Beryllium-7 （^7Be） and lead-210 （^210pb） activities were measured from October 2002 to January 2004 at Waliguan Observatory （WO： 36.287°N, 100.898°E, 3816 m a.s.l （above sea level） in northwest China...Beryllium-7 （^7Be） and lead-210 （^210pb） activities were measured from October 2002 to January 2004 at Waliguan Observatory （WO： 36.287°N, 100.898°E, 3816 m a.s.l （above sea level） in northwest China. ^7Be and ^210pb activities are high with overall averages of 14.74-3.5 mBq m^-3 and 1.8±0.8 mBq m^-3 respectively. For both 7Be and ^210pb, there are significant short-term and seasonal variations with a commonly low value in summer （May-September） and a monthly maximum in April （for ^7Be） and in December （for ^210pb）. The ratio of ^7Be/^210pb showed a broad maximum extending from April to July, coinciding with a seasonal peak in surface ozone （O3）. The seasonal cycles of ^7Be and ^210pb activities were greatly influenced by precipitation and thermal dynamical conditions over the boundary layer, especially for ^210Pb. The vertical mixing process between the boundary layer and the aloft air modulates the variations of ^7Be and ^210pb at WO in summer. It is indicated that air mass had longer residence time and originated from higher altitudes at WO in the spring-summer time and the winter in 2003. During an event with extremely high weeklyaveraged ^7Be concentration （24.8 mBq m^-3） together with high O3 levels and low water mixing ratio, we found that air masses had been convectively transported a long distance to WO from high latitude source regions in central Asia, where significant subsiding motions were observed. In another case with the extreme ^210pb activity of 5.7 mBq m^-3 high CO2 level and specific humidity （in winter）, air masses had come from south China and north Indian regions where 222Rn activities were high. This study, using ^7Be and ^210pb as atmospheric tracers, has revealed that complex interactions of convective mixing from the upper troposphere and long-range transports exist at WO.展开更多
基金the National Science Foundation of China （Grant Nos. 40175032 , 40575013）.
文摘Beryllium-7 （^7Be） and lead-210 （^210pb） activities were measured from October 2002 to January 2004 at Waliguan Observatory （WO： 36.287°N, 100.898°E, 3816 m a.s.l （above sea level） in northwest China. ^7Be and ^210pb activities are high with overall averages of 14.74-3.5 mBq m^-3 and 1.8±0.8 mBq m^-3 respectively. For both 7Be and ^210pb, there are significant short-term and seasonal variations with a commonly low value in summer （May-September） and a monthly maximum in April （for ^7Be） and in December （for ^210pb）. The ratio of ^7Be/^210pb showed a broad maximum extending from April to July, coinciding with a seasonal peak in surface ozone （O3）. The seasonal cycles of ^7Be and ^210pb activities were greatly influenced by precipitation and thermal dynamical conditions over the boundary layer, especially for ^210Pb. The vertical mixing process between the boundary layer and the aloft air modulates the variations of ^7Be and ^210pb at WO in summer. It is indicated that air mass had longer residence time and originated from higher altitudes at WO in the spring-summer time and the winter in 2003. During an event with extremely high weeklyaveraged ^7Be concentration （24.8 mBq m^-3） together with high O3 levels and low water mixing ratio, we found that air masses had been convectively transported a long distance to WO from high latitude source regions in central Asia, where significant subsiding motions were observed. In another case with the extreme ^210pb activity of 5.7 mBq m^-3 high CO2 level and specific humidity （in winter）, air masses had come from south China and north Indian regions where 222Rn activities were high. This study, using ^7Be and ^210pb as atmospheric tracers, has revealed that complex interactions of convective mixing from the upper troposphere and long-range transports exist at WO.
