Ship-borne ozone measurements, performed by researchers of the Max Planck Institute for Chemistry and the German Weather Service over the Atlantic Ocean during the period 1977-2002, show that the ozone trends in the northern mid-latitudes are small. In contrast, remarkably large ozone trends occur at low latitudes and in the Southern Hemisphere, implying that the ozone smog problem has expanded far beyond the areas traditionally affected by photochemical air pollution in Europe and the USA (Science Express, 13 May, 2004).
Ozone smog was first discovered in the Los Angeles basin in the 1940s, an area where traffic emissions of nitrogen oxides (NO and NO2) efficiently promote photochemical air pollution. The nitrogen oxides, released from the combustion of fossil fuels and also by biomass burning, act as catalysts of ozone formation. In turn, this reduces air quality and impairs human health, agricultural crops and natural ecosystems. Furthermore, ozone is a greenhouse gas, so that its increasing concentration in the troposphere contributes to climate change. In the post-war industrialization in the 1960s and 1970s, ozone increased rapidly in Europe and the USA. In addition to Los Angeles, especially the eastern USA and southern Europe suffer from high ozone concentrations in summer, so that air quality standards are often violated. Nevertheless, the ozone increases have been moderated after 1980 by the introduction of catalytic converters in car exhausts and the mitigation of industrial air pollution.
The article in Science is based on ozone measurements by the Max Planck Institute for Chemistry (Mainz) and the German Weather Service (Hohenpeißenberg and former Meteorological Observatory Hamburg), taken on ships sailing the Atlantic Ocean since 1977. The results confirm that in middle latitudes in the northern hemisphere the ozone concentrations are quite high, although the increases since about 1980 have not been very large. Remarkably and unexpectedly, however, in the subtropics, the tropics and the southern hemisphere, ozone increases since 1980 have been much larger. In some regions the ozone levels have even doubled in two decades. The area where the high ozone concentrations have been measured is mostly downwind of Africa, and the researchers have calculated that biomass burning and especially increasing energy use on this continent have contributed substantially to emissions of nitrogen oxides, thus catalyzing ozone formation. The implication is that increasing energy use worldwide causes large-scale ozone increases, thus reducing global air quality.
Jos Lelieveld, John van Aardenne, Horst Fischer, Marian de Reus, Jonathan Williams and Peter Winkler Increasing ozone over the Atlantic Ocean Science Express, 13 May 2004
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