Influence of mineral dust on changes of 7Be concentrations in air as measured by CTBTO global monitoring system

Publication date: December 2018

Source: Journal of Environmental Radioactivity, Volume 192

Author(s): J. Kuśmierczyk-Michulec, P. Bourgouin

Abstract

Atmospheric Transport Modelling (ATM) results were combined with ⁷Be observations collected during the 2009–2015 period by the three radionuclide stations from the International Monitoring System (IMS), located in Mauritania (18.1 N, 15.9 W), Kuwait (29.3 N, 47.9 E) and Panama (9.0 N, 79.5 W), to study the influence of Saharan dust on changes in ⁷Be surface concentrations. It is demonstrated that for long-range transport (>3000 km), the overall impact of Sahara can be reproduced using a single point source located in the Bodélé depression (17.0 N, 18.0 E). To monitor the arrival time of dust plumes at the IMS stations, a series of 14-day forward simulations with daily releases from the Bodélé, during dusty episodes between 2009 and 2015, were generated. In total 1020 simulations with the output at the surface level (0–150 m) and 420 simulations with the output at 9 vertical layers ranging from the surface up to 10 km, were analysed. In the simulations, the analysed meteorological input data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) were used. It is demonstrated that an influx of dust at high levels (3–10 km) tends to locally increase surface ⁷Be concentrations in area under the influence of subsiding dust plume. It is also shown that an influx of dust at lower altitudes (up to 1 km) will have the opposite effect on surface concentrations. In case dust is present in the whole column of atmosphere, its final impact depends on the ratio between its amount in the upper layers (3–10 km) and lower layers (0–1 km). In consequence an increase up to 30% or a decrease up 20% in daily ⁷Be surface values may be observed during such an episode. On a monthly scale a few episodes related to an increase of ⁷Be values or its decrease may follow each other. It was estimated that on average the presence of dust leads to the increase of ⁷Be mean monthly surface values. The largest increase was noted at the station MRP43, of about 4.1 ± 1.3%; and the smallest at the stations KWP40, of about 2.0 ± 1.6% and PAP50, of about 2.0 ± 1.0%, respectively.

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