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Abstract. Swansea is the wettest city in the UK and has an NO^sub 2^ problem due to traffic. It benefits from an advanced air quality monitoring system. In a coastal area like Swansea, the difference in heating can have a large impact on the weather by the formation of the sea and land breezes. These, coupled with the presence of a windier climate in general, impact upon the dispersion of pollution in the city. Nevertheless, mountains are associated with up and down wind (katabatic airflow), causing air containing pollutants to spread horizontally, reducing the potential for dispersion. The aim of this research is to investigate sea and land breezes of the city of Swansea in relation to topography and in conjunction with urban air quality, together with pollutant exceedences associated with specific weather conditions. Such a phenomenon clearly occurred on 1st and 2nd June 2008 during a summer of otherwise rare sea breezes occurrence. High concentrations of NO^sub 2^, O^sub 3^ and PM^sub 10^ were recorded during the middle of the night between 23:00 hours on 1st June and 01:00 hours on 2nd June, when the sea breeze changed into a katabatic wind, returning Swansea's pollutants to the city under these specific meteorological conditions.
Keywords: Air pollution, Sea breeze, Swansea, Topography.
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Introduction
Sea breezes are important factors affecting pollution, particularly on the local scale. They occur due to differential heating of the air over a region where a large body of water and land meet (Simpson, 1994). They are a phenomenon mostly associated with summer because they are driven by the inland convection currents caused as the land heats the air. The resultant thermal low draws in breezes from the sea, and these have important effects on pollution. During the night-time, sea breezes can reverse and return as a land breeze, together with pollutants collected during the day. Katabatic winds are a function of complex terrain and represent downslope flows of dense cold air. In coastal areas katabatic flows may reinforce night-time land breezes (Kambezidis et al., 1998 and Simpson, 1994).
Sea breezes have potential consequences for the local air pollution of cities on the coast as they tend to complicate and even override prevailing wind patterns, and...