Estimation of the Global 222Rn Flux Density from the Earth's Surface

Abstract

Global 222 in the period of 1979-2007 using an 222 Rn exhalation model based on a porous media diffusion theory. This exhalation model calculated the 222 226 Ra content, soil water saturation, and soil temperature. The -2 s -1 . The annual variation in the -2 s -1 in March to a maximum of 23.6 mBq m -2 s -1 in September. The regional averages for the annual flux density varied from 8.3 mBq m -2 s -1 for the northern part of North America to 33.5 mBq m -2 s -1 for Australia. The latitudinal distribution of zonally averaged flux density was found to be in good agreement with the latitudinal decline at high latitudes in the Northern Hemisphere. The spatial and temporal variations were caused mainly by variations in the soil water content and soil 226 Ra content, but to a lesser extent by the soil simulated atmospheric 222 Rn concentration was substantially lower than that measured at Hachijo Island, implying that the

Inferring <sup>222</sup>Rn soil fluxes from ambient <sup>222</sup>Rn activity and eddy covariance measurements of CO<sub>2</sub>

“…for each wind sector or soil moisture content (if monitored), or use a process model (e.g. Hirao et al, 2010;Karstens et al, 2015a) for extrapolating the flux after calibration with SPOT-EC.…”

“…Recently, several approaches have been applied to quantify 222 Rn surface fluxes: (1) using gamma dose radiation as a proxy for 222 Rn (Szegvary et al, 2007;Manohar et al, 2016) and (2) modelling the production and transport of 222 Rn in soils (Hirao et al, 2010;Karstens et al, 2015a). These efforts have provided new tools for studying the driving mechanisms behind the 222 Rn soil flux on relatively large spatial scales.…”

Simulation of radon-222 with the GEOS-Chem global model: Emissions, seasonality, and convective transport

“…These values are considered much higher than typical 222 Rn emission known for Europe, where Szegvary et al (2009) suggested half of the continent has emissions ranging from 8.33 to 14.6 mBq m -2 s -1 (0.40 to 0.70 atom m -2 20 s -1 ). Hirao et al (2010) also found that, to better match surface observations at Hachijo Island, a volcanic island about 287 kilometers south of Tokyo in the Philippine Sea, the emissions over East Asia would need to be increased by a factor of 1.69.…”

“…Consistently, Zahorowski et al (2005) found Based on three-year winter-time 222 Rn observations at Sado Island, Japan, and associated trajectory analyses, Williams et al (2009) suggested that emission fluxes can be 1.75 times higher in the lower 15 latitude bands over the Asian continent compared to higher latitudes. In an inverse modeling of Asian 222 Rn emissions, Hirao et al (2010) showed an area-weighted average 222 Rn emission of 33.0 mBq m -2 s -1 (~1.57 atom m -2 s -1 ) in Asia with the highest emissions found in central and southeastern Asia. These values are considered much higher than typical 222 Rn emission known for Europe, where Szegvary et al (2009) suggested half of the continent has emissions ranging from 8.33 to 14.6 mBq m -2 s -1 (0.40 to 0.70 atom m -2 20 s -1 ).…”

“…Zhuo et al (2008) compiled radium content information from over a thousand sites in China and constructed a high spatial resolution emission 5 map over the country. Hirao et al (2010) constructed a decade-long global 222 Rn emission record based on additional considerations about surface texture. Due to the availability of extensive measurements of 222 Rn emission fluxes and surface concentrations, Europe has the finest resolution emission inventory of up to 0.083° ×0.083° with variability in regional and temporal emissions (Karstens et al, 2015;López-Coto et al, 2013;Szegvary et al, 2009).…”