Antra Priyadarshi

Evidence of neutron leakage at the Fukushima nuclear plant from measurements of radioactive 35S in California.

A recent earthquake and the subsequent tsunami have extensively damaged the Fukushima nuclear power plant, releasing harmful radiation into the environment. Despite the obvious implication for human health and the surrounding ecology, there are no quantitative estimates of the neutron flux leakage during the weeks following the earthquake. Here, using measurements of radioactive 35S contained in sulfate aerosols and SO2 gas at a coastal site in La Jolla, California, we show that nearly 4 × 1011 neutrons per m2 leaked at the Fukushima nuclear power plant before March 20, 2011. A significantly higher activity as measured on March 28 is in accord with neutrons escaping the reactor core and being absorbed by the coolant seawater 35Cl to produce 35S by a (n, p) reaction. Once produced, 35S oxidizes to and and was then transported to Southern California due to the presence of strong prevailing westerly winds at this time. Based on a moving box model, we show that the observed activity enhancement in is compatible with long-range transport of the radiation plume from Fukushima. Our model predicts that , the concentration in the marine boundary layer at Fukushima, was approximately 2 × 105 atoms per m3, which is approximately 365 times above expected natural concentrations. These measurements and model calculations imply that approximately 0.7% of the total radioactive sulfate present at the marine boundary layer at Fukushima reached Southern California as a result of the trans-Pacific transport.

Resolving the impact of stratosphere‐to‐troposphere transport on the sulfur cycle and surface ozone over the Tibetan Plateau using a cosmogenic 35S tracer

The Himalayas were recently identified as a global hot spot for deep stratosphere-to-troposphere transport (STT) in spring. Although the STT in this region may play a vital role in tropospheric chemistry, the hydrological cycle and aquatic ecosystems in Asia, there is no direct measurement of a chemical stratospheric tracer to verify and evaluate its possible impacts. Here we use cosmogenic S-35 as a tracer for air masses originating in the stratosphere and transported downward. We measure concentrations of S-35 in fresh surface snow and river runoff samples collected from Mount Everest in April 2013 to be more than 10 times higher than previously reported by any surface measurement, in support of the Himalayas as a gateway of springtime STT. In light of this result, measurements of (SO2)-S-35 and (SO42-)-S-35 at Nam Co in spring 2011 are reanalyzed to investigate the magnitudes of stratospheric air masses from the Himalayas to the tropospheric sulfur cycle and surface O-3 level over the Tibetan Plateau. A simple one-box model reveals that the oxidative lifetime of SO2 is reduced in aged STT plumes. Triple oxygen isotopic measurements of sulfate samples suggest that enhanced O-3 levels may shift the oxidation pathway of SO2 in the troposphere, which may be constrained by further intensive sampling and measurements. Comparison with surface O-3 measurements and traditional meteorological tracing methods shows that S-35 is a potentially unique and sensitive tracer to quantify the contribution of stratospheric air to surface O-3 levels in fresh or aged STT plumes.

Cosmogenic 35S measurements in the Tibetan Plateau to quantify glacier snowmelt

The cosmogenic radionuclide ³⁵S (t₁/₂ ~ 87 days) is a unique tracer for high-altitude air mass and has been used extensively to understand stratospheric air mass mixing. In this paper, we investigate if ³⁵S can be utilized as an independent tracer to quantify glacier melt. We report the first measurements of ³⁵S in samples collected from the Tibetan Plateau during 2009–2012 with an aim to interpret ³⁵S in atmospheric particles and their deposition over glacier and snowmelts. Our measurements show that ³⁵S activity in the aerosol phase varies from 116 ± 13 to 2229 ± 52 atoms/m³ resulting in higher values during winter–spring and lower values during summer–autumn. This seasonality is likely due to higher mixing of ³⁵S-rich stratospheric air masses during winter–spring and ³⁵S-poor air masses from the Bay of Bengal during the Asian summer monsoon. The average ³⁵S activity in the Zhadang glacier was found to be 3–8 times higher relative to the nearby lake water. The main source of ³⁵S activity in the Zhadang glacier is atmospheric deposition, whereas both atmospheric deposition and glacier snowmelt are the primary sources in the Nam Co Lake. The focus of this study is to quantitatively determine the spatial and temporal variations in glacier snowmelt. In the future, extensive sampling of aerosols and snow is required for determining ³⁵S in combination with stable oxygen isotopes in sulfate to better understand the glacier melt process and hydrological cycle on the Tibetan Plateau.

Reply to Strub et al.: Chlorine activation by neutrons as an obvious source of 35S at Fukushima

Strub et al. (1) provide comments on our paper (2) largely based on data from operational reactors, whereas the reactor at Fukushima was overwhelmed by a 19-ft wave and tidal surge resulting in massive damage and partial core meltdown that our measurements captured. The comments are mostly irrelevant, and we quantitatively address them. The observation of the 35SO42− peak at La Jolla derived from intense meteorological conditions at Fukushima producing long-range transport of the radiation plume to California (3), and the air mass back trajectories confirm that 35S was produced at Fukushima. Our prediction, overlooked by Strub et al. (1), of the possibility of reactor core …