7Be atmospheric concentration at mid latitudes (40°N) during a year of solar minimum

Abstract

In this paper we present the variation of 7Be concentration in the surface air of Thessaloniki, Greece (40°62′N, 22°95′E) over the year 2009, a year of a deep solar minimum, and, as a consequence, a year of maximum concentration of 7Be in surface air. The mean annual activity concentration of 7Be for the year 2009 was 6.0 mBq m−3. The relative variability of 7Be surface concentration related to the solar cycle was calculated to be deviated by about 20% from maximum to mean. A positive correlation (R = 0.97) was revealed between the activity of 7Be and the temperature T (°C), confirming that the increased rate of vertical transport within the troposphere, especially during warmer months, that make descend air masses enriched in 7Be down to the surface layer. The anticorrelation (R = –0.65) with RH% is due to intense condensation during high relative humidity conditions, which results in increased aerosol particle sizes and as a consequence in higher scavenging rate of aerosols and lower concentration of 7Be in the atmosphere. The influence of precipitation on the 7Be atmospheric concentration variability was approximately 10%, with greater the influence of rainfall events of low precipitation rate e.g. drizzling.