Transport and dispersion of atmospheric sulphur dioxide from an industrial coastal area during a sea-breeze event

Abstract. Experimental and modelling results of the dynamics of a sea-breeze event and its effects on the three-dimensional (3-D) redistribution of the gaseous SO₂ are presented within the framework of a particularly flat and industrialized coastal area of the North Sea. The measurements were carried out at ground level with the stations of the local air quality monitoring agency and with two optical remote sensing instruments. The remote sensing setup consisted of a lidar and a sodar whose measurements allowed us to determine the layers of the lower troposphere during a sea-breeze event up to 1400 m height. The experimental results and measurements of industrial SO₂ in the atmosphere are compared to the numerical simulations of the 3-D atmospheric non-hydrostatic chemistry model Meso-NH-C. The transport and the dispersion of gaseous SO₂ are studied above the neighbouring industrial and urban areas. We show how the evolution and the redistribution of the SO₂ concentrations at ground level are related to the structure and the dynamics of the sea breeze. The gaseous SO₂ is brought back inland as soon as the sea breeze commences, mixed inner the thermal internal boundary layer and transported inland by the gravity current up to the sea-breeze front, where gases and particles are uplifted. The elevation of the polluted air masses by the sea-breeze system favours the nucleation of the emitted compounds due to the increase of the relative humidity in the uplifted layer. We show how the dynamical conditions during and after the sea breeze lead to storage of SO₂ near and above the emitting industrial coastal areas, and favour the formation of acidic aerosol particles.