Ozone Partial Pressure nbar

Figure 13, The ozone hole. The figure on the left shows the decrease in ihe total ozone column over the Antarctic (I Oil Dobson units corresponds to a layer of ozone I mm thick as standard temperature and pressure at the earth surface). The right-hand diagram shows the altitude dependence of ozone loss between August and October 1987. Measurements by J. Far man and coworkers of the British Antarctic Survey (1985) and by D. Hofmann and coworkers (1989) of the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado.

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at high latitudes in the winter especially over Antarctica, condensation or sublimation of nitric acid (HNO3) and water vapor takes place on particles (Crutzen and Arnold, 1986; Toon et aL, 1986; Dye et aL, 1992) that are always present in the stratosphere and that normally consist of water and sulfuric acid (H2SO4). '["his process effectively removes HNO3 from the gas phase, and with it also the nitrogen oxides (NO and NO2). What then happens is that HQ and CIONO2, the two most abundant inorganic chlorine species - which do not react with ozone or with each other in the gas phase - react in, or on the surface of, the particles to form CI2 and HNOj (Solomon et al., 1986; Molina et al., 1987; Tolbert et aL, 1987):

Then, in late winter or early spring, when sunlight returns after the long polar night, the O2 molecules arc quickly split, producing CI atoms. These start a very efficient cataly tic chain of reactions (Molina and Molina, 1987), w hich results in the rapid transformation of two ozone molecules into three oxygen molecules.

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