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This study aimed to investigate the causes of contrasting ozone (O3) trends in Spanish O3 hotspots between 2008 and 2019, as documented in recent studies. The analysis involved data on key O3 precursors, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), among other species, along with meteorological parameters associated with O3. The dataset comprised ground-level and satellite observations, emissions inventory estimates, and meteorological reanalysis. The results suggest that the increasing O3 trends observed in the Madrid area were mostly due to major decreases in NOx emissions from the road transport sector in this urban VOC-limited environment, as well as variations in meteorological parameters conducive to O3 production. Conversely, the decreasing O3 trends in the Sevilla area likely resulted from a decrease in NOx emissions in a peculiar urban NOx-limited regime caused by substantial VOC contributions from a large upwind petrochemical area. Unchanged O3 concentrations in other NOx-limited hotspots may be attributed to the stagnation of emissions from sectors other than road transport, coupled with increased emissions from certain sectors, likely due to the economic recovery from the 2008 financial crisis, and the absence of meteorological variations favorable to O3 production. In this study, the parameters influencing O3 varied distinctively across the different hotspots, emphasizing the significance of adopting an independent regional/local approach for O3 mitigation planning. Overall, our findings provide valuable insights into the causes of contrasting O3 trends in different regions of Spain, which can be used as a basis for guiding future measures to mitigate O3 levels., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The present work was supported by the Spanish Ministry of Ecological Transition and Demographic Challenge (Spanish National Ozone Plan); European Union’s Horizon 2020 research and innovation program under grant agreement; the “Agencia Estatal de Investigación,” from the Spanish Ministry of Science and Innovation, and FEDER funds under the project CAIAC (PID2019-108990RB-I00); the Generalitat de Catalunya (AGAUR 2021 SGR 00447); and the Ministerio de Ciencia e Innovación through the MITIGATE project (grant no. PID2020-113840RA-I00 funded by MCIN/AEI/10.13039/501100011033). This work was also supported by the Autonomous Government of Valencia (GVA) through the Valencian Institute for Business Competitiveness (IVACE) by means of the project Gaia (IMAMCA/2022/1). Carlos Pérez García-Pando acknowledges the support of the AXA Research Fund. We would like to thank NASA and the QA4ECV project for providing satellite-based data and the Climate Data Store (CDS) from the Copernicus Program for the ERA5 meteorological data., Peer Reviewed, Postprint (published version)

Pòster amb el resum gràfic de la tesi doctoral en curs, que forma part de l'exposició "Doctorat en Recursos Naturals i Medi Ambient de la UPC Manresa. 30 anys formant en recerca a la Catalunya Central 1992-2022"., Postprint (published version)

