Radon-222 in boundary layer and free tropospheric continental outflow events at three ACE-Asia sites

Abstract

A 1‐year record of hourly atmospheric radon‐222 concentration observations at three ACE‐Asia network sites—Hok Tsui (Hong Kong), Gosan (Jeju Island) and Mauna Loa Observatory (Hawaii)—is presented and discussed. The observations include the spring 2001 ACE‐Asia intensive operation period. Site locations were chosen for the experimental characterization of both boundary layer (Hok Tsui, Gosan) and free tropospheric (Mauna Loa) continental outflow to the Pacific. A significant seasonal variability in background radon concentration is quantified at each site with the ratios of winter maximum to summer minimum background of 96, 15 and 3 for Hok Tsui, Gosan and Mauna Loa, respectively. Only during summer were background radon concentrations directly comparable with unperturbed marine values (∼20 mBq m−3). The variability in radon signal was characterized at each site on diurnal to seasonal timescales. The seasonal variability in fetch regions for air masses experiencing the greatest and smallest terrestrial influence was characterized using 10‐day back trajectories of air masses corresponding to radon concentrations higher (lower) than the 90th (10th) percentile value. The trajectory analyses for Hok Tsui and Gosan, as well as a direct analysis of the experimental results, further supports the previously postulated existence of a strong spatial heterogeneity in the radon source strength in East Asia. Back trajectories of free tropospheric air masses reaching Mauna Loa indicated source regions deep within the Asian continent primarily between 20 and 40°N. This fetch region is different from that influencing the Hok Tsui and Gosan sites. The radon concentration of air masses reaching Mauna Loa was shown to vary seasonally as well as with latitude of the predominant fetch region. Possible mechanisms of this phenomenon have been identified and include (a) seasonal variation in the radon source, (b) seasonal variation in the strength, frequency and/or efficiency of mechanisms that lift boundary layer air to the mid troposphere and (c) seasonal variation in the latitudinal axis of convection.

Inverse modeling of Asian 222Rn flux using surface air 222Rn concentration

“…Information on 222 Rn source distribution is considered useful for identifying areas with a high risk of 222 Rn exposure. On the other hand, atmospheric 222 Rn concentrations have been observed as an effective tracer for terrestrial air mass movements and atmospheric mixing (Iida et al, 1996;Wang et al, 2003;Zahorowski et al, 2004Zahorowski et al, , 2005Moriizumi et al, 2008;Ohkura et al, 2009). Its characteristics of chemical inertness and the convenient half-life of 3.82 d have made 222 Rn a useful tool for the evaluation of transport and mixing schemes in chemical transport models (Jacob et al, 1997;Jacob and Prather, 1999;Dentener et al, 1999;Taguchi et al, 2002;Uno et al, 2003;Sakashita et al, 2004;Hirao et al, 2008b).…”

Continuous Observation of Atmospheric222Rn Concentrations for Analytic Basis of Atmospheric Transport in East Asia

“…Thus, atmospheric 222 Rn has been used for analysis of regional atmospheric transport between continents and oceans. [3][4][5][6][7] Simpler behavior of 222 Rn in the atmosphere is also suitable for validation of numerical models relating to atmospheric transport phenomena. [8][9][10][11] We have established an observation network of continuous measurement of atmospheric 222 Rn concentration in East Asia, where is considered one of the important areas in terms of emission and atmospheric transport of aerosols, yellow dust storms and sorts of air pollutants from rapidly developing megacities, relating to regional health problems, environmental damages and global radiation forcing, i.e., the global warming.…”

Improving land-surface parameterization schemes using stable water isotopes: Introducing the ‘iPILPS’ initiative

“…Biospheric productivity forces a difference between the oxygen isotopes in ocean water and the atmosphere, known as the Dole effect (Dole et al, 1954), so that both water ice and O 2 in ice core air bubbles can be employed to estimate palaeobiospheric productivity. Uranium series isotopes, especially 222 Rn (radon), are useful tracers of land-based processes including the 'continentality' of air masses and the length of subterranean passage of discharging groundwater (e.g., Zahorowski et al, 2005). The age of groundwater is determined using radioisotopes including tritium ( 3 H), sulphur ( 35 S) and carbon ( 14 C), while the stable water isotopes 1 H 1 H 18 O and 1 H 2 H 16 O trace atmospheric, surface and subsurface water processes (e.g., Gat, 1996).…”