Macquarie Island hourly radon data set 2013-2020

Brief description

Atmospheric radon observations constitute a convenient and unambiguous indicator of recent terrestrial influence on air masses. Since most anthropogenic gaseous and aerosol pollutants are also of terrestrial origin, high-quality radon observations serve as a proxy for the ‘pollution potential’ of air masses in remote regions (e.g., Chambers et al. 2018; Williams and Chambers 2016).

Radon-222 (radon) is a gaseous decay product of Uranium-238. Its immediate parent, Radium-226, is ubiquitous in soils and rocks. Radon is a noble gas, poorly soluble, and radioactive (t0.5=3.82 d), so it does not accumulate in the atmosphere on greater than synoptic timescales. Its average source function from unfrozen terrestrial surfaces is relatively well constrained, and 2-3 orders of magnitude greater than that from the open ocean. Furthermore, on regional scales radon’s terrestrial source function is not significantly affected by human activity. This combination of physical characteristics enables air masses that have been in contact with terrestrial surfaces to be tracked over the ocean, or within the troposphere, for 2-3 weeks.

The radon concentration of air masses that have been in long-term equilibrium with the Southern Ocean is typically 30-50 mBq m-3 (e.g., Zahorowski et al. 2013). Consequently, key requirements of radon detectors deployed in such remote locations are: a detection limit of ≤50 mBq m-3, stable absolute calibrations, and low maintenance. Macquarie Island is small (34 x 5 km) and situated roughly midway between Australia and Antarctica. Radon and meteorological observations are made at the “Clean Air Laboratory” on an isthmus at the northern end of the island (~54.5 degrees S). At Macquarie Island, radon is measured with a 1500L, single head, dual flow loop, two-filter detector (Whittlestone and Zahorowski 1998). Sample air is drawn at ~45 L m-1 from an inlet ~5 m above ground level (a.g.l.) on a 10 m mast. The detector is automatically calibrated monthly using a 19.58±4% kBq 226Ra source injecting for 6 hours at a flow rate of ~170 cc min-1. Instrumental background checks are performed quarterly by automatically stopping the internal and external flow loop blowers for 24 hours.