Consumption of CH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Cl, CH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Br and CH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;I and emission of CHCl&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;, CHBr&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Br&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from a retreating Arctic glacier's forefield