Analyses and comparisons of 7Be, 210Pb and activity ratio 7Be/210Pb with ozone observations at two GAW stations from high mountains

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 changes occurring at high altitude because they can provide diagnostic indicators of horizontal and vertical exchange processes of transport. The increase (decrease) of 7Be with decrease (increase) of 210Pb associated with high (low) value of 7Be/210Pb generally indicates the mechanisms associated with vertical (for being favorable to the horizontal) transport occurring. Distinct transport processes and background conditions for two Global Atmosphere Watch (GAW) stations, Mt. Waliguan (36.29o N, 100.90o E, 3816 m a.s.l.) and Mt. Cimone (44.18o N,10.7o E, 2165 m a.s.l.) located in the high mountains of China and in Italy, respectively, are presented. We have performed the frequency distribution analyses and various comparisons of 7Be with 210Pb, the surface ozone with 7Be and 7Be/210Pb. Our study reveals that the maximum ozone levels occur in the summer and minimum levels occur in the winter at these two high mountain stations. Our analyses show 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 Mt. Waliguan station. The ozone summer peak at the Mt. 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 scale. Frequency distribution analyses of the concentrations of 7Be, 210Pb and the values of 7Be/210Pb can be well represented by the log-normal 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 log-normal distributions of 7Be and 210Pb, with the noteworthy difference in altitude of these two stations, are significantly different. The measurements of 7Be and 210Pb accompanied with the analyses using 7Be/210Pb activity ratio, can enhance our understanding of the transport processes in the atmosphere