Phenomenology of High-Ozone Episodes in NE Spain
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Atmos. Chem. Phys., 17, 2817–2838, 2017 www.atmos-chem-phys.net/17/2817/2017/ doi:10.5194/acp-17-2817-2017 © Author(s) 2017. CC Attribution 3.0 License. Phenomenology of high-ozone episodes in NE Spain Xavier Querol1, Gotzon Gangoiti2, Enrique Mantilla3, Andrés Alastuey1, Maria Cruz Minguillón1, Fulvio Amato1, Cristina Reche1, Mar Viana1, Teresa Moreno1, Angeliki Karanasiou1, Ioar Rivas1, Noemí Pérez1, Anna Ripoll1, Mariola Brines1, Marina Ealo1, Marco Pandolfi1, Hong-Ku Lee4, Hee-Ram Eun4, Yong-Hee Park4, Miguel Escudero5, David Beddows6, Roy M. Harrison6,a, Amelie Bertrand7, Nicolas Marchand7, Andrei Lyasota8,†, Bernat Codina8, Miriam Olid8, Mireia Udina8, Bernat Jiménez-Esteve8, María R. Soler8, Lucio Alonso2, Millán Millán3, and Kang-Ho Ahn4 1Institute of Environmental Assessment and Water Research, IDAEA-CSIC, C/Jordi Girona 18–26, 08034 Barcelona, Spain 2Escuela Técnica Superior Ingeniería de Bilbao, Departamento Ingeniería Química y del Medio Ambiente, Universidad del País Vasco UPV/EHU, Urkixo Zumarkalea, S/N, 48013 Bilbao, Spain 3Centro de Estudios Ambientales del Mediterráneo, CEAM, Unidad Asociada al CSIC, Parque Tecnológico C/Charles R. Darwin, 14 46980 Paterna, Valencia, Spain 4Department of Mechanical Engineering, Hanyang University, Ansan 425-791, Republic of Korea 5Centro Universitario de la Defensa de Zaragoza, Academia General Militar, Ctra. de Huesca s/n, 50090 Zaragoza, Spain 6Division of Environmental Health & Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 7Aix Marseille Univ, CNRS, LCE, 13331 Marseille, France 8Department of Astronomy and Meteorology, Faculty of Physics, University of Barcelona, Martí I Franquès 1, 08028 Barcelona, Spain aalso at: Department of Environmental Sciences/Centre for Excellence in Environmental Studies, King Abdulaziz University, Jeddah, Saudi Arabia †deceased Correspondence to: Xavier Querol ([email protected]) and Kang-Ho Ahn ([email protected]) Received: 14 October 2016 – Discussion started: 10 November 2016 Revised: 17 January 2017 – Accepted: 23 January 2017 – Published: 23 February 2017 Abstract. Ground-level and vertical measurements (per- tions of both O3 and precursors. These processes gave rise formed using tethered and non-tethered balloons), coupled to maximal O3 levels in the inland plains and valleys north- with modelling, of ozone (O3/, other gaseous pollutants wards from the BMA when compared to the higher moun- (NO, NO2, CO, SO2/ and aerosols were carried out in the tain sites. Thus, a maximum O3 concentration was observed plains (Vic Plain) and valleys of the northern region of the within the lower tropospheric layer, characterised by an up- Barcelona metropolitan area (BMA) in July 2015, an area ward increase of O3 and black carbon (BC) up to around −3 typically recording the highest O3 episodes in Spain. Our 100–200 m a.g.l. (reaching up to 300 µg m of O3 as a 10 s results suggest that these very high O3 episodes were orig- average), followed by a decrease of both pollutants at higher inated by three main contributions: (i) the surface fumigation altitudes, where BC and O3 concentrations alternate in lay- from high O3 reservoir layers located at 1500–3000 m a.g.l. ers with parallel variations, probably as a consequence of the (according to modelling and non-tethered balloon measure- atmospheric transport from the BMA and the return flows ments), and originated during the previous day(s) injections (to the sea) of strata injected at certain heights the previous of polluted air masses at high altitude; (ii) local/regional pho- day(s). At the highest altitudes reached in this study with the tochemical production and transport (at lower heights) from tethered balloons (900–1000 m a.g.l.) during the campaign, the BMA and the surrounding coastal settlements, into the BC and O3 were often anti-correlated or unrelated, possibly inland valleys; and (iii) external (to the study area) contribu- due to a prevailing regional or even hemispheric contribution Published by Copernicus Publications on behalf of the European Geosciences Union. 2818 X. Querol et al.: Phenomenology of high-ozone episodes in NE Spain −3 of O3 at those altitudes. In the central hours of the days a – A population alert hourly threshold of 240 µg m . homogeneous O distribution was evidenced for the lowest 3 – A vegetation protection target, AOT40 (expressed in 1 km of the atmosphere, although probably important varia- µg m−3 h), as the sum of the excess of hourly concen- tions could be expected at higher levels, where the high O 3 trations above 80 µg m−3 in a given period using hourly return strata are injected according to the modelling results values measured between 08:00 and 20:00, Central Eu- and non-tethered balloon data. rope Time (CET), for every day. Hourly AOT40 from Relatively low concentrations of ultrafine particles (UFPs) May to July should not