The Solar Radiation Group of Valencia (GRSV) is a reference group in the two lines in which it works, atmospheric aerosols and solar UV radiation, and is considered a Group of Excellence of the Valencian Community through the Prometheus 2010 and Prometheus 2014 Projects, granted by the Generalitat Valenciana. The Solar Radiation Group has participated in numerous field campaigns, from Sodankyla (Finland) to Marrakesh (Morocco), including those carried out by the ESA (European Space Agency) in the Barrax area (Albacete), during 1998, 1999 and 2000 (DAISEX I and II, Digital Airbone Imaging Spectrometer EXperiment), 2003 and 2004 (SPARC, SPectra bARrax Campaign) and 2005 (SEN2FLEX, SENtinel-2 and Fluorescence Experiment).

It has coordinated the thematic networks DAMOCLES "Determination of Aerosols by Column Measurements (Lidar), Extinction and Soil" I and II during the years 2004 to 2010, in which more than thirty Spanish Institutions have participated. In recent years the GRSV has participated in the SAVEX (Sunphotometer Airborne Validation Experiment) campaigns which took place in June 2012 in Tenerife and the western region of the Sahara. This campaign consisted of the measurement of aerosol properties during a Saharan intrusion (mineral dust, of great climatic importance). The interest lay in the simultaneous measurement of properties using CIMEL CE318 (whose data were developed by AERONET) and PREDE POM (whose data were developed by ESR-SKYNET) instruments for comparison and validation with vertical profile measurements obtained with instruments installed on board an aircraft.

Different European groups were involved in this campaign, mainly from the UK MetOffice, the University of Reading (UK) and the Consiglio Nazionalle delle Ricerche (Italy). This campaign was carried out in the framework of the DA-SAVEX project, awarded in the pre-competitive programme of the University of La Laguna, and also supported to a large extent by the UK MetOffice, which provided the necessary aerial means and the instrumentation on board the aircraft. It has also participated in the Sunphotometer Airborne Validation Experiment in Dust - SAVEX/D campaign in April 2017 (http://pre-tect.space.noa.gr) and CHemistry and AeRosols Mediterranean EXperiment (ChArMEx; http://charmex.lsce.ipsl.fr), which is a collaborative research programme that introduces international activities to investigate Regional Interactions of Mediterranean Chemistry and Climate. The Solar Radiation group currently participates in the international aerosol measurement network AErosol RObotic NETwork (AERONET, https://aeronet.gsfc.nasa.gov/).

The AERONET programme is a federation of ground-based aerosol networks established by NASA and PHOTONS (PHOtométrie pour le Traitement Opérationnel de Normalisation Satellitaire; Univ. De Lille 1, CNES and CNRS-INSU) and extended through other networks such as RIMA (Red Ibérica de Medida de Aerosoles), AeroSpan, AEROCAN and CARSNET with national agencies, institutes and universities as partners.

The programme provides a public domain database of optical, microphysical and radiative properties of aerosols for aerosol research and characterisation, satellite validation and synergy with other databases. The Solar Radiation group has two stations (Burjassot and Aras de los Olmos) that are part of this AERONET network and actively collaborate with other Spanish stations of the RIMA Network in its operation. In addition, the GRSV also coordinates the European Skynet Radiometers network (ESR, http://www.euroskyrad.net/) together with the Institute of Atmospheric Sciences and Climate of the Italian National Research Council (CNR). In this network, whose scientific objective is also the characterisation of atmospheric aerosols and their interaction with clouds and solar radiation, as well as the validation of satellite products, several European Universities/Meteorological Services from Italy, Germany, UK, Chile, as well as the NREL in the USA participate.

In addition, the GRSV is an Associated Partner in the ACTRIS2 (Aerosols, Clouds, and Trace gases Research InfraStructure Network) (www.actris.eu), a European research infrastructure (RI) funded under the H2020 programme in the context of Climate Change. The network has been accepted in the ESFRI (The European Strategy Forum on Research Infrastructure) roadmap in 2016. This means that the ACTRIS network is set up as a pan-European research infrastructure that will be consolidated and operational over the next ten years. The ACTRIS project involves 28 European organisations and aims to establish a network of stable scientific infrastructures equipped with advanced instrumentation for the measurement of atmospheric aerosols, gases and clouds. 
They also participate in the ACTRIS-SPAIN thematic network (CGL2017-90884-REDT) which is developing research on the direct and indirect effects of aerosols and clouds, as well as on the processes associated with atmospheric pollutants that are involved in the deterioration of air quality causing adverse effects on health and ecosystems.

ACTRIS-SPAIN will also contribute to the development of sustainable solutions to environmental challenges and thus fits perfectly into the overall objectives of ACTRIS. In this network, work is being carried out during this final quarter of 2020 to transform the Memorandum of Understanding that exists between the participants in this network and AEMET, which participates in it as an external entity, into a Joint Research Unit (JRU), operational at European level, through an agreement between the entities adapted to Law 40/2015 on the Legal Regime of the Public Sector. ACTRIS-SPAIN members currently participate as beneficiaries, third parties, or associated participants, in the H2020 project of preparatory phase for the implementation of European research infrastructures ACTRIS-PPP (Grant Agreement no. 739530).

Our group also participates in European projects within the framework of the H2020 programme. Specifically, in the EMPIR-Environment call (European Metrology Programme for Innovation and Research co-funded by the H2020 programme) of EURAMET (European Metrology Networks). The project is entitled Metrology of Aerosol Optical Properties (MAPP) and aims to study the traceability of aerosol measurements in the atmospheric column, and the estimation of the uncertainty of the products offered by the different international measurement networks has been accepted and will be developed in the years 2020 - 2023 by a consortium that includes different leading Spanish and European laboratories, such as the Lille Laboratory of Atmospheric Optics (LOA, France), National Research Centre (CNRS, France), Italian National Research Council (CNR, Italy), Spanish Meteorological Agency (AEMET, Spain), University of Reading (URE, UK), University of Valladolid (UVa, Spain). The project is coordinated by the Schweizerisches Forschungsinstitut für Hochgebirgsklima und Medizin (SFI Davos, Switzerland) and in Valencia the PI in charge is Victor Estellés, member of the team requesting the project.

The main lines of research of the GRSV are:

• Atmospheric aerosols and clouds.
• Characterisation of atmospheric aerosols from extinction measurements of solar irradiance and sky radiance.
• Dependence of atmospheric aerosols on the origin of air masses.
• Inversion methods to determine aerosol size distributions.
• Dynamic analysis of aerosol hygroscopic growth.
• Relationship of Angstrom coefficients with aerosol characteristics.
• Remote sensing applications. Atmospheric correction.
• Determination of the atmospheric profile of aerosols using lidar techniques.
• Measurement of cloud radiative properties.
• Study of the radiative forcing of atmospheric aerosols.
• Study of aerosol-cloud interactions and their radiative effects.
• Solar Ultraviolet radiation.
• Effects of UVB radiation on humans.
• UVI (UltraViolet Index) prediction.
• Solar simulators for use in clinical dermatology.
• Spectral and integrated measurement of solar UV radiation.
• Modelling of the direct and diffuse components of solar UV radiation.
• Modelling of solar UV radiation on inclined planes.
• Measurements of solar UVB radiation and prediction of erythemal solar UV radiation under clear and cloudless skies.

Investigation activities