1. Department of Chemistry, Umeå University, SE- 90187 Umeå, Sweden
2. School of Science and Technology, Örebro University, SE-70182 Örebro, Sweden
3. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
4. Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901, United States