Meteorological Factors Controlling 7Be Activity Concentrations in the Atmospheric Surface Layer in Northern Spain

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.

Five Years (2014–2018) of Beta Activity Concentration and the Impact of Synoptic and Local Meteorological Conditions in Bilbao (Northern Spain)

“…The minimum value (P5) increases from 107 µBq/m 3 to 224 µBq/m 3 , while the maximum value (P95) ranges from 803 µBq/m 3 to 1315 µBq/m 3 . The occurrence of the maximum in autumn is not in line with previous works analyzing beta activity concentrations conducted in the Iberian Peninsula [16][17][18], which showed that the maximum average values are reached in the summer and that the minimum values are obtained in the winter. On the contrary, similar behaviour has been found in other analyses, such as in Milan [27] and New York [28].…”

“…On the same roof where the low air sampler was located, there was also a high flow sampler. From 2001 to 2018, during two periods of time (2001-2008 and 2009-2018), the 7 Be concentration had been analysed [14,15,17,18].…”

“…These files include vertical wind component information, which makes it possible to calculate three-dimensional kinematic air trajectories. Following the methodology used in previous studies conducted in the same area [17], air trajectories with a duration of 96 h, in time steps of 1 h, and at an ending altitude of 100 m above ground level were calculated. Four backward air trajectories were calculated for each sampling period considered in the present study (one every six hours).…”

Meteorological Approach in the Identification of Local and Remote Potential Sources of Radon: An Example in Northern Iberian Peninsula

“…During the studied period (2017-2018), temperature averages between 11 • C in winter and 21 • C in summer, while annual precipitation averages over 830 mm, with a yearly average of 142 days with at least 1 mm. Previous analysis [21] has demonstrated that this area is typically affected by air masses from the northwest, west, north, northeast, and south, which are combined in spring and summer with the development of mesoscale circulations in surface levels, i.e., sea-land breezes.…”

Analysis of Factors Contributing to the Increase in 7Be Activity Concentrations in the Atmosphere

“…Atmospheric 7 Be near ground level generally seems to be originated from the upper troposphere, due to its relatively short physical half-life (53.3 days) and long removal time (1–2 years) in the stratosphere [ 6 ]. The following factors are known to produce the (seasonal) fluctuations in 7 Be activity concentration levels at ground level [ 7 , 8 , 9 ]: cosmic-ray intensity [ 10 , 11 ], the exchange of atmosphere between the troposphere and stratosphere [ 12 , 13 ], the north–south or east–west mixing of atmosphere [ 14 ], and the frequency of precipitation [ 15 , 16 ].…”