This global study, which has been coordinated by the World Meteorological Organization Global Atmospheric Watch (WMO/GAW) programme, aims to understand the behaviour of key air pollutant species during the COVID-19 pandemic period of exceptionally low emissions across the globe. We investigated the effects of the differences in both emissions and regional and local meteorology in 2020 compared with the period 2015–2019. By adopting a globally consistent approach, this comprehensive observational analysis focuses on changes in air quality in and around cities across the globe for the following air pollutants PM2.5, PM10, PMC (coarse fraction of PM), NO2, SO2, NOx, CO, O3 and the total gaseous oxidant (OX = NO2 + O3) during the pre-lockdown, partial lockdown, full lockdown and two relaxation periods spanning from January to September 2020. The analysis is based on in situ ground-based air quality observations at over 540 traffic, background and rural stations, from 63 cities and covering 25 countries over seven geographical regions of the world. Anomalies in the air pollutant concentrations (increases or decreases during 2020 periods compared to equivalent 2015–2019 periods) were calculated and the possible effects of meteorological conditions were analysed by computing anomalies from ERA5 reanalyses and local observations for these periods. We observed a positive correlation between the reductions in NO2 and NOx concentrations and peoples’ mobility for most cities. A correlation between PMC and mobility changes was also seen for some Asian and South American cities. A clear signal was not observed for other pollutants, suggesting that sources besides vehicular emissions also substantially contributed to the change in air quality. As a global and regional overview of the changes in ambient concentrations of key air quality species, we observed decreases of up to about 70% in mean NO2 and between 30% and 40% in mean PM2.5 concentrations over 2020 full lockdown compared, Peer Reviewed, Article signat per 97 autors: Ranjeet S. Sokhi, Vikas Singh, Xavier Querol, Sandro Finardi, Admir Créso Targino, Maria de Fatima Andrade, Radenko Pavlovic, Rebecca M. Garland, Jordi Massagué, Shaofei Kong, Alexander Baklanov, Lu Ren, Oksana Tarasova, Greg Carmichael, Vincent-Henri Peuch, Vrinda Anand, Graciela Arbilla, Kaitlin Badali, Gufran Beig, Luis Carlos Belalcazart, Andrea Bolignano, Peter Brimblecombe, Patricia Camacho, Alejandro Casallas, Jean-Pierre Charland, Jason Choi, Eleftherios Chourdakis, Isabelle Coll, Marty Collins, Josef Cyrys, Cleyton Martins da Silva, Alessandro Domenico Di Giosa, Anna Di Leo, Camilo Ferro, Mario Gavidia-Calderon, Amiya Gayen, Alexander Ginzburg, Fabrice Godefroy, Yuri Alexandra Gonzalez, Marco Guevara-Luna, Sk. Mafizul Haque, Henno Havenga, Dennis Herod, Urmas Horrak, Tareq Hussein, Sergio Ibarra, Monica Jaimes, Marko Kaasik, Ravindra Khaiwal, Jhoon Kim, Anu Kousa, Jaakko Kukkonen, Markku Kulmala, Joel Kuular, Nathalie La Violette, Guido Lanzani, Xi Liu, Stephanie MacDougall, Patrick M. Manseau, Giada Marchegiani, Brian McDonald, Swasti Vardhan Mishra, Luisa T. Molina, Dennis Mooibroek, Suman Mor, Nicolas Moussiopoulos, Fabio Murena, Jarkko V. Niemi, Steffen Noe, Thiago Nogueira, Michael Norman, Juan Luis Pérez-Camano, Tuukka Petaj, Stuart Piketh, Aditi Rathod, Ken Reid, Armando Retama, Olivia Rivera, Néstor Y. Rojast, Jhojan P. Rojas-Quincho, Roberto San José, Odon Sanchez, Rodrigo J. Seguel, Salla Sillanpaa, Yushan Su, Nigel Tapper, Antonio Terrazas, Hilkka Timonen, Domenico Toscano, George Tsegas, Guus J.M. Velders, Christos Vlachokostas, Erika von Schneidemesseri, Rajasree VPM, Ravi Yadav, Rasa Zalakeviciute, Miguel Zavala, Postprint (published version)

The Guadalquivir Valley is one of three major O3 hotspots in Spain. An airborne and surface measurement campaign was carried out from July 9th to 11th, 2019 to quantify the local/regional O3 contributions using experimental approaches. Air quality and meteorology data from surface measurements, a microlight aircraft, a helium balloon, and remote sensing data (TROPOMI-NO2-ESA) were used to obtain the 3D distribution of O3 and various tracer pollutants. O3 accumulation over 2.5 days started with inputs from oceanic air masses transported inland by sea breezes, which drew O3 and its precursors from a local/regional origin to the northeastern end of the basin. The orographic–meteorological setting of the valley caused vertical recirculation of the air masses inside the valley that caused the accumulation by increasing regional background O3 concentration by 25–30 ppb. Furthermore, possible Mediterranean O3 contributions and additional vertical recirculation through the entrainment zone of the convective boundary layer also contributed. Using particulate matter finer than 2.5 µm (PM2.5), ultrafine particles (UFP), and black carbon (BC) as tracers of local sources, we calculated that local contributions increased regional O3 levels by 20 ppb inside specific pollution plumes transported by the breeze into the valley, and by 10 ppb during midday when flying over an area with abundant agricultural burning during the morning. Air masses that crossed the southern boundaries of the Betic system at mid-altitude (400–1850 m a.s.l.) on July 10th and 11th may have provided additional O3. Meanwhile, a decreasing trend at high altitudes (3000–5000 m a.s.l.) was observed, signifying that the impact of stratospheric O3 intrusion decreased during the campaign., The present work was supported by the Spanish Ministry for Ecological Transition (17CAES010); the “Agencia Estatal de Investigación” from the Spanish Ministry of Science, Innovation and Universities and FEDER funds under the project HOUSE (CGL2016-78594-R); the Agencia Estatal de Investigación (RTI2018-095937-B-I00); and the Generalitat de Catalunya (AGAUR 2017 SGR41). We would like to thank the Junta de Andalucía for providing us with air quality data, and the Spanish Met Office (AEMET) for providing meteorological data and facilitating staff and instrumentation for the soundings, as well as ESA for providing TROPOMI-NO2 data and NOAA for the HYSPLIT modeling tool. Cristina Carnerero thanks “Agencia Estatal de Investigación” for the grant received to carry out her PhD (FPI grant: BES-2017-080027). Carlos Pérez García-Pando acknowledges support by the AXA Research Fund, and the Spanish Ministry of Science, Innovation and Universities (RYC-2015-18690)., Peer Reviewed, Postprint (published version)

