In the beginning of April 2020, large fires that started in the Chernobyl Exclusion Zone (CEZ) established after the Chernobyl accident in 1986 caused media and public concerns about the health impact from the resuspended radioactivity. In this paper, the emissions of previously deposited radionuclides from these fires are assessed and their dispersion and impact on the population is examined relying on the most recent data on radioactive contamination and emission factors combined with satellite observations. About 341 GBq of ¹³⁷Cs, 51 GBq of ⁹⁰Sr, 2 GBq of ²³⁸Pu, 33 MBq of ²³⁹Pu, 66 MBq of ²⁴⁰Pu and 504 MBq of ²⁴¹Am were released in 1^st–22^nd April 2020 or about 1,000,000,000 times lower than the original accident in 1986 and mostly distributed in Central and East Europe. The large size of biomass burning particles carrying radionuclides prevents long-range transport as confirmed by low concentrations reported in Europe. The highest cumulative effective doses (>15 μSv) were calculated for firefighters and the population living in the CEZ, while doses were much lower in Kiev (2–5 μSv) and negligible in Europe. All doses are radiologically insignificant and no health impact on the European population is expected from the April 2020 fires.

Emissions were calculated with three methods.

Method 1 (bottom-up) uses burned area, based on a modified method from [Stohl et al., 2007], and MODIS active fires with the maximum confidence level (100%) combined with a statistical approach [Wotawa et al., 2006]. Then, we use the most recently updated emission factors (EFs) for radionuclides [Hao et al., 2018] together with ground contamination data [Kashparov et al., 2001, 2003, 2018] from the CEZ (Fig. S 2, Fig. S 3).

Method 2 (top-down) combines EFs of ¹³⁷Cs (in gr species per kg of dry mass burned) from [Hao et al., 2018] with combusted biomass (in kg of dry mass) from Copernicus Atmosphere Monitoring Service (CAMS) Global Fire Assimilation System (GFAS) [Kaiser et al., 2012].

Method 3 (top-down) uses experimental ratios of ¹³⁷Cs with particulate organic matter (POM) from [Strode et al., 2012] for boreal regions and calculates emissions using POC from CAMS GFAS [Kaiser et al., 2012].

Emissions calculated from the three different methods were ingested to the Lagrangian particle transport model FLEXPART (Flexible Particle Dispersion Model) version 10.4 [Pisso et al., 2019] that simulated transport and deposition of ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am.

A preliminary assessment on the committed internal (inhalation) and external (air submersion/immersion and deposition) exposure has been conducted for four population groups (1-year old infants, 10-year old children, adults and workers/firefighters). The methodology is based on the[WHO, 2012] report for Fukushima and includes the most recent updates on dose calculations. 

Preprocessing.tar includes MODIS active fires from 1-22 April, contamination data for ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am and CAMS GFAS POC and FRP that were used to calculate emissions with 3 methods. The Python scripts used to calculate emissions and create the RELEASES files for FLEXPART model are also included.

FLEXPART_forward.tar includes all FLEXPART output netCDF files, in which the transport and deposition of ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am were simulated.

FLEXPART_backward.tar includes all FLEXPART output binary files that prove that the origin of air masses when measurements of radioactivity were carried out was directly from the Chernobyl Exclusion Zone. Three receptor points were investigated, namely Thessaliniki, Vienna International Centre (VIC) and Kiev. Each output is linked to a specific particle size distribution for the species as explained in the manuscript.

Postprocessing.tar consists of all python scripts to create the figures and videos of the manuscript including those that were used for validation of the model and for the dosimetric assessment.