Environment Geochemistry Character Of ～7Be And ～(210)Pb In Surface Air At Central Guizhou, China

Since the radionuclides ¹³⁷Cs background concentration decreased with time elapsed, two kinds of the nature radionuclides: ⁷Be and ²¹⁰Pb, as two important tracers, have been used widely in atmospheric study. Their source regions make them particularly suitable for the study of atmospheric transport processes. In order to study the Background of the YunGui altiplano and examine the accuracy and performance of the Global Models, EML and State Key Laboratory of Environmental Geochemistry have established a observation station at the Mt. GuanFeng area to obtain the measurements of ⁷Be and ²¹⁰Pb. Two years observation have got more than 100 filters, and there is good agreement between EML and State Key Laboratory of Environmental Geochemistry measured data.This article studied these measured data with precipitation and temperature data about Mt. Guanfeng. The main conclusions have been summarized as follows:1. The annual U-pattern distribution of ²¹⁰Pb high concentrations in surface air at Mt. Guanfeng has been observed. This U-pattern distribution is the representative character of other stations of EML, and it reflect a global distribution of ²¹⁰Pb high concentrations in surface air. One possible factors that affects the source of air ²¹⁰Pb concentrations is high release of ²²²Rn from the U-Ra series in soil-rock system. The recommended geochemical background values of uranium in exogenous sediments of Guizhou are 3.31 ×106. Another possible factor affecting the high ²¹⁰Pb concentrations is dissolution and erosion of carbonate rocks. The impact of exploitation, processing and utilization of coal and phosphorous resources is another factor that affects the high ²¹⁰Pb concentrations in the surface air.2. Meteorologic factors such as precipitations and temperature are main reasons affecting annual U-pattern distribution of ²¹⁰Pb high concentrations. At Mt. Guanfeng area the average monthly ²¹⁰Pb concentrations in the surface air show a good negative power-function relationship with increasing precipitation. They also show a good negative linear-function grouping relationship with the rise of air temperature in month scale, reflects a relatively low release of ²²²Rn from soils in relatively high temperature months and a relatively high release of ²²²Rn from soils in relatively low temperature months respectively. In summary, there are several factors that control the annual U-pattern distribution of ²¹⁰Pb high concentrations in surface air at Mt.Guanfeng and this characters reflects a balance of inland features, low diffusion capability, territorial high release of22 Rn from the U-Ra series in soil-rock system, continent air mass and oceanic air mass, precipitation and temperature.3. A negative correlation is expected between the atmospheric 7Be concentrations and sunspots by some articles, but, 7Be concentrations in the surface air at Mt. Guangfeng is not like this. Due to too short time of observation, detailed discussing on the relationship between sunspots and 7Be concentrations in the surface air at Mt. Guanfeng has not enough conditions.4. Precipitation scavenging and changing of the air pressure around precipitation are main factors that affect 7Be concentrations in surface air of Mt. Guanfeng. The sampling station is situated on the side of Mt. Guanfeng, Guiyang City, China(26° 34' N), and about 1080 meters above sea level. But the 7Be concentrations in surface air show a lack of high altitude and low-attitude character, possible factors affecting this phenomena are territorial high precipitation and other unaware reasons. In fact, precipitation is the main factor that influence 7Be concentrations in surface air, a significant negative correlation between precipitation and 7Be concentrations in filters when the precipitation is above 0.2cm during the sampling time.5. Temperature is another factors that influence 7Be concentrations in the surface air at Mt. Guangfeng. The highest observed 7Be values during summer period were correlated with the elevation of tropopause during the warm summer months and the vertical removal of air masses within the troposphere, which are both stronger during that period. But the influence of temperature is concealed or weakened by high precipitation especially in rainy summer period. Even so, the highest 7Be concentrations in the surface air appears in warm summer months.6. Weekly measurement of 7Be and 210Pb concentrations in the surface air at Mt. Guanfeng show a significant positive correlation, but in month scale, this correlation between 7Be and 210Pb is restricted in the period of Spring to October because of abundant of the precipitation in these months. The result indicate the precipitation is the main factors which control the changing of 7Be and 210Pb concentration in the surface air, and the different size of influencing on two nature radionuclides lead to different annual pattern distribution.7. Monthly and weekly 7Be/210Pb all show a strong seasonal trend with the highest values being observed in the summer and the lowest in the winter period. In summer period, intense convection follow the high temperature and aboundant of Precipitation brings high layer air mass which contains high 7Be concentration result in a high 7Be/210Pb. In contrast, in winter period, fewer convection between high layer and surface air lead to a low 7Be/210Pb comparatively.8. The same seasonal trend of 7Be/210Pb with the highest values being observed in the summer and the lowest in the winter period has been observed at most of EML global stations, so it is obvious that temperature is the main factor to control the changing of 7Be/210Pb value and precipitation is the minor factors.9. Mt. Guanfeng locate the center of Guiyang City, Guizhou Pro., and its 7Be and 210Pb concentrations in the surface air represent central Guizhou. Although precipitation is the main factor of influencing 7Be and 210Pb concentrations in the surface air, it is temperature which control the varieties and the seasonal trends of 7Be/210Pb. hi the sight of vertical transport, relatively high 7Be/210Pb value indicate subsidence of airflow from upper altitudes and vertical air movement or horizontal transport from mid-latitude to high latitude. A low 7Be/210Pb value may reflect weak convection in the troposphere or horizontal transport from high latitude to mid-latitude.