Observational evidence for chemical ozone depletion over the Arctic in winter 1991-92

Long-term depletion of ozone has been observed since the early 1980s in the Antarctic polar vortex, and morerecently at midlatitudes in both hemispheres, with most of the ozone loss occurring in the lower stratosphere.Insufficient measurements of ozone exist, however, to determine decadal trends in ozone concentration in the Arcticwinter. Several studies of ozone concentrations in the Arctic vortex have inferred that chemical ozone loss hasoccurred; but because natural variations in ozone concentration at any given location can be large, deducinglong-term trends from time series is fraught with difficulties. The approaches used previously have often been indirect,typically relying on relationships between ozone and long-lived tracers. Most recently Manney et al. used such anapproach, based on satellite measurements, to conclude that the observed ozone decrease of about 20% in the lowerstratosphere in February and March 1993 was caused by chemical, rather than dynamical, processes. Here we report theresults of a new approach to calculate chemical ozone destruction rates that allows us to compare ozone concentrationsin specific air parcels at different times, thus avoiding the need to make assumptions about ozone/tracer ratios. For theArctic vortex of the 1991-92 winter we find that, at 20 km altitude, chemical ozone loss occurred only between earlyJanuary and mid February and that the loss is proportional to the exposure to sunlight. The timing and magnitude arebroadly consistent with existing understanding of photochemical ozone-depletion processes

Carotenoids as a Source of Antioxidants in the Diet

Capítulo del libro Caroteids in Nature, que corresponde al volumen 79 de la serie Subcellular BiochemistryCarotenoids, widely distributed fat-soluble pigments, are responsible for the attractive colorations of several fruits and vegetables commonly present in our daily diet. They are particularly abundant in yellow-orange fruits (carrots, tomatoes, pumpkins, peppers, among others) and, although masked by chlorophylls, in dark green leafy vegetables. Several health benefits have been attributed to carotenoids or to foods rich in these pigments, by means of different mechanisms-of-action, including the role as provitamin A of almost 50 different carotenoids and the antioxidant activity that protects cells and tissues from damage of free radicals and singlet oxygen, providing enhancement of the immune function, protection from sunburn reactions and delaying the onset of certain types of cancer. Common food sources and the efficiency of the absorption of carotenoids, analytical approaches used for measurement of their antioxidant effect and an overview of some epidemiological studies that have been performed to assess the beneficial impact of carotenoids in human health are outlined in this chapter.Peer reviewe