality Monitoring Capacities in European Urban & amp; Industrial Areas, European Union's Horizon 2020 research and innovation program, Green Deal, European Commission, contract 101036245) . RI-URBANS is implementing the ACTRIS (https://actris.eu/) strategy for the development of services for improving air quality in Europe. The authors would like to also thank the support from "Agencia Estatal de Investigacion" from the Spanish Ministry of Science and Innovation under the project CAIAC (PID2019-108990RB-I00) and the Generalitat de Catalunya (AGAUR, SGR-447) M. Savadkoohi would like to thank the Spanish Ministry of Science and Innovation for her FPI grant (PRE-2020-095498) . This study is also part funded by the National Institute for Health Research (NIHR) Health Protection Research Unit in Environmental Exposures and Health, a partnership between UK Health Security Agency (UKHSA) and Imperial College London, and the UK Natural Environment Research Council. The views expressed are those of the author (s) and not necessarily those of the NIHR, UKHSA or the Department of Health and Social Care. The measurements in Stockholm (SE) were funded by the Swedish Environmental Protection Agency. The work performed in Rome (IT) was supported by ARPA Lazio, the regional Environmental Protection Agency.This work was also carried out through the Core Program within the Romanian National Research Development and Innovation Plan 2022-2027, with the support of MCID, project no. PN 23 05 and through the European Regional Development Fund through the Competitiveness Operational Programme 2014-2020, Action 1.1.3 Creating synergies with H2020 Programme, project Strengthen the participation of the ACTRIS-RO consortium in the pan-European research infrastructure ACTRIS, ACTRIS-ROC, MYSMIS code 107596 (ctr. no.337/2021) . Measurements at Granada urban station were possible thanks to the "Agencia Estatal de Investigacion" from the Spanish Ministry of Science and Innovation under the projects PID2020-120015RB-I00 and PID2021-128757OB-I00, and ACTRIS-Espana (CGL2017-90884REDT) . Measurements at Burjassot Atmospheric Station are supported by the Spanish Ministry of Economy and Competitiveness (MINECO) though the projects: RTI2018-096548-B-I00, PID2021-123881OB-I00 and TED2021-129185B-I00; and the Valencia Autonomous Government project: AICO/2021/341. IMT Nord Europe acknowledges financial support from the Labex CaPPA project, which is funded by the French National Research Agency (ANR) through the PIA (Programme d'In-vestissement d'Avenir) under contract ANR-11-LABX-0005-01, and the CLIMIBIO and ECRIN projects, both financed by the Regional Council "Hauts-de-France" and the European Regional Development Fund (ERDF) . The ATOLL site is one of the French ACTRIS National Facilities and contributes to the CARA program of the LCSQA funded by the French Ministry of Environment.This study analyzed the variability of equivalent black carbon (eBC) mass concentrations and their sources in urban Europe to provide insights into the use of eBC as an advanced air quality (AQ) parameter for AQ standards. This study compiled eBC mass concentration datasets covering the period between 2006 and 2022 from 50 measurement stations, including 23 urban background (UB), 18 traffic (TR), 7 suburban (SUB), and 2 regional background (RB) sites. The results highlighted the need for the harmonization of eBC measurements to allow for direct comparisons between eBC mass concentrations measured across urban Europe. The eBC mass concentrations exhibited a decreasing trend as follows: TR > UB > SUB > RB. Furthermore, a clear decreasing trend in eBC concentrations was observed in the UB sites moving from Southern to Northern Europe. The eBC mass concentrations exhibited significant spatiotemporal heterogeneity, including marked differences in eBC mass concentration and variable contributions of pollution sources to bulk eBC between different cities. Seasonal patterns in eBC concentrations were also evident, with higher winter concentrations observed in a large proportion of cities, especially at UB and SUB sites. The contribution of eBC from fossil fuel combustion, mostly traffic (eBCT) was higher than that of residential and commercial sources (eBCRC) in all European sites studied. Nevertheless, eBCRC still had a substantial contribution to total eBC mass concentrations at a majority of the sites. eBC trend analysis revealed decreasing trends for eBCT over the last decade, while eBCRC remained relatively constant or even increased slightly in some cities.RI-URBANS project (Research Infrastructures Services Reinforcing Air Quality Monitoring Capacities in European Urban amp; Industrial Areas)Horizon 2020Green DealEuropean Union (EU) European Commission Joint Research CentreAgencia Estatal de InvestigacionSpanish Ministry of Science and Innovation under the project CAIACAgencia de Gestio D'Ajuts Universitaris de Recerca Agaur (AGAUR) Generalitat de CatalunyaSpanish Ministry of Science and Innovation for her FPINational Institute for Health Research (NIHR) Health Protection Research Unit in Environmental Exposures and HealthSwedish Environmental Protection AgencyARPA LazioEnvironmental Protection AgencyCore Program within the Romanian National Research Development and Innovation PlanMCID 101036245European Regional Development Fund through the Competitiveness Operational ProgrammeH2020 Programme, project Strengthen the participation of the ACTRIS-RO PID2019-108990RB-I00European research infrastructure ACTRIS SGR-447ACTRIS-ROC PRE-2020-095498MYSMISSpanish Ministry of Science and Innovation under the projectsACTRIS-EspañaLabex CaPPA projectAgence Nationale de la Recherche (ANR) 2022-2027CLIMIBIO PN 23 05ECRIN projects 2014-2020Regional Council "Hauts-de-France"European Union (EU)French Ministry of Environment107596, 337/2021, PID2020-120015RB-I00, PID2021-128757OB-I00, AICO/2021/341, ANR-11-LABX-0005-0

Contribution to column-integrated aerosol typing based on Sunphotometry using different criteria

