The spread and abatement of the aerosol injected into the stratosphere by the explosion of Katmai volcano in Alaska on June 6, 1912, have been investigated. The spread of the dust veil and twilight observations are discussed. Turbidity was determined from solar radiation data obtained mainly in central and northern Europe and the United States. In Europe, volcanic turbidity was quite large but highly variable during the summer of 1912 and became rather low in February 1913, when it was still high over the United States. Temporary presence of Katmai dust over Mexico City is very questionable, so that increased turbidity over Peru during 1913 may have had other causes. The turbidity disappeared rather suddenly in late 1914. Average residence time of the dust was nearly 1 year.