Wintertime photochemistry in Beijing: observations of RO<sub><i>x</i></sub> radical concentrations in the North China Plain during the BEST-ONE campaign
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Published:2018-08-27
Issue:16
Volume:18
Page:12391-12411
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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:
Tan ZhaofengORCID, Rohrer Franz, Lu KedingORCID, Ma Xuefei, Bohn BirgerORCID, Broch SebastianORCID, Dong Huabin, Fuchs HendrikORCID, Gkatzelis Georgios I., Hofzumahaus AndreasORCID, Holland Frank, Li XinORCID, Liu YingORCID, Liu Yuhan, Novelli AnnaORCID, Shao Min, Wang HaichaoORCID, Wu YushengORCID, Zeng Limin, Hu Min, Kiendler-Scharr AstridORCID, Wahner AndreasORCID, Zhang Yuanhang
Abstract
Abstract. The first wintertime in situ
measurements of hydroxyl (OH), hydroperoxy (HO2) and organic peroxy
(RO2) radicals
(ROx=OH+HO2+RO2) in combination
with observations of total reactivity of OH radicals, kOH in
Beijing are presented. The field campaign “Beijing winter finE particle
STudy – Oxidation, Nucleation and light Extinctions” (BEST-ONE) was
conducted at the suburban site Huairou near Beijing from January to
March 2016. It aimed to understand oxidative capacity during wintertime and
to elucidate the secondary pollutants' formation mechanism in the North China
Plain (NCP). OH radical concentrations at noontime ranged from 2.4×106cm-3 in severely polluted air (kOH∼27s-1) to 3.6×106cm-3 in relatively clean
air (kOH∼5s-1). These values are nearly 2-fold
larger than OH concentrations observed in previous winter campaigns in
Birmingham, Tokyo, and New York City. During this campaign, the total primary
production rate of ROx radicals was dominated by the
photolysis of nitrous acid accounting for 46 % of the identified primary
production pathways for ROx radicals. Other important
radical sources were alkene ozonolysis (28 %) and photolysis of
oxygenated organic compounds (24 %). A box model was used to simulate the
OH, HO2 and RO2 concentrations based on the observations
of their long-lived precursors. The model was capable of reproducing the
observed diurnal variation of the OH and peroxy radicals during clean days
with a factor of 1.5. However, it largely underestimated HO2 and
RO2 concentrations by factors up to 5 during pollution episodes.
The HO2 and RO2 observed-to-modeled ratios increased with
increasing NO concentrations, indicating a deficit in our understanding of
the gas-phase chemistry in the high NOx regime. The OH
concentrations observed in the presence of large OH reactivities indicate
that atmospheric trace gas oxidation by photochemical processes can be highly
effective even during wintertime, thereby facilitating the vigorous formation
of secondary pollutants.
Funder
National Natural Science Foundation of China European Commission
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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