Humic acid in ice: Photo-enhanced conversion of nitrogen dioxide into nitrous acid - Bartels-Rausch, Thorsten; Brigante, Marcello; Elshorbany, Yasin F.; Ammann, Markus; D'Anna, Barbara; George, Christian; Stemmler, Konrad; Ndour, Marieme; Kleffmann, Jörg (Atmospheric Environment, 2010)