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.

High altitude mountaintop observatories provide the opportunity to study aerosol properties in the free troposphere without the added expense and difficulty of making airborne measurements. Over the last several decades the number of mountaintop observatories continuously measuring in-situ aerosol radiative properties has increased significantly from a single station (Mauna Loa, USA) in the 1970's to at least ten observatories actively making these measurements today. By taking this data set as a whole and developing a self-consistent climatology, the combined observatory measurements of free tropospheric aerosol radiative properties have the potential to contribute to aerosol-climate research in a way that far exceeds the contribution from individual observatories. For example, this type of analysis may help constrain chemical transport models, validate satellite measurements, and quantify the influence of smoke and dust episodes on free troposphere aerosol properties. Here we present statistics of means, variability, and trends of aerosol radiative properties, including light scattering, light absorption, light extinction, single scattering albedo, Ångström exponent, hemispheric backscatter fraction and radiative forcing efficiency, from various high altitude measurements. These climatologies utilize data from ten mountaintop observatories in the 20-50ºN latitude band: Mauna Loa, USA; Lulin Mountain, Taiwan; Pyramid, Nepal; Izaña, Spain; Mount Waliguan, China; Beo Moussala, Bulgaria; Mount Bachelor, USA; Monte Cimone, Italy; Jungfraujoch, Switzerland; Whistler Mountain, Canada. Results are also included from two multi-year, in-situ aerosol vertical profiling programs: Southern Great Plains, USA and Bondville, USA. Using this cloud- and boundary layer contamination- screened data set we address the following questions: (1) What are the similarities and differences in the means, variability and trends of free-tropospheric aerosol radiative properties at a wide range of locations? (2) What is the relative importance of aerosol amount and aerosol optical properties for direct radiative forcing calculations? Delene and Ogren (2002) showed that the amount of aerosol was of primary importance while the aerosol optical properties were of secondary importance to direct radiative forcing calculations for the four boundary layer sites they studied. (3) How do these in-situ climatologies of free tropospheric light extinction compare to the satellite-derived climatologies presented by Kent et al., 1998? (4) Do aerosol events (e.g., smoke transport) have a significant influence on climatological values?