We offer an overview of the COVID-19 -driven air quality changes across 11 metropolises in Spain with the focus on lessons learned on how continuing abating pollution. Traffic flow decreased by up to 80% during the lockdown and remained relatively low during the full relaxation (June and July). After the lockdown a significant shift from public transport to private vehicles (+21% in Barcelona) persisted due to the pervasive fear that using public transport might increase the risk of SARS-CoV-2 infection, which need to be reverted as soon as possible. NO2 levels fell below 50% of the WHO annual air quality guidelines (WHOAQGs), but those of PM2.5 were reduced less than expected due to the lower contributions from traffic, increased contributions from agricultural and domestic biomass burning, or meteorological conditions favoring high secondary aerosol formation yields. Even during the lockdown, the annual PM2.5 WHOAQG was exceeded in cities within the NE and E regions with high NH3 emissions from farming and agriculture. Decreases in PM10 levels were greater than in PM2.5 due to reduced emissions from road dust, vehicle wear, and construction/demolition. Averaged O3 daily maximum 8-h (8hDM) experienced a generalized decrease in the rural receptor sites in the relaxation (June–July) with -20% reduced mobility. For urban areas O3 8hDM responses were heterogeneous, with increases or decreases depending on the period and location. Thus, after canceling out the effect of meteorology, 5 out of 11 cities experienced O3 decreases during the lockdown, while the remaining 6 either did not experience relevant reductions or increased. During the relaxation period and coinciding with the growing O3 season (June–July), most cities experienced decreases. However, the O3 WHOAQG was still exceeded during the lockdown and full relaxation periods in several cities. For secondary pollutants, such as O3 and PM2.5, further chemical and dispersion modeling along with source apportionment, The present work was supported by the Spanish Ministerio para la Transición Ecológica y Reto Demográfico (17CAES010), the “Agencia Estatal de Investigación” from the Spanish Ministry of Science and Innovation (IDAEA-CSIC is a Centre of Excellence Severo Ochoa CEX2018-000794-S), FEDER funds under the project CAIAC (PID2019- 108990RB-I00), and by the Generalitat de Catalunya (AGAUR 2017 SGR41). We would like to thank the Spanish Meteorological Office (AEMET) for providing meteorological data as well as NASA for providing OMI-NO2 data. BSC co-authors acknowledge the support of the Copernicus Atmosphere Monitoring Service (CAMS), which is implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Commission, the Ministerio de Ciencia, Innovación y Universidades (MICINN) (RTI2018-099894-BI00, CGL2017-88911-R), the Agencia Estatal de Investigación (PID2019-108086RA-I00/AEI/0.13039/501100011033), the AXA Research Fund, and PRACE and RES for awarding access to Marenostrum4 based in Spain at the Barcelona Supercomputing Center. H. Petetin also acknowledges the European Union's Horizon 2020 - Research and Innovation Framework Programme under the H2020 Marie Skłodowska-Curie Actions grant agreement H2020-MSCACOFUND-2016-754433., Peer Reviewed, Article signat per 20 autors/es: Xavier Querol (a), Jordi Massagué (a, b), Andrés Alastuey (a), Teresa Moreno (a), Gotzon Gangoiti (c), Enrique Mantilla (d), José Jaime Duéguez (d), Miguel Escudero (e), Eliseo Monfort (f), Carlos Pérez García-Pandog (h), Hervé Petetin (g), Oriol Jorba (g), Víctor Vázquez (i, j), Jesús de la Rosa (k), Alberto Campos (l), Marta Muñóz (l), Silvia Monge (l), María Hervás (l), Rebeca Javato (l), María J. Cornide (l) a- Institute of Environmental Assessment and Water Research, IDAEA-CSIC, Barcelona 08034, Spain b- Department of Mining, Industrial and ICT Engineering, Universitat Politècnica de Catalunya - BarcelonaTech (UPC), Manresa 08242, Spain c- Department of Chemical and Environmental Engineering, University of Basque Country, Leioa 48940, Spain d- Centro de Estudios Ambientales del Mediterráneo, CEAM, València 46980, Spain e- Centro Universitario de la Defensa, Academia General Militar, Zaragoza 50090, Spain f- Instituto de Tecnología Cerámica ITC-UJI, Castelló 12006, Spain g- Barcelona Supercomputing Center, BSC-CNS, Barcelona 08034, Spain h- ICREA, Catalan Institution for Research and Advanced Studies, Barcelona 08010, Spain i- Department of Ecology, Faculty of Sciences, University of Málaga, 29071 Málaga, Spain j- Department of Research and Development, Coccosphere Environmental Analysis, 29120 Málaga, Spain k- Department of Geology, University of Huelva, Unidad de Investigación Associada a IDAEA-CSIC, Huelva 21819, Spain l- D.G. Calidad y Evaluación Ambiental del Ministerio de Transición Ecológica y Reto Demográfico, Madrid 28071, Spain, Postprint (published version)