exceed 18 000 µg m−3 h O as a were found during the study, and nucleation episodes were 3 5-year mean. only detected in the boundary layer. Two types of O3 episodes were identified: type A with ma- NOx has a catalytic effect in O3 generation, and is only −3 jor exceedances of the O3 information threshold (180 µg m removed from the system by either deposition or oxida- on an hourly basis) caused by a clear daily concatena- tion to nitric acid (HNO3/ and reaction with VOCs to yield tion of local/regional production with accumulation (at up- secondary aerosols, such as inorganic and organic nitrates, per levels), fumigation and direct transport from the BMA which may sequester a significant fraction of NOx. Conse- (closed circulation); and type B with regional O3 production quently, O3 generation involves not only local and regional without major recirculation (or fumigation) of the polluted air masses but also long-range transport. Thus, as a general BMA/regional air masses (open circulation), and relatively observation, long-range transport of O3 and its precursors in- lower O3 levels, but still exceeding the 8 h averaged health fluence markedly the background O3 levels in Europe (UN- target. ECE, 2010; Doherty et al., 2013). However, this situation To implement potential O3 control and abatement strate- might be very different when considering the high summer gies two major key tasks are proposed: (i) meteorological O3 episodes of southern Europe (e.g. Millán et al., 1997, forecasting, from June to August, to predict recirculation 2000; Palacios et al., 2002; Castell et al., 2008a, b, 2012; episodes so that NOx and VOC abatement measures can be Stein et al., 2005; Escudero et al., 2014; Pay et al., 2014; applied before these episodes start; (ii) sensitivity analysis Querol et al., 2016). with high-resolution modelling to evaluate the effectiveness In the western Mediterranean Basin the problem of tropo- of these potential abatement measures of precursors for O3 spheric O3 has been intensively studied since the early 1980s reduction. (Millán et al., 1991, 1996a, b, c, 2000, 2002; Millán, 2002; Millán and Sanz, 1999; Mantilla et al., 1997; Salvador et al., 1997, 1999; Gangoiti et al., 2001; Stein et al., 2004, 2005; 1 Introduction Dieguez et al., 2009, 2014; Doval et al., 2012; Castell et al., 2008a, b, 2012; Escudero et al., 2014). Results have evi- Ozone (O3/ is an airborne secondary pollutant that is denced that (i) the meteorology driving O3 fluctuation in this produced through the photo oxidation of volatile organic region is markedly influenced by a very complex orography, compounds (VOCs) in the presence of nitrogen oxides with high mountain chains surrounding the basin; (ii) in sum- (NOx D NO C NO2/, with more intensive production in high mer, the lack of a marked synoptic advection caused by the insolation regions. It is well known that its formation pro- presence of the Azores anticyclone and the Iberian and North cesses are very complex and that the reaction and produc- African thermal lows, together with the sea and land breezes, tion rates are not linear (Monks et al., 2015, and references give rise to air mass recirculation episodes (lasting for several therein). According to EEA (2015), 97 % of the European days); and (iii) during these summer vertical and horizontal population is exposed to O3 concentrations that exceed the recirculations of air masses loaded with O3 precursors and WHO guideline (see below) for the protection of human coinciding with high insolation and elevated biogenic VOCs health. The complexity of this pollutant is also reflected in (BVOCs) emissions (Seco et al., 2011), high O3 concentra- its air quality targets; thus, the European air quality directive tions may be recorded. 2008/50/EC establishes a number of O3 target values (which Millán’s team results demonstrated that western Mediter- are not legally binding, as opposed to the limit values set for ranean Basin dynamics are very different from those in cen- the majority of pollutants): tral Europe. The latter are dominated by neutral-cloudy con- ditions, where O episodes are usually associated with ad- – A human health target value fixed at 120 µg m−3 as 8 h 3 vection, and transformation takes place within large displace- maximum in a day that should not be exceeded more ments of air masses. There, morning fumigation from a high than 25 days in a year as a 3-year mean. This target O residual (and stratified) boundary layer (BL) formed over value was (arbitrarily) increased from the recommended 3 the previous days, in addition to local formation in the sunny 100 µg m−3 in the WHO air quality guidelines (where midday period may give rise to peak O episodes if condi- no specific number of exceedances is recommended). 3 tions persist after several days. In contrast, vertical recircula- – A population information hourly threshold of tions developed over all western Mediterranean coastal areas, −3 180 µg m .