Size-resolved effective density of submicron particles during summertime in the rural atmosphere of Beijing, China

Kai Qiao , Zhijun Wu , Xiangyu Pei , Qianyun Liu , Dongjie Shang , Jing Zheng , Zhuofei Du , Wenfei Zhu , Yusheng Wu , Shengrong Lou , Song Guo , Chak K. Chan , Ravi Kant Pathak , Mattias Hallquist , Min Hu


Received August 29, 2017,Revised , Accepted January 16, 2018, Available online February 02, 2018

Volume 30,2018,Pages 69-77

Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm3 for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm3 for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth.

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