Sub-continental transport mechanisms and pathways during two ozone episodes in northern Spain

Abstract

Abstract. Two ozone episodes (occurring in June 2001 and June 2003) in the air quality monitoring network of the Basque Country (BC) are analyzed. The population information threshold was exceeded in many stations (urban, urbanbackground and rural). During this type of episodes, forced by a blocking anticyclone over the British Isles, ozone background concentrations over the area increase after the import of pollution from both, the continental Europe and the western Mediterranean areas (Gangoiti et al., 2002). For the present analysis, emphasis is made in the search for transport mechanisms, pathways and area sources contributing to the build-up of the episodes. Contributions from a selection of 17 urban and industrial conglomerates in the western European Atlantic (WEA) and the western Mediterranean (WM) are shown after the results of a coupled RAMS-HYPACT modelling system. Meteorological simulations are tested against both the high-resolution wind data recorded at the BC coastal area by a boundary layer wind-profiler radar (Alonso et al., 1998) and the wind soundings reported by the National Centres of Meteorology at a selection of European and northAfrican sites. Results show that during the accumulation phase of the episodes, background ozone concentrations increase in the whole territory as a consequence of transport from the Atlantic coast of France and the British Channel. For the peak phase, intrusions from new sources, located at the Western Mediterranean, Southern France, Ebro Valley, and, occasionally, the area of Madrid are added, resulting in a further increase in the ozone concentrations. Direct day and night transport within the north-easterly winds over the sea from the WEA source region, and night-time transport within the residual layer over continental areas (southern France, the Ebro Valley, and central Iberia) modulate the import sequence of pollutants and the local increase of ozone concentrations. The alternative direct use of low resolution meteoCorrespondence to: G. Gangoiti (g.gangoiti@ehu.es) rological data for the estimation of back-trajectories shows a more simple transport scheme with no contributions neither from the Western Mediterranean nor from the Madrid area.

Ozone source apportionment during peak summer events over southwestern Europe

“…Southern European countries around the Mediterranean Basin are particularly exposed to exceedances of the O 3 target value in summer due to the influence of frequent anticyclonic and clear-sky conditions that favour photochemical O 3 formation in the troposphere (EEA, 2017). In addition, its geographic location also makes the basin a receptor of the long-range transport of pollution from Europe, Asia and even North America (Lelieveld et al, 2002;Gerasopoulos, 2005). The importance of long-range transport on surface O 3 has been studied in the Mediterranean Basin, indicating that the emission sources within the basin have a dominating influence on surface O 3 , whereas remote sources are more important than local sources for O 3 mixing ratios at higher altitudes (Richards et al, 2013;Safieddine et al, 2014).…”

“…Several studies in the Iberian Peninsula (IP) have addressed the causes of O 3 episodes by looking at the circulation of air masses (Millán, 2014, and references therein). In the Atlantic region, the blocking anticyclones over western Europe favour the inter-regional transport of O 3 in the area and its accumulation for several days during the most severe episodes (Alonso et al, 2000;Gangoiti et al, 2002Gangoiti et al, , 2006Valdenebro et al, 2011;Saavedra et al, 2012;Monteiro et al, 2016). Conversely, on the Mediterranean coast, the typical summer synoptic meteorological conditions with a lack of strong synoptic advection, combined with the orographic characteristics and the sea and land breezes, favour episodes where high levels of O 3 are accumulated by recirculation of air masses loaded with O 3 precursors (Millán et al, 1997(Millán et al, , 2000Toll and Baldasano, 2000;Gangoiti et al, 2001;Pérez et al, 2004;Jiménez et al, 2006;Gonçalves et al, 2009;Millán, 2014;Querol et al, 2017Querol et al, , 2018.…”

Trends of Rural Tropospheric Ozone at the Northwest of the Iberian Peninsula

“…In fact, most of the studies were centered in the Cantabric Eastern Coast. Long-range transport studies [16, 18] based in field experiments were completed with the application of dispersion models [35, 36], establishing the ozone transport along stable nocturnal layers from Central Europe and, even, from Central Iberia. Finally, some studies were focused on the meteorological patterns associated to ozone peaks [37, 38].…”

Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: results from the Mt. Waliguan Observatory

“…In the present study, we utilized the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYS-PLIT, version 4.8) developed by the National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory (ARL) (http://ready.arl.noaa.gov/HYSPLIT.php) to calculate three-dimensional backward trajectories. The meteorological input is the National Centers for Environmental Prediction (NCEP) FNL data with a spatial resolution of 191 km × 191 km and a temporal frequency of 6 h, which is widely used to predict the large-scale meteorological conditions and transport (Gangoiti et al, 2006;Lin et al, 2009). Considering the high wind speeds at mountainous sites and relatively short lifetimes of many VOC species, we chose to compute back trajectories for 5 days.…”