1. Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
2. Chemistry Department, Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
3. Environmental Protection Department, the Government of the Hong Kong Special Administrative Region, Hong Kong, China
4. Environment Research Institute of Shandong University, Shandong University, Jinan, Shandong 250100, China