This study analyses the aerosol optical and microphysical properties obtained by the Aerosol Robotic Network (AERONET) in seven different sites operating in the Iberian Peninsula during three coincident years (2010−2012) with the objective of studying different aerosol typing approaches. This area is of interest due to its location between the Sahara desert (the largest source of natural aerosols in the world) and mainland Europe (a relevant source of anthropogenic aerosols). In particular, we study the aerosol optical depth (AOD), Angström parameter (α440–870) and fine mode fraction (FMF), which are estimated from direct sun irradiance measurements. Additionally, the single scattering albedo (ωo) and aerosol particle size distribution (PSD), which are computed using additional sky radiances measurements under cloudless skies, are used in our analyses. The analyses show aerosol seasonal patterns in the AOD with maximum values in summer/spring and minimum values in winter/autumn for all the analysed stations. For α440–870, there are differences from site to site, with maximum values in winter and minimum values in summer for the southern locations, while there is not a remarkable pattern for the eastern locations close to the Mediterranean coast. The frequent and intense Saharan dust outbreaks over the southern Iberian Peninsula and the intense anthropogenic activity in the eastern urban locations are behind these seasonal patterns in the AOD and α440–870. In this work, two of the most employed classification schemes of aerosol type in the literature are used: one is based on the AOD and α440–870, the other one is based on ωo at 440 nm and the FMF and a new classification scheme based on ωo at 440 nm and FMF is proposed. The results revealed that the new classification method is more appropriate for distinguishing the aerosol types that affect the Iberian Peninsula. The relationship derived here between Δωo = ωo (440)- ωo (1020) and the FMF is demonstrated to be useful for aerosol type classification when no measurements of the sky radiances, and consequently of ωo(440), are available. Alternatively, the relationship between the ratio Δωo/ωo(440) and the FMF can be used because (Δωo/ωo) provides information about both the spectral ωo and the absolute values.Spanish Ministry of Economy and Competitiveness through projects CGL2013-45410-RSpanish Ministry of Economy and Competitiveness through projects CGL2016-81092-RSpanish Ministry of Economy and Competitiveness through projects CGL2017-90884-REDTAndalusia Regional Government through projects P12-RNM-240

Physical and optical properties of aerosols over an urban location in Spain: seasonal and diurnal variability

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<particle diameter<1 μm) is significantly larger than in summer while the number density of "coarse" particles (1<particle diameter<20 μm) is slightly larger during summer and spring than during winter and autumn. The scattering Angström exponent, αs, presents an evident seasonal cycle with values of 1.8±0.2, 1.6±0.3, 1.3±0.3 and 1.4±0.3 in winter, spring, summer and autumn, respectively. This suggests the presence of a large fraction of submicron particles at the site, especially during winter. The aerosols measured in this study contain a large fraction of absorbing material as indicated by the average single-scattering albedo that has values of 0.65±0.07, 0.66±0.06, 0.70±0.06 and 0.73±0.06 in autumn, winter, spring and summer, respectively. The aerosol scattering albedo obtained in the surface boundary layer of Granada is below the critical value of 0.86 that determines the shift from cooling to warming. These results put in evidence the need of efforts to reduce absorbing particles (black carbon) emissions to avoid the possible warming that would result from the reductions of the cooling aerosols only. The aerosol absorption and scattering coefficients present a clear diurnal pattern, in all seasons, with two local maxima, one early in the morning and the second one in the evening. This diurnal cycle is mainly attributed to the diurnal evolution of atmospheric boundary layer and local anthropogenic activities.This work was supported by the Spanish Ministry of Science and Technology through projects No: CGL2007-66477-C02-01 and CSD2007-00067 and by the Andalusian Regional Government through projects No: P06-RNM-01503 and P08-RNM-3568

A global view on the effect of water uptake on aerosol particle light scattering

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

Wind and Turbulence Statistics in the Urban Boundary Layer over a Mountain–Valley System in Granada, Spain

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 FPU14/03684Ministerio de Asusntos Economicos y Transformacion Digital CGL2016-81092-R CGL2017-83538-C3-1-R CGL2017-90884-REDT PID2020-120015RB-I00 PID2020.117825GB.C21Junta de Andalucia A-RNM-430-UGR20 P18-RT-3820 P20-00136Horizon 2020 Framework Programme of the European Union 654109European Cooperation in Science and Technology (COST) ES1303 CA18235Erasmus + Programme of the European UnionFundacion Ramon ArecesPolish National Science Centre (NCN) 2021/40/C/ST10/00023Excellence Units Program of the University of Granada 'Programa 7' of 'Plan Propio' of the University of Granad

Multi-exposure adaptive threshold technique for cloud detection with sky imagers

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)

Carbonaceous Particles in the Atmosphere: Experimental and Modelling Issues

Carbonaceous particles and their organic component are one of the major combustion by-products and they are recognized to play a relevant role in radiative transfer, air quality, and human health, due to their fine-submicrometric nature. These effects are magnified by transboundary air masses transport of natural fires plumes or anthropogenic emissions from domestic heating and industrial activities, affecting not only the source areas. In fact, analysis on snow samples from different arctic sites revealed the presence of carbonaceous particulate matter, with biomass burning identified as responsible for more than 90% of these particles. As a consequence of this deposition, snow albedo variations are added to the other factors influencing Earth’s radiative budget. For these reasons, there is a growing interest toward the above-mentioned arguments, but there is also a need to assess the role of carbonaceous particles and to review the different measurements techniques, highlighting their limitations and uncertainties. The papers included in this special issue improve the comprehension of processes involving carbonaceous particles considering them under different points of view because both experimental and modeling approaches are examined