In the terrestrial atmosphere, the presence of iodine, a nutrient element, is important in determining the prevalence of iodine deficiency disorders. Since oceanic iodine emissions decrease as sea surface temperature drops,the contributors to atmospheric iodine vary from oceanic sources in summer to other sources in winter. These sources and their respective contributions are of great importance, but have remained unexplored.
Researchers from the Institute of Earth Environment of the Chinese Academy of Sciences investigated the source terms of iodine in atmospheric particulate matter by analyzing daily PM2.5 samples collected for one month from four metropolises of China.
They found that the PM2.5 samples from Changchun, Beijing and Chengdu had a clear source profile composed of dust, coal, and fuel oil, while samples from Hong Kong showed an indistinguishable signature, which was due to the mixing of road dust and oceanic materials. All the profiles of coal and fuel oil correspond to a relatively higher concentration of iodine.
Coincidentally, this pattern was perfectly examined by the analytical data of the atomic ratio of 129I to 127I, where the ratios decreased with an increasing contribution of coal and fuel oil, and increased when the contribution of dust was dominant. This is consistent with the isotopic characteristics of iodine, which differ greatly between nuclear activity and fossil fuels such as coal and petroleum, which formed millions to billions of years ago and are therefore depleted in 129I.
They also found, for the first time, that in winter inland areas, fuel oil, together with coal combustion, was a significant source of atmospheric iodine.
This study enhances the understanding of the impact of human activities on environmental iodine levels, and is crucial for providing a complete picture of the iodine geochemistry, to better understand the iodine deficiency-related health problems and the stratospheric ozone depletion.
