tailieunhanh - Air Quality Part 6

Tham khảo tài liệu 'air quality part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 118 Air Quality significant quantities in soils are usually not detectable in air thus if found on leaves they are mainly resuspended from soils Vandenhove et al. 2009 . The soil-to-plant transfer factor above is reported for 40K while values for uranium and thorium are much lower 10-4 Uchida et al. 2007 . In higher plants the distribution of the radionuclides is uneven. In tropical forest plants for example the highest 40K concentrations are found in stem and the lowest in root while 137Cs is mostly accumulated in root Somashekarappa et al. 1996 . Beryllium-7 half-life days is produced by cosmic rays in spallation processes with light elements nitrogen oxygen carbon in the upper troposphere and lower stratosphere. Its production depends on the Earth s magnetic field and the variations in its annual mean concentrations are a good indicator of changes in the atmospheric production rate caused by cosmic ray intensity. The 7Be seasonal patterns are correlated to the stratosphere-to-tropo-sphere exchange processes. The 7Be concentration in ground level air in the midlatitudes has the maximum during spring and summer . Ajtic et al. 2008 caused by a seasonal thinning of the tropopause which allows the 7Be rich stratospheric masses to enter the troposphere Gerasopoulos et al. 2003 . Lead-210 half-life years is an effective tracer of continental surface air masses history and often used to identify soil aerosols sources. It mostly originates from the decay of uranium-238 in the Earth s crust but anthropogenic sources uranium ores sintering coal combustion production or use of phosphate fertilizers also contribute to the total 210Pb in air UNCEAR 1988 . Deposition of 210Pb varies with season and geographical position. The 210Pb concentration maxima in fall could be attributed to an enriched emanation of radon. Radon emanation and therefore concentration of 210Pb in air is affected by atmospheric pressure temperature inversions covering vegetation snow and

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