1. Michigan Technological University, Houghton, Michigan 49931, United States
2. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
3. National Institute of Aerospace, Hampton, Virginia 23666, United States
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
5. Institute of Volcanology and Risk Assessment─IVAR, Rua da Mãe de Deus, Ponta Delgada 9500-321, Portugal