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

[摘要] Two ozone episodes (occurring in June 2001 and June 2003)in the air quality monitoring network of the Basque Country (BC) areanalyzed. The population information threshold was exceeded in many stations(urban, urban-background and rural). During this type of episodes, forced bya blocking anticyclone over the British Isles, ozone backgroundconcentrations over the area increase after the import of pollution fromboth, the continental Europe and the western Mediterranean areas (Gangoitiet al., 2002). For the present analysis, emphasis is made in the search fortransport mechanisms, pathways and area sources contributing to the build-upof the episodes. Contributions from a selection of 17 urban and industrialconglomerates in the western European Atlantic (WEA) and the westernMediterranean (WM) are shown after the results of a coupled RAMS-HYPACTmodelling system. Meteorological simulations are tested against both thehigh-resolution wind data recorded at the BC coastal area by a boundarylayer wind-profiler radar (Alonso et al., 1998) and the wind soundingsreported by the National Centres of Meteorology at a selection of Europeanand north-African sites. Results show that during the accumulation phase ofthe episodes, background ozone concentrations increase in the wholeterritory as a consequence of transport from the Atlantic coast of Franceand 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 increasein the ozone concentrations. Direct day and night transport within thenorth-easterly winds over the sea from the WEA source region, and night-timetransport within the residual layer over continental areas (southern France,the Ebro Valley, and central Iberia) modulate the import sequence ofpollutants and the local increase of ozone concentrations. The alternativedirect use of low resolution meteorological data for the estimation ofback-trajectories shows a more simple transport scheme with no contributionsneither from the Western Mediterranean nor from the Madrid area.

[学科分类] 大气科学