of 16
S1
Supplementary Information for
Increasing Contribution of Chlorine Chemistry to
Wintertime Ozone Formation Promoted by Enhanced
Nitrogen Chemistry
Gaojie Chen
1,7,8
, Lingling Xu
1,7
, Shaocai Yu
2,9,10
*, Likun Xue
3
, Ziyi Lin
1,7,8
, Chen
Yang
1,7,8
, Xiaoting Ji
1,7,8
, Xiaolong Fan
1,7
*, Yee Jun Tham
4
, Haichao Wang
5
, Youwei
Hong
1,7
, Mengren Li
1,7
, John H.
Seinfeld
6
, Jinsheng Chen
1,7
*
1
Center for Excellence in Regional Atmospheric Environment, Institute of Urban
Environment, Chinese Academy of Sciences, Xiamen 361021, China
2
Zhejiang Province Key Laboratory of Solid Waste Treatment and Recycling; School
of Environmental Sciences and Engineering, Zhejiang Gongshang University,
Hangzhou
310018, China
3
Environment Research Institute, Shandong University, Qingdao 266237, China
4
School of Marine Sciences, Sun Yat-sen University, Zhuhai 519082, China
5
School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
6
Division of Chemistry and Chemical Engineering, California Institute of Technology,
Pasadena, CA 91125, USA
7
Fujian Key Laboratory of Atmospheric Ozone Pollution Prevention, Institute of Urban
Environment, Chinese Academy of Sciences, Xiamen 361021, China
8
University of Chinese Academy of Sciences, Beijing 100049, China
9
Collaborative Innovation Center for Statistical Data Engineering Technology and
Application; School of Statistics and Mathematics, Zhejiang Gongshang University,
Hangzhou 310018, China
10
Research Center for Air Pollution and Health; Key Laboratory of Environmental
Remediation and Ecological Health, Ministry of Education, College of Environment
and Resource Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, P.R. China
*Corresponding
authors
E-mail:
jschen@iue.ac.cn
(Jinsheng
Chen);
shaocaiyu@zjgsu.edu.cn (Shaocai Yu);
xlfan@iue.ac.cn (Xiaolong Fan).
Numbers of Text: 5
Numbers of Figures: 7
Numbers of Tables: 3
Total pages: 16
S2
This file includes:
Supplementary Texts
Text S1.
The instruments of field observation.
Text S2.
The calibrations for ClNO
2
, N
2
O
5
, and Cl
2
.
Text S3.
Output parameters for the box model.
Text S4.
Calculation of aerosol pH using ISORROPIA-II.
Text S5.
Co-generation mechanisms of Cl
2
and ClNO
2
.
Supplementary Figures
Figure S1.
The sensitivities of Cl
2
, ClNO
2
, and N
2
O
5
to RH under different RH
conditions.
Figure S2.
The average diurnal profiles of BLH, UV,
J
NO
2
, NO
2
, and NO during and
after the Spring Festival at our study site.
Figure S3.
Correlations between NO
2
and nitrate (NO
3
) during the daytime (A), and
correlations between N
2
O
5
and the values of NO
2
× O
3
(approximately the production
rates of NO
3
radicals) during the nighttime at our study site (B).
Figure S4.
Oxidation of VOCs. The contributions of different VOC groups oxidized
by Cl radicals during the Spring Festival (A) and after the Spring Festival (B). The
contributions of different atmospheric oxidants (including OH, Cl, NO
3
, and O
3
) to
different VOC groups during the Spring Festival (C) and after the Spring Festival (D).
Comparisons of alkane oxidation rates (molecules·cm
-3
·s
-1
) by OH and Cl radical
during the Spring Festival (E). Comparisons of alkane oxidation rates by OH and Cl
radicals (molecules·cm
-3
·s
-1
) after the Spring Festival (F).
Figure S5.
RO
x
production rates through different pathways during the Spring Festival
(A) and after the Spring Festival (B).
Figure S6.
The percentages of average daytime increase in the values of OH, HO
2
, RO
2
radicals, net O
3
production rates (NP(O
3
)), and AOC induced by chlorine chemistry
during and after the Spring Festival.
Figure S7.
(A–F) Correlations among daytime increasement levels of O
3
and increased
percentages of Cl
2
(A), ClNO
2
(B), HO
2
radicals (C), RO
2
radicals (D), net O
3
production rates (NP(O
3
)) (E), and AOC (F) induced by chlorine chemistry during and
after the Spring Festival.
Supplementary Tables
Table S1.
Techniques of measurement, time resolutions, detection limits of instruments
during the whole observation period.
Table S2.
Summary of ClNO
2
and Cl
2
peak concentrations in China (Unit: ppt).
Table S3.
Comparisons of observed parameters between during and after the Spring
Festival using the t-test. At the 0.05 level, there is a significant difference in the mean
values of parameters between during and after the Spring Festival.
S3
Text S1.
The instruments of field observation.
This atmospheric observation Supersite (over 70 meters above the ground) at
Institute of Urban Environment, Chinese Academy of Sciences was equipped with
complete instruments designed for the detection of gaseous pollutants, aerosol
components, and meteorological parameters.
1-4
Trace gases, NO
x
(NO
2
and NO), CO,
O
3
, and SO
2
, were measured by employing continuous gas analyzers manufactured by
Thermo Fisher Scientific, USA (TEI 42
i
, 48
i
, 49
i
, and 43
i
). PM
2
.
5
mass concentrations
were monitored by using the tapered element oscillating microbalance (TEOM1405)
from Thermo Scientific Corp., MA, USA. The particle surface area concentrations (
S
a
)
were calculated based on the ambient particle number size distribution measured with
the Scanning Mobility Particle Sizer (SMPS, TSI Inc.) and Aerodynamic Particle Size
Spectrometer (APS).
5
Inorganic ion components of PM
2.5
were detected by the Monitor
for AeRosols and Gases in ambient Air (MARGA; model ADI 2080) from Applikon
Analytical B.V., the Netherlands. Photolysis rates (including
J
(O
1
D),
J
(NO
2
),
J
(HONO),
J
(NO
3
),
J
(HCHO), and
J
(H
2
O
2
)) were measured by a photolysis
spectrometer (model PFS-100) provided by Focused Photonics Inc., Hangzhou, China.
Other meteorological parameters, including air temperature (T), atmospheric pressure
(P), relative humidity (RH), wind direction (WD), wind speed (WS), and ultraviolet
radiation (UV) were also measured by the weather station equipped with a sonic
anemometer (150WX) from Airmar, USA. The boundary layer height (BLH) was
obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF)
ERA5 hourly reanalysis dataset. In addition, HCHO was detected by the HCHO
analyzer (model FMS-100) from Focused Photonics Inc., Hangzhou, China. A gas
chromatography system equipped with a mass spectrometer and flame ionization
detector (GC-MS/FID, TH-300B, Wuhan, China) was