Ozone concentrations seasonal fluctuations

Among the first BAS discoveries made at Halley Bay was that ozone concentrations above the South Pole fluctuated on a regular basis annually, with concentrations in late spring about 35 percent higher than in winter. "Spring," in this case, refers to austral, or Southern Hemisphere, spring, beginning after about September 15. Further studies conducted over the next two decades consistently confirmed this seasonal variation. 

When the values for ozone from the above-mentioned studies are averaged, the ozone concentration is smaller than 1 p.p.m. below 33,000 feet, reaches a peak of 6 p.p.m. at 80,000 feet, and falls below 1 p.p.m. again above 114,000 feet. Both the location of the peak and the concentration are subject to considerable fluctuation, so that much greater peak concentration may occur at various altitudes depending on latitude, season, and weather conditions. 

In parallel with their own research programs, the manufacturers, through the FPP also jointly fimded research to study the atmospheric chemistry of CFCs in order to assess the extent of any risk they might pose. Independent research workers of imiversities and research institutes worldwide were contracted to measure the rates of reactions, which were essential input data for the complex computer models needed to predict the rate of ozone depletion. This value could not be measured directly in the 1970s because the large daily and seasonal fluctuations in stratospheric ozone concentrations swamped the modest depletion expected from CFCs. 

Within three months of his arrival at Irvine, Molina and Rowland had developed the rudiments of their CFC-ozone depletion theory. Both became aware that Crutzen s earlier work on the influence of nitrogen oxides on ozone levels provided a model for how chlorine atoms could influence the concentration of ozone as well. By 1985, Molina, working at the Jet Propulsion Laboratory in California, was able to show that the chlorine activation reactions took place effectively in the presence of ice crystals in the polar stratosphere and, thus, account for the seasonal fluctuation of the ozone discovered earlier by Joseph Farman and his coworkers. Molina has stated that he chose the initial research project with Rowland simply out of scientific curiosity, never dreaming of the impact then-work would have on the world s environment. You may read about their exploits, and those of other Nobel laureates, at http //www.nobel.se/ chemistry/laureates/. 

Why are there seasonal fluctuations in ozone concentration above the South Pole ... 

It was pointed out earlier that the natural equilibrium condition for the production and dissociation of ozone resulted in an ozone maximum at some intermediate level in the upper atmosphere. From measurements at different times and by different observers (6, 12, 16, 32, 33, 37, 39, 4I, 4, this maximum has been found to vary in height, thickness, and in general structure, with short and long period fluctuations possibly associated with weather conditions and seasonal variations. On occasion double maxima may appear (41)- Little is yet known, however, about specific relationships between the ozone changes and meteorological conditions except in the instance of seasonal variations (6, 8, 10, 15, 26, 30, 4 ) and certain large air mass movements (9, 56, 59). There is a great need for continuous observations of both the total and the vertical distribution of ozone in order to establish possible relationships between ozone distribution and concentration and solar variation, atmospheric circulation, and weather. 

Diurnal and seasonal variations in solar intensity are, of course, of utmost importance to ecosystems. In the extreme polar regions there is no direct solar radiation at all for more than four months of the year, whereas near the equator the overall intensity of sunlight fluctuates less than 10% annually. The spectral energy distribution also varies with the season. For example, in July in the middle latitudes (ca. 40 ), the fraction of shorter-wave UV (290-315 nm) in the total solar radiation is more than three times higher than it is in December, due to the shorter path these easily scattered wavelengths have to traverse through the atmosphere. For similar reasons, shortwave UV is more intense at high elevations, particularly in the tropics where stratospheric ozone is less concentrated (Caldwell et al., 1980). 

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