CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, δO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;/N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and APO: observations from the Lutjewad, Mace Head and F3 platform flask sampling network