A comprehensive global dataset of atmospheric 7 Be and 210 Pb measurements : air concentration and depositional flux

7Be and 210Pb air concentration and depositional flux data provide key information on the origins and movements of air masses, as well as deposition processes and residence time of aerosols. 15 After their deposition onto the Earth’s surface, they are utilized for tracing soil redistribution processes on land and particle dynamics and mixing processes in the ocean. Here we present a global dataset of air concentration and depositional flux measurements of atmospheric 7Be and 210Pb made by a large number of researchers and laboratories. Data were collected from published papers between 1955 and early 2020. It includes the annual surface air concentrations data of 7Be from 367 sites and of 210Pb from 270 sites, 20 the annual depositional flux of 7Be from 279 sites, and of 210Pb from 602 sites. When available, appropriate metadata have also been summarized, including geographic location, sampling date, methodology, annual precipitation, and references. The dataset is available at https://doi.org/10.5281/zenodo.4521649 (Zhang et al., 2021). The purpose of this paper is to have the published data available in one place for future researchers’ public consumption in their research and 25 provide an overview of the scope and nature of this dataset holdings.

program was used to digitize the data from graphics, the same was done for geographical location and annual precipitation. In rare cases, only the locality name of the study site was available, the geographical 235 location was digitized by Google Earth. Although the 210 Pb concentration and depositional flux are expected to heavily depend on the source(s) of air mass(es), and not to depend on the latitude, the 10° latitudinal variability of 210 Pb concentration and depositional flux in the Northern and Southern hemisphere is observed ( Fig. 5b and 5d). The

Contribution of dry deposition and effect of precipitation on depositional flux
320 It was reported that dry deposition of 7 Be and 210 Pb generally accounts for less than 10% of the total deposition (Talbot and Andren, 1983;Brown et al., 1989;Todd et al., 1989), however, the fraction of dry deposition of 7 Be and 210 Pb is highly variable (McNeary and Baskaran, 2003;Pham et al., 2013). It is likely that the contribution of dry fallout could increase when annual precipitation decreases (McNeary and Baskaran, 2003). The fraction of dry to total depositional flux of 7 Be and 210 Pb are presented in Fig.   325 6a and 6b. Globally, the fraction of dry to total depositional flux of 7 Be and 210 Pb ranged from 1% to 44% (mean:12±9%, n=29, excluding one extreme site without precipitation) and from 5% to 51% (mean: 21±12%, n=26), respectively (Fig. 6c). The low fraction of dry to total depositional fluxes of 7 Be and 210 Pb suggest that these nuclides are removed from the atmosphere primarily by precipitation (both rain and snowfall). Our results also support previous studies (Baskaran et al., 1993;Benitez-Nelson and 330 Buesseler, 1999) that the fraction of dry deposition is higher for 210 Pb than 7 Be. The fraction of dry fallout of 7 Be and 210 Pb is plotted against annual precipitation in Fig. 6d   As precipitation is the primary mechanism of removal of these nuclides from the atmosphere, the annual 340 depositional fluxes of these nuclides generally depend on the amount and frequency of precipitation. In our dataset, the world's lowest 7 Be depositional flux (only 59 Bq m -2 y -1 , less than 5% of that in the same latitude) was observed in a precipitation area, the Judean Desert (Belmaker et al., 2011). The highest 7 Be (6350 Bq m -2 y -1 ) and 210 Pb (2539 Bq m -2 y -1 ) depositional flux were observed in heavy rainfall areas, Hokitika (Harvey and Matthews, 1989) and Taiwan (Huh and Su, 2004), respectively. Positive 345 correlations between annual depositional flux and precipitation have been observed on a local scale (e.g. Narazaki et al., 2003;Garcia-Orellana et al., 2006;Sanchez-Cabeza et al, 2007;Leppanen et al., 2019).
Here we illustrate the effect of precipitation on annual depositional flux on a global scale (Figs. 7 and 8).

7 Be/ 210 Pb ratios and deposition velocities
Considering that some data come from the same station, we further calculated the ratios of 7 Be to 210 Pb 360 and deposition velocities of aerosols using 7 Be and 210 Pb data, as shown in Figs. 9 and 10.
The variations in the 7 Be/ 210 Pb ratios reflect both vertical and horizontal transport in the atmosphere (Baskaran, 1995;Koch et al., 1996;Arimoto et al., 1999;Lee et al., 2007;Tositti et al., 2014 model (Koch et al., 1996), with a positive south poleward gradient and a little variation in the northern 365 hemisphere. Globally, the 7 Be/ 210 Pb air concentration ratio ranged from 2 to 222, and the 7 Be/ 210 Pb depositional flux ratio ranged from 2 to 229. In 19 sites, 7 Be/ 210 Pb air concentration ratio and depositional flux ratio are available simultaneously, the paired t-test indicates that at 0.05 level the 7 Be/ 210 Pb air concentration ratio and depositional flux ratio are not significantly different. depositional flux (F) at the same site are available, the average total deposition velocities of aerosols that carry these nuclides (Vd) can be calculated by the following Eq. (1): Thus, the Vd obtained from 7 Be and 210 Pb can be used to determine the depositional flux of analog species 380 (Turekian et al., 1983) with a knowledge of the air concentration of these analog species, assuming that the scavenging behavior of analog species is similar to 7 Be and 210 Pb. The Vd for 7 Be ranged from 0. s -1 . The deposition velocity of aerosols collected over a period of 17 months in Detroit, MI, USA varied over two orders of magnitude, from 0.2 to 3.6 (mean: 1.6, n=30) cm s -1 for 7 Be and 0.04 to 3.6 cm s -1

