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Volume 17, issue 11 | Copyright

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 6797-6811, 2017
https://doi.org/10.5194/acp-17-6797-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 09 Jun 2017

Research article | 09 Jun 2017

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 Sun1,2,5 Wei Du et al.
  • 1State 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

Abstract. Despite extensive studies into the characterization of particle number size distributions at ground level, real-time measurements above the urban canopy in the megacity of Beijing have never been performed to date. Here we conducted the first simultaneous measurements of size-resolved particle number concentrations at ground level and 260m in urban Beijing from 22 August to 30 September. Our results showed overall similar temporal variations in number size distributions between ground level and 260m, 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 a mobility diameter between 100 and 200nm generally showed higher concentrations at higher altitudes. Particle growth rates and condensation sinks were also calculated, which were 3.2 and 3.6nmh−1, and 2.8 × 10−2 and 2.9 × 10−2s−1, at ground level and 260m, 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 (09:00–12:00LT) 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 260m, including a factor associated with new particle formation and growth events (NPEs), and two secondary factors that represent photochemical processing and regional transport. Cooking emission was found to have a large contribution to small particles and showed much higher concentration at ground level than 260m in the evening. These results imply that investigation of NPEs 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.

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We conducted the first simultaneous measurements of size-resolved particle number concentrations at ground level and 260 m in urban Beijing. The vertical differences strongly depend on particle sizes, with accumulation-mode particles being highly correlated at the two heights. We further demonstrated that regional emission controls have a dominant impact on accumulation-mode particles, while the influences on Aitken particles were much smaller due to the enhanced NPF events.
We conducted the first simultaneous measurements of size-resolved particle number concentrations...
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