This file is in the public domain because it was first published in a Crown Copyright UK government report ("Committee on Air Pollution: Interim Report") in December 1953. According to the UK National Archives: "Crown copyright work which has been published will have copyright protection for 50 years from the end of the year in which the work was published." The report and artwork therefore entered the public domain in January 2004.
This template must not be used to dedicate an uploader's own work to the public domain; CC0 should be used instead.
This work must carry justifications for free usability in both the United States and its country of origin.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.