Simultaneous measurements of 7Be and 210Pb and the analyses of activity ratio, i.e., 7Be/210Pb, offer another useful analytical tool for improving our understanding of ozone variability occurring at high altitude because they can provide diagnostic indicators of horizontal and vertical transport processes. Generally, the increase (decrease) of 7Be with decrease (increase) of 210Pb in association with high (low) values of 7Be/210Pb indicates the mechanisms associated with vertical (for being favorable to the horizontal) transport processes. For the purpose of demonstrating these mechanisms for ozone transport, we have presented the distinct transport processes of ozone and background conditions for two Global Atmosphere Watch (GAW) stations: Mount Cimone station (44.18°N, 10.7°E, 2165 m asl) and Mount Waliguan station (36.29°N, 100.90°E, 3816 m asl), located high in the mountains of Italy and China, respectively. We have performed the frequency distribution analyses and various comparisons of variations of 7Be with 210Pb and variations of 7Be, 210Pb, and 7Be/210Pb with surface ozone. The maximum ozone levels occur in the summer, and minimum levels occur in the winter at these two high mountain stations. Our analyses suggest that the processes of the stratospheric intrusions/upper tropospheric transport combined with the long‐range transport from polluted areas over eastern central China are the mechanisms that cause the ozone summer peak at the Mount Waliguan station. The ozone summer peak at the Mount Cimone station is mainly the result of photochemical production in the lower atmosphere associated with the transport of polluted air masses on regional and continental scales. Frequency distributions of 7Be, 210Pb, 7Be/210Pb, and surface ozone can be well represented by the lognormal distributions. Strikingly, we have found that the similarities of bimodal distributions for 7Be/210Pb at these two stations are clearly exhibited except for the magnitude, although the lognormal distributions of 7Be and 210Pb, with the noteworthy difference in altitude of these two stations, are significantly different. The measurements of 7Be and 210Pb combined with the analyses using 7Be/210Pb activity ratio can enhance our understanding of the transport processes in the atmosphere.

[1] Previous global models generally simulated high concentrations of 210 Pb in the surface air over China. Measured data of 210 Pb are needed in order to examine the accuracy and performance of the models. We collected the first-ever set of surface air radionuclide measurements of 210 Pb and 7 Be at Guiyang (26.57°N, 106.72°E, 1080 m above sea level) on the east of the Himalayas in Guizhou Province and at Mt. Waliguan (36.29°N, 100.90°E, 3816 m above sea level), a Global Atmosphere Watch station for the World Meteorological Organization, on the Qinghai-Tibetan plateau extending from the Himalayas in Qinghai Province, China. These measurements were carefully analyzed for data assurance and quality control and were used for validating models. The patterns for the variations in both measured 210 Pb and 7 Be at the Guiyang site have been shown to be consistent. In this case the increase of 7 Be concentration was the result of the weak subsidence of air developed at the periphery of the high-pressure system. Because of the weak subsidence the boundary layer turbulence could mix the upward transport of 210 Pb, thus increasing 210 Pb concentration. The ratio of 7 Be/ 210 Pb indicated a seasonal variability with rough monthly oscillation. The ratio peaks were in spring and summer when the convective activities were significant. The 210 Pb levels measured at Mt. Waliguan, located at the peak of the mountain, could be attributed to the long-range transport of 222 Rn that decays to 210 Pb, whereas the 7 Be concentration varied directly with the local airflow passing over the site. We found that it was not appropriate to use the ratio of 7 Be/ 210 Pb for analysis of vertical transport exchange processes at the high-altitude Mt. Waliguan site because of the long-range transport of 210 Pb that occurred at the site.

We simulated the global transport of dust emitted from all major dust source regions on earth by using a global three-dimensional chemical transport model for the year 2000. A modified dust emission flux scheme and an advanced nonlocal diffusion scheme for accurately determining the atmospheric eddy diffusivity in the atmospheric boundary layer were implemented to improve the chemical transport model. We specifically examined and analyzed dust storms that occurred in China and northern Africa. Four scenarios representing the global transport of dust from dust storms originating in the Loess region and the Gobi, Takla Makan, and Sahara deserts, respectively, were simulated. The results of each scenario were then compared with those resulting from all major dust source regions on earth, to identify which deserts have a major impact on dust transport and its deposition in Japan. The dust from the Sahara desert, most from the western part that was found in this study, reached Japan in 9-10 days, while Gobi and Loess region dust took 2 to 3 days, and 4 days for Takla Makan dust. The model-calculated monthly total deposition of dust mass from all major dust source regions was compared with comprehensive measurements of total deposition collected at sampling stations distributed over Japan, and good agreement was generally found. From these analyses, it was also indicated that dust emitted from other deserts, including the Turkestan, Iranian, and Arabian, could have a significant impact on dust deposition on Japan.

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A B S T R A C T Samples of surface air and rain water were collected at the Mt. Guanfeng site located at Guiyang, China. The monthly mean 210 Pb concentrations in surface air exhibited a U-pattern with high values appearing in winter and low values in summer and early autumn. The annual mean of 210 Pb concentrations in surface air was estimated to be 2.7 ± 0.6 mBq m −3 , which was at least four times higher than the annual mean reported from a large number of monitoring stations located throughout the world. The amounts of enriched Uranium in soil at the region could significantly contribute a great deal of release of 222 Rn that decay to 210 Pb which gets attached to the atmospheric aerosols. The site was under the influence of a monsoon climate. The distribution of monthly mean of 210 Pb concentrations in surface air correlates well with the reciprocal of monthly average of observed air temperature and rainfall. The partition coefficients of 210 Pb between rain water-surface air in the winter and spring were larger than those in the summer and autumn. The type and duration of rain depending on season played key roles for the changes of partition coefficients, although the rain amount is important.