Abstract
This work presents the analysis of weekly 7Be activity concentrations in the air measured in Bilbao (northern Spain) by collecting aerosols in filters over a ten years period (2009–2018). 7Be level is in the 0.35–7.3 mBq/m3 range, with a mean of 3.20 ± 1.12 mBq/m3. The trend, cycle, seasonal and monthly variability are evaluated using time series analysis techniques. The results indicate the impact of sunspots (24th solar cycle) on interannual 7Be activity concentrations, and a significant seasonal and monthly variation, with maximum concentrations occurring in spring-summer and minimum in the winter. The correlation of different 7Be ranges with local meteorological parameters, such as precipitation, temperature, relative humidity, and pressure, is also addressed, with precipitation having the greatest impact on 7Be activity values. The analysis of synoptic airflows, by calculating the back-trajectory clusters, and local winds at surface level reveals the important influence of the arrival of slow northwest Atlantic flows and the development of breezes on reaching high 7Be activity concentrations in this area.
Highlights
Beryllium-7 (7Be), a cosmogenic isotope with a half-life of 53.6 days, is one of the natural radionuclides most widely measured around the world
The observed chi-square test statistic is greater than the critical value, which allows us to conclude that 7 Be concentrations follow a normal distribution, similar to the one obtained in Todorovica [29] and Dueñas [30], but different, for instance, to the one presented in Lozano [17]
Our study looked into the description of 7 Be activity concentrations measured in the Bilbao sampling station from 2009 to 2018 and its link with meteorological parameters
Summary
Beryllium-7 (7Be), a cosmogenic isotope with a half-life of 53.6 days, is one of the natural radionuclides most widely measured around the world. Due to the nature of its production, as a result of the spallation of nitrogen and oxygen nuclei by components of an atmospheric cascade induced by the galactic cosmic rays [8], 7 Be concentrations increases with height (2/3 of the total amount is produced in the stratosphere) [9]. It has a maximum production at 15 km altitude, where cosmic rays are strongly attenuated by the atmosphere
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