TRENDS IN PHOTOCHEMICAL SMOG IN THE CAPE PENINSULA AND THE IMPLICATIONS FOR HEALTH

There has been growing public concern over reports of increasing air p ollution in the Cape Peninsula. Attention has been focused on the 'bro wn haze' and on photochemical smog. Because of deficiencies in the mon itoring equipment, information on trends in photochemical smog levels over the past decade is limited. Trends in oxides of nitrogen, one of the main precursors of photochemical smog, and therefore an indicator of the potential for its formation, were examined for the period 1984 - 1993. Meaningful data for determining trends were available from onl y a single site. Increases in mean monthly levels, peak hourly levels and the number of times guidelines were exceeded were demonstrated. Gi ven the dynamics of formation of photochemical smog and the particular role of motor vehicles, it is argued that the trends measured at this site are probably an underestimate of the trends in other parts of th e Cape Town metropolitan area. Some of the precursors of photochemical smog, notably nitrogen dioxide, and some of its components, notably o zone, have been shown to be detrimental to respiratory health at level s close to, or below, current recommended guidelines. A continuing inc rease in these pollutants will therefore result in more respiratory il lness, particularly among susceptible groups. This calls for an upgrad ing of monitoring of air pollution in Cape Town and for appropriate st eps to prevent its further increase.