Long-term measurements of 222Rn in soil gas and at different height levels in Amazon tall tower observatory

Abstract

Emitted from soil as a radioactive noble gas, 222Rn has the potential to be used as a tracer for greenhouse gases. In the atmosphere, it undergoes transport and mixing processes that depend on climatological factors. Therefore, studying factors that influence radon dispersion in hotspot areas can improve our understanding of the driving forces behind atmospheric gas behavior. This study presents data obtained from five years of soil gas measurements at various heights above ground level (18 m, 40 m, and 80 m) below and above the forest canopy in the pristine area of the Amazon Tall Tower Observatory to identify important soil parameters related to radon activity concentration. The results indicate that moisture significantly affects radon activity concentrations during dry and wet periods. The mean 226Ra activity concentration in the soil is 28.3 ± 2.1 Bq/kg. In topsoil, 222Rn varies from 152 to 470 Bq/m3 at ground level, from 1.2 to 10.3 Bq/m3 at 18 m, from 0.37 to 8.6 Bq/m3 at 40 m, and from 1.0 to 5.0 Bq/m3 at 80 m. Daily variations show higher activity concentrations in the early morning, while monthly variations show higher activity concentrations during the dry period.