Temporal variations, sources and tracer significance of Polonium-210 in the metropolitan atmosphere of Beijing, China

In the present study, Polonium-210 (Po-210) is studied in TSP and coal combustion samples for its potential application in tracing air pollutants. A significant seasonal variation of atmospheric Po-210 in Beijing was observed: winter > autumn > summer > spring. During the combustion of coal, Po-210 was highly enriched in fly ash but was depleted in bottom ash. Using selenium (Se) as an indicator of coal combustion, significantly positive correlation between Po-210 and Se in TSP samples (r(2) = 0.705) revealed that coal combustion was a primary source of atmospheric Po-210 in Beijing. The mean emission factor of Po-210 from industry sector was found to be the highest (1.15 Bq kg(-1)), followed by the residential (0.308 Bq kg(-1)) and coal-fired power plant (0.0776 Bq kg(-1)) sectors. The annual emission inventories of Po-210 from three coal consumer sectors (residential, coal-fired power plant, and industry) in 2016 in Beijing were estimated to be 1.49, 0.0729, and 1.36 GBq, respectively. The ratio of radioactive Po-210 and stable element Se (Po-210/Se) was creatively used as a combined indicator or fingerprint of coal combustion emission, which will contribute to the development of radioisotope tracer technology based on nuclide fingerprint database in the source identification of air pollutants.