Vertically resolved characteristics of air pollution during two severe winter haze episodes in urban Beijing, China
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Published:2018-02-20
Issue:4
Volume:18
Page:2495-2509
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Wang Qingqing, Sun YeleORCID, Xu Weiqi, Du WeiORCID, Zhou Libo, Tang Guiqian, Chen Chen, Cheng Xueling, Zhao Xiujuan, Ji DongshengORCID, Han Tingting, Wang Zhe, Li Jie, Wang Zifa
Abstract
Abstract. We conducted the first real-time continuous vertical
measurements of particle extinction (bext), gaseous NO2, and black
carbon (BC) from ground level to 260 m during two severe winter haze
episodes at an urban site in Beijing, China. Our results illustrated four
distinct types of vertical profiles: (1) uniform vertical distributions
(37 % of the time) with vertical differences less than 5 %, (2) higher
values at lower altitudes (29 %), (3) higher values at higher altitudes
(16 %), and (4) significant decreases at the heights of ∼ 100–150 m (14 %). Further analysis demonstrated that vertical convection as
indicated by mixing layer height, temperature inversion, and local emissions
are three major factors affecting the changes in vertical profiles.
Particularly, the formation of type 4 was strongly associated with the
stratified layer that was formed due to the interactions of different air
masses and temperature inversions. Aerosol composition was substantially
different below and above the transition heights with ∼ 20–30 % higher contributions of local sources (e.g., biomass burning and
cooking) at lower altitudes. A more detailed evolution of vertical profiles
and their relationship with the changes in source emissions, mixing layer
height, and aerosol chemistry was illustrated by a case study. BC showed
overall similar vertical profiles as those of bext (R2=0.92 and
0.69 in November and January, respectively). While NO2 was correlated
with bext for most of the time, the vertical profiles of
bext ∕ NO2 varied differently for different profiles, indicating the
impact of chemical transformation on vertical profiles. Our results also
showed that more comprehensive vertical measurements (e.g., more aerosol and
gaseous species) at higher altitudes in the megacities are needed for a
better understanding of the formation mechanisms and evolution of severe
haze episodes in China.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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