Measurements of atmospheric hydrogen peroxide H
2O
2) concentrations over the city of Imizu in Toyama Prefecture, Japan, were performed on November 30, 2016, using a helicopter. The concentrations
of H
2O
2 were highest at high altitudes, while the concentrations of sulfur dioxide (SO
2) and formaldehyde (HCHO) were highest at ground level. The H
2O
2 concentrations were much lower than those measured during summer. The concentrations of H
2O
2 were lower than those of SO
2. SO
2 oxidation in the aqueous phase may be suppressed during late autumn. The calculated H
2O
2 concentration in the atmosphere based on the measured H
2O
2concentrations in new snow at Murododaira (altitude 2450 m), Mt. Tateyama, and on meteorological conditions at the same period were similar to the concentration of H
2O
2 at the high altitude in the helicopter observation. The atmospheric H
2O
2 concentration at a high altitude can be estimated based on the H
2O
2 concentration in new snow at a mountainous site.
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