Geophysical Institute and Department of Chemistry, University of Alaska Fairbanks, Fairbanks, AK 99775-6160, USA

Geophysical Institute and Department of Chemistry, University of Alaska Fairbanks, Fairbanks, AK 99775-6160, USA

Geophysical Institute and Department of Chemistry, University of Alaska Fairbanks, Fairbanks, AK 99775-6160, USA

Institute for Environmental Physics, University of Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany

deceased

U.S. Army Cold Regions Research and Engineering Laboratory, P.O. Box 35170, Fort Wainwright, AK 99703-0170, USA

U.S. Army Cold Regions Research and Engineering Laboratory, P.O. Box 35170, Fort Wainwright, AK 99703-0170, USA

U.S. Army Cold Regions Research and Engineering Laboratory, P.O. Box 35170, Fort Wainwright, AK 99703-0170, USA

Institute for Environmental Physics, University of Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany