1. Associate Professor, School of Environmental Science and Engineering, Beijing Normal Univ., Beijing, China 100875.
2. Professor and Dean, College of Environmental Science and Engineering, Beijing Normal Univ., Beijing, China 100875.
3. Professor, China-Canada Center of Energy and Environmental Research, Beijing Normal Univ., Beijing, China 100875. (corresponding author); formerly, Professor and Canada Research Chair, Faculty of Engineering, Univ. of Regina, Regina, Sask, Canada S4S 042.