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(mean: 1.1, n=30) cm s -1 (McNeary and Baskaran, 2003). A summary of depositional velocity from 10 different stations are also given in McNeary and Baskaran (2003). Earlier studies suggested that, at continental sites, Vd of 7 Be will be higher than Vd of 210 Pb using the ground level as the reference, which is an artifact of the manner in the calculation (Turekian et al., 1983;Todd et al., 1989;McNeary and Baskaran, 2003). However, later works observed opposite results (

Investigations on global atmospheric dynamics and climate changes
Developing numerical models in which aerosols, chemistry, radiation, and clouds interact with one another and with atmospheric dynamics is important for understanding and predicting global climate 400 changes (Brost et al., 1991). In such atmospheric dynamic models, the major uncertainty is from the parameterization of subgrid-scale processes such as precipitation scavenging, vertical transport, and 1 / mean-life of the isotope, y) indicates notable sediment focusing or additional particle input other than atmospheric fallout (Swarzenski et al., 2006;Lepore et al., 2009;Wang et al., 2020). Thus, the atmospheric depositional flux data are also important for tracing particle dynamics using 7 Be and 210 Pbex.
We believe that the atmospheric depositional flux data presented in our dataset will benefit and facilitate 435 soil or coastal sediment erosion/focusing and particle dynamics studies.
The atmospheric depositional flux (or ocean inventory) data of 7 Be serve as an indispensable parameter for tracing surface ocean process (e.g. subduction, upwelling, and depositional flux of trace metals) (Kadko, 2017;Kadko and Olsen, 1996;Kadko et al., 2015). Due to the low activity of 7 Be in open ocean waters, usually, 400-700 L seawater is needed, which imposes some limitations for sampling, especially 440 for deep layers. This constraint has hampered its application. As mentioned above, 7 Be depositional flux is independent of longitude and is constant over broad latitudinal bands. Thus, the 7 Be depositional flux data in our dataset can be used to estimate 7 Be ocean inventory in the same latitude, which can avoid the collection of the large volume of seawater samples and extend the application of 7 Be in the Open Ocean.

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Our dataset represents an ambitious expansion in comparison to the 7 Be or 210 Pb datasets currently available (Brost et al., 1991;Preiss et al., 1996;Persson et al., 2016). Although the spatial coverage of this dataset is more significant, it is still unevenly distributed. Compared to depositional flux, the coverage of air concentration is large. The air concentration measurement at oceanic sites is adequate, but the depositional flux measurement at oceanic sites is rare. Concerning air concentrations in areas 450 such as Europe, East Asia, eastern Oceania, and the eastern United States are well covered, whereas other areas such as the African continent and Northern Asia are underrepresented. A similar spatial coverage pattern exists for the depositional flux of these nuclides, but the regional gaps are more notable, especially for 7 Be flux data which almost non-existent in Antarctica and African continents. In addition, it needs to be emphasized that the number of sampling sites, in which both concentration and flux of 7 Be and 210 Pb

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were measured simultaneously, are limited. Finally, we acknowledge that the seasonal information is indeed not much discussed for this dataset.
We recommend that future studies should pay more attention to those areas that are currently

Data formats and availability
For clarity and convenience, four separate worksheets, each named as 7 Be or 210 Pb annual air concentration and 7 Be or 210 Pb annual atmospheric flux, are available in one Microsoft Excel ® file,

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although sometimes these data come from the same literature. The dataset can be downloaded from Zenodo (https://doi.org/10.5281/zenodo.4521649, Zhang et al., 2021). It is free for scientific applications, but the free availability does not constitute a license to reproduce or publish it.

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FZ is responsible for most of the writing of this article, along with the assembly of the data and preparation of the figures. QZ and YW assisted FZ in compiling the data. JW, MB, QZ, PJ and JD contributed to the review of the manuscript.

Competing interests
The authors declare that they have no conflict of interest. Tsunogai, S., Kurata, T., Suzuki, T., and Yokota, K.: Seasonal variation of atmospheric 210 Pb and Al in the western North Pacific region, J. Atmos. Chem., 7, 389-407, 1988.