We analyzed 2005–2017 data sets on ozone (O3) concentrations in an area (the Vic Plain) frequently affected by the atmospheric plume northward transport of the Barcelona metropolitan area (BMA), the atmospheric basin of Spain recording the highest number of exceedances of the hourly O3 information threshold (180¿µg¿m-3). We aimed at evaluating the potential benefits of implementing local-BMA short-term measures to abate emissions of precursors. To this end, we analyzed in detail spatial and time variations of concentration of O3 and nitrogen oxides (NO and NO2, including OMI remote sensing data for the latter). Subsequently, a sensitivity analysis is done with the air quality (AQ) data to evaluate potential O3 reductions in the north of the BMA on Sundays compared with weekdays as a consequence of the reduction in regional emissions of precursors. The results showed a generalized decreasing trend for regional background O3 as well as the well-known increase in urban O3 and higher urban NO decreasing slopes compared with those of NO2. The most intensive O3 episodes in the Vic Plain are caused by (i) a relatively high regional background O3 (due to a mix of continental, hemispheric–tropospheric and stratospheric contributions); by (ii) intensive surface fumigation from mid-troposphere high O3 upper layers arising from the concatenation of the vertical recirculation of air masses; but also by (iii) an important O3 contribution from the northward transport/channeling of the pollution plume from the BMA. The high relevance of the local-daily O3 contribution during the most intense pollution episodes is clearly supported by the O3 (surface concentration) and NO2 (OMI data) data analysis. A maximum decrease potential (by applying short-term measures to abate emissions of O3 precursors) of 49¿µg¿O3¿m-3 (32¿%) of the average diurnal concentrations was determined. Structurally implemented measures, instead of episodically, could result in important additional O3 decreases bec, Peer Reviewed, Postprint (author's final draft)

Study of historical data series of surface air pollutants, atmospheric variables, NASA's OMI satellite records and others parameters to assess the phenomenology of high ozone pollution episodes at one of the most affected areas in Spain (Vic plain region)

Air quality trends and patterns in the coastal city of Santa Cruz de Tenerife (Canary Islands, Spain) for the period 2011–2015 were analyzed. The orographic and meteorological characteristics, the proximity to the African continent, and the influence of the Azores anticyclone in combination with the anthropogenic (oil refinery, road/maritime traffic) and natural emissions create specific dispersion conditions. SO2, NO2, PM10, PM2.5, and O3 pollutants were assessed. The refinery was the primary source of SO2; EU hourly and daily average limit values were exceeded during 2011 and alert thresholds were reached in 2011 and 2012. WHO daily mean guideline was occasionally exceeded. Annual averages in the three stations that registered the highest concentrations in 2011 and 2012 were between 9.3 and 20.4 µg/m3. The spatial analysis of SO2 concentrations with respect to prevailing winds corroborates a clear influence of the refinery to the SO2 levels. In 2014 and 2015, the refinery did not operate and the concentrations fell abruptly to background levels of 2.5–7.1 µg/m3 far below from WHO AQG. NO2 EU limit values, as well as WHO AQG for the period 2011–2015, were not exceeded. The progressive dieselization of the vehicle fleet caused an increment on NO2 annual mean concentrations (from 2011 to 2015) measured at two stations close to busy roads 25 to 31 µg/m3 (+21%) and 27 to 35 µg/m3 (+29%). NOx daily and weekly cycles (working days and weekends) were characterized. An anti-correlation was found between NOx and O3, showing that O3 is titrated by locally emitted NO. Higher O3 concentrations were reported because less NOx emitted during the weekends showing a clear weekend effect. Saharan dust intrusions have a significant impact on PM levels. After subtracting natural sources contribution, none of the stations reached the EU maximum 35 yearly exceedances of daily means despite seldom exceedances at some stations. None of the stations exceeded the annual mean EU limit values, Peer Reviewed, Postprint (published version)