NUCLIM

Project NuClim (Nuclear observations to improve Climate research and greenhouse gases [GHG] emission estimates) aims to use high-quality measurements of atmospheric radon activity concentration and ambient radioactivity to advance climate science and to improve radiation protection and nuclear surveillance capabilities.

Radon (Rn-222) is a unique atmospheric tracer, since it is an inert gaseous radionuclide with a predominantly terrestrial source and a short half-life (3.8232 (8) d), enabling quantification of the relative degree of recent (< 21 d) terrestrial influences on marine air masses. The NuClim campaign at the Eastern North Atlantic (ENA) ARM observatory located on Graciosa Island (Azores) will establish continuous (30-min) atmospheric radon activity concentration (referred to as radon) measurements using the most sensitive instrument currently available, the ANSTO 1500 L two-filter dual-flow-loop radon monitor, capable of accurately measuring the very low levels of radon typical of remote marine boundary-layer air masses. These measurements will provide an objective means by which to quantify the degree of recent terrestrial influence on marine air masses, and therefore assist diverse climate and environmental studies.

The radon-based classification of air mass origin, combined with measurements of aerosols and clouds, enables the characterization of aerosols and cloud properties in relation to the degree of recent terrestrial influence (or “pollution potential”) of the host air masses, supporting interpretation of atmospheric observations of trace gases, aerosols, and clouds, and enabling improved quantification of the contributions of both remote terrestrial pollution events and marine biological processes to the composition of the marine atmospheric boundary layer.

High-quality (Integrated Carbon Observations System - ICOS-compliant) measurements of atmospheric carbon dioxide (CO2) and methane (CH4),mixing ratios will be performed in the NuClim campaign using a cavity ring-down spectrometer (CRDS; Picarro Inc., USA). The simultaneous measurement of atmospheric radon concentration and GHGs will enable baseline observations of GHGs from marine air masses least influenced by terrestrial sources, representative of hemispheric background values. These observations will enable NuClim to provide an accurate time-varying baseline reference level for European GHG concentrations based on nuclear observations, enabling clearer distinction between local- and regional-scale emissions and slowly changing background levels. Observations performed over NuClim’s 40-month duration will constitute the beginning of a highly accurate long-term characterization of trends in mid-latitude Northern Hemisphere baseline concentrations of CO2 and CH4, helping to reduce uncertainties in global climate change projections. NuClim will also begin characterizing the seasonality and inter-annual behavior of radon concentrations in the marine boundary layer of the North Atlantic Ocean to assist the evaluation of transport and convective mixing schemes of global climate and chemical transport models.

The direct NuClim atmospheric radon measurements will be complemented by indirect (by progeny) measurements enabling improved quantification of the background variability in ambient gamma dose rate driven by meteorological factors, contributing to the improvement of the performance of nuclear surveillance networks for radiological protection purposes. Indirect radon measurements will be performed by sampling air pumped through glass-fiber filters, with the beta emissions of the radon progeny accumulated on the filters recorded with Geiger-Müller counters. The filters are further analyzed in the laboratory, yielding regular (weekly) observations of cosmogenic Be-7 and long-lived Pb-210 radionuclides. Spectral gamma radiation measurements will also be performed with a NaI(Tl) scintillator detector and a LaBr2/CeBr2-spectral-dosemeter, improving understanding of atmospheric wet deposition and natural variability of ambient gamma radiation and supporting historical (non-spectral) gamma radiation measurements that have been conducted at ENA since 2015. Ionizing radiation studies are further complemented by measurement of the concentration and average mobility of positive and negative cluster ions using a cluster ion counter.

The NuClim campaign will implement new nuclear measurement capabilities at the ENA ARM site. The new observations have multiple uses in climate and environmental monitoring, ensuring a long-lasting impact of the field campaign.

PI: Susana Barbosa

Co-Investigators: Scott Chambers, Jussi Paatero, Anca Melintescu, Stefan Roettger, Joana Ramos, Eduardo Azevedo, Damien Martin, Xuemeng Chen, Krzysztof Fortuniak, Dafina Kikaj, Angelina Wenger

Timeline