Simultaneous measurements of particle number size distributions at ground level and 260 m on a meteorological tower in urban Beijing, China
Wei Du1,2, Jian Zhao1,2, Yuying Wang3, Yingjie Zhang1,4, Qingqing Wang1, Weiqi Xu1,2, Chen Chen1, Tingting Han1,2, Fang Zhang3, Zhanqing Li3, Pingqing Fu1,5, Jie Li1, Zifa Wang1,5, and Yele Sun1,51State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 2College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 3College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China 4School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China 5Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
Received: 29 Nov 2016 – Accepted for review: 27 Dec 2016 – Discussion started: 02 Jan 2017
Abstract. Despite extensive studies into characterization of particle number size distributions at ground level, real-time measurements above the urban canopy in the megacity of Beijing has never been performed to date. Here we conducted the first simultaneous measurements of size-resolved particle number concentrations at ground level and 260 m in urban Beijing from 22 August to 30 September. Our results showed overall similar temporal variations in number size distributions between ground level and 260 m, yet periods with significant differences were also observed. Particularly, accumulation mode particles were highly correlated (r2 = 0.85) at the two heights while Aitken mode particles presented more differences. Detailed analysis suggests that the vertical differences in number concentrations strongly depended on particle size, and particles with mobility diameter between 100–200 nm generally showed higher concentrations at higher altitudes. Particle growth rates and condensation sinks were also calculated which were 3.2 and 3.6 nm h−1, and 2.8 × 10−2 and 2.9 × 10−2 s−1, at ground level and 260 m, respectively. By linking particle growth with aerosol composition, we found that organics appeared to play an important role in the early stage of the growth (9:00–12:00) while sulfate was also important during the later period. Positive matrix factorization of size-resolved number concentrations identified three common sources at ground level and 260 m including a factor associated with new particle formation and growth events (NPE), and two secondary factors that represent photochemical processing and regional transport, respectively. Cooking emission was found to have a large contribution to small particles, and showed much higher concentration at ground level than 260 m at dinner time. This result has significant implications that investigation of NPE at ground level in megacities needs to consider the influences of local cooking emissions. The impacts of regional emission controls on particle number concentrations were also illustrated. Our results showed that regional emission controls have a dominant impact on accumulation mode particles by decreasing gas precursors and particulate matter loadings, and hence suppressing particle growth. In contrast, the influences on Aitken particles were much smaller due to the enhanced new particle formation (NPF) events.
Du, W., Zhao, J., Wang, Y., Zhang, Y., Wang, Q., Xu, W., Chen, C., Han, T., Zhang, F., Li, Z., Fu, P., Li, J., Wang, Z., and Sun, Y.: Simultaneous measurements of particle number size distributions at ground level and 260 m on a meteorological tower in urban Beijing, China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1064, in review, 2017.