Understanding radioactive Cs contamination has been a central issue at Fukushima Daiichi and other nuclear legacy sites; however, atomic -scale characterization of radioactive Cs in environmental samples has never been achieved. Here we report, for the first time, the direct imaging of radioactive Cs atoms using high -resolution high -angle annular dark -field scanning transmission electron microscopy (HAADF-STEM). In Cs -rich microparticles collected from Japan, we document inclusions that contain 27 - 36 wt% of Cs (reported as Cs 2 O) in a zeolite: pollucite. The compositions of three pollucite inclusions are (Cs 1.86 K 0.11 Rb 0.19 Ba 0.22 ) 2.4 (Fe 0.85 Zn 0.84 X 0.31 ) 2.0 Si 4.1 O 12 , (Cs 1.19 K 0.05 Rb 0.19 Ba 0.22 ) 1.7 (Fe 0.66 Zn 0.32 X 0.41 ) 1.4 Si 4.6 O 12 , and (Cs 1.27 K 0.21 Rb 0.29 Ba 0.15 ) 1.9 (Fe 0.60 Zn 0.32 X 0.69 ) 1.6 Si 4.4 O 12 (X includes other cations). HAADF-STEM imaging of pollucite, viewed along the [111] zone axis, revealed an array of Cs atoms, which is consistent with a simulated image using the multi -slice method. The occurrence of pollucite indicates that locally enriched Cs reacted with siliceous substances during the Fukushima meltdowns, presumably through volatilization and condensation. Beta radiation doses from the incorporated Cs are estimated to reach 10 6 - 10 7 Gy, which is more than three orders of magnitude less than typical amorphization dose of zeolite. The atomic -resolution imaging of radioactive Cs is an important advance for better understanding the fate of radioactive Cs inside and outside of nuclear reactors damaged by meltdown events.

The impact of water droplets on soils has recently been found to drive emissions of airborne soil organic particles (ASOP). The chemical composition of ASOP include macromolecules such as polysaccharides, tannins, and lignin (derived from degradation of plants and biological organisms), which determine light absorbing (brown carbon) particle properties. Optical properties of ASOP were inferred from the quantitative analysis of the electron energy-loss spectra acquired over individual particles using transmission electron microscopy. The optical constants of ASOP are compared with those measured for laboratory generated particles composed of Suwanee River Fulvic Acid (SRFA) reference material, which is used as a laboratory surrogate of ASOP. The chemical composition of the particles was analyzed using energy dispersive X-ray spectroscopy, electron energy-loss spectroscopy, and synchrotron-based scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy. ASOP and SRFA exhibit similar carbon composition, with minor differences in other elements present. When ASOP are heated to 350 degrees C their absorption increases as a result of pyrolysis and partial volatilization of semivolatile organic constituents. The retrieved refractive index (RI) at 532 nm of SRFA particles, ASOP, and heated ASOP were 1.22-0.07i, 1.29-0.07i, and 1.90-0.38i, respectively. Retrieved imaginary part of the refractive index of SRFA particles derived from EELS measurements was higher and the real part was lower compared to data from more common optical methods. Therefore, corrections to the EELS data are needed for incorporation into models. These measurements of ASOP optical constants confirm that they have properties characteristic of atmospheric brown carbon and therefore their potential effects on the radiative forcing of climate need to be assessed in atmospheric models.