Chemical Characteristics and Source Apportionments of Volatile Organic Compounds (VOCs) Before and During the Heating Season at a Regional Background Site in the North China Plain - Han, Tingting; Zhiqiang Ma; Li, Yingruo; Pu, Weiwei; Wu, Jin; Li, Ziming; Shang, Jing; He, Di; Liyan Zhou; Wang, Yao (ATMOSPHERIC RESEARCH, 2021)