Transport of Tropospheric Ozone over the Bay of Biscay and the Eastern Cantabrian Coast of Spain

Abstract

During the 1989 field campaigns of the European Commission?s Mesometeorological Cycles of Air Pollution in the Iberian Peninsula (MECAPIP) project (1988?91), airborne data were obtained under typical summer synoptic weather conditions, that is, a ridge of the Azores high pressure system extending over the north coast of the Iberian Peninsula combined with a thermal low in the interior of the peninsula. This paper presents a detailed analysis of the flights over the coastal area of Bilbao and a high-resolution simulation of the trajectories of the polluted air masses to determine the mechanisms leading to the type of stratification observed. Over the Bay of Biscay, on the eastern Cantabrian coast, the data showed the presence of two distinct groups of atmospheric strata with high ozone concentrations. The higher layers contained older pollutants, trapped between an inversion at about 1200 m and a near-isothermal layer at about 2000 m, and were moving under persistent north to northeasterly winds. The lowest layers, close to the surface in the Bilbao area, contained recently emitted pollutants. Back trajectories computed by using the 3D wind field simulated by the Regional Atmospheric Modeling System (RAMS) have shown that the source of the pollutants in the upper layers, 36 h before, was within a region near the English Channel.