Hemispheric background

Keywords Hemispheric background, Long-term trends, NOx and VOCs, Ozone, Photochemical ozone formation, Regional pollution controls... 

Currently, there is little SCP and IAS data for the southern hemisphere. Cameron et al. (1993) showed a SCP profile for Lake Nicholls in Tasmania which had a surface concentration just above the level suggested as a northern hemispherical background and an improbably long historical record. Chenhall et al. (1994 1995) presented ash profiles for Lake Illawarra in New South Wales, Australia. Here, the ash, extracted by flotation of... 

Fig. 3. Ideal photon detector sensitivity as a function of cutoff wavelength. Lower background flux generates less photon-induced noise giving higher sensitivity. The sensitivity limit for the condition of 300 K background temperature and hemispherical (27T) field of view is shown.

Am levels reflect resuspension of dust contamination at the WIPP site and not background 241Am levels. Present background levels result from past atmospheric nuclear testing and would be fairly uniform throughout the northern hemisphere. 

Starting with the atmospheric thermonuclear tests, tritium concentration in the Northern Hemisphere has increased considerably above the natural background of approximately 10 pCi/liter of water (5). Since the cessation of these tests, environmental tritium concentrations have decreased gradually. Tritium is, however, produced in every nuclear reactor to some extent as a product of fission (1) or the activation of deuterium. In particular, reactors with heavy water as the moderator or cooling agent produce a large amount of tritium. Inasmuch as no... 

The dose to tissue from HTO is low, because the energy of decay is low and the distribution uniform. In the 1960s, the average dose to man in the northern hemisphere from tritium reached a peak of 2 /uGy a-1, about 0.2% of natural background radiation. 

NO refers to the sum of two of the most reactive nitrogen species NO and NO2. NOx plays a critical role in determining levels of ozone. Over the last 100 years it is believed that tropospheric background levels of ozone in the Northern hemisphere have increased by approximately a factor of two and that this increase has been strongly influenced by increased levels of NO [9]. 

This delicious fruit started to become available in the northern hemisphere during the past 20 years. Its sweet, creamy, fmity taste is reminiscent of fresh cream with strawberries, pineapple and a floral aromatic exotic background in the direction of ylang-ylang, a flower of the same annona family. 

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