23 Dec 2021

23 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Measurement report: Vertical profiling of particle size distributions over Lhasa, Tibet: Tethered balloon-based in-situ measurements and source apportionment

Liang Ran1, Zhaoze Deng1, Yunfei Wu1, Jiwei Li1, Zhixuan Bai1, Ye Lu1,2, Deqing Zhuoga3, and Jianchun Bian1,2,4 Liang Ran et al.
  • 1Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 2College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
  • 3Tibet Institute of Plateau Atmospheric and Environmental Science, Lhasa, 850000, China
  • 4College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China

Abstract. In-situ measurements of vertically resolved particle size distributions based on a tethered balloon system were carried out for the first time in the highland city of Lhasa over the Tibetan Plateau in summer 2020, using portable optical counters for the size range of 0.124~32 μm. The vertical structure of 112 aerosol profiles was found to be largely shaped by the evolution of the boundary layer (BL), with a nearly uniform distribution of aerosols within the daytime mixing layer and a sharp decline with the height in the shallow nocturnal boundary layer. During the campaign, the average mass concentration of particulate matters smaller than 2.5 μm in aerodynamic diameter (PM2.5) within the BL was around 3 μg m−3, almost four times of the amount in the free troposphere (FT), which was rarely affected by surface anthropogenic emissions. Though there was a lower level of particle mass in the residual layer (RL) than in the BL, a similarity in particle mass size distributions (PMSDs) suggested that particles in the RL might be of the same origin as particles in the BL. This was also in consistence with the source apportionment analysis based on the PMSDs. Three distinct modes were observed in the PMSDs for the BL and the RL. One mode was exclusively coarse particles up to roughly 15 μm and peaked around 5 μm. More than 50 % of total particle mass was often contributed by coarse mode particles in this area, which was thought to be associated with local dust resuspension. The mode peaking over 0.5~0.7 μm was representative of biomass burning on religious holidays and was found to be most pronounced on holiday mornings. The contribution from the religious burning factor rose from about 25 % on non-holidays to nearly 50 % on holiday mornings. The mode dominated by particles smaller than 0.3 μm was thought to be associated with combustion related emissions and/or secondary aerosol formation. In the FT coarse mode particles only accounted for less than 10 % of the total mass and particles larger than 5 μm were negligible. The predominant submicron particles in the FT might be related to secondary aerosol formation and the aging of existed particles. To give a full picture of aerosol physical and chemical properties and better understand the origin and impacts of aerosols in this area, intensive field campaigns involving measurements of vertically resolved aerosol chemical compositions in different seasons would be much encouraged in the future.

Liang Ran et al.

Status: open (until 03 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-810', Anonymous Referee #2, 07 Jan 2022 reply

Liang Ran et al.


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Short summary
Tibetan Plateau (TP), the highest plateau in the world, plays a crucial role in regional and global climate. To examine the fingerprint left by human activities on the originally remote atmosphere, size distributions of particles from the ground to about 800 m were measured for the first time in summer 2020 in Lhasa, one of few urbanized cities on TP. Potential sources of particles at different heights were explored. The contribution of emissions from religious activities was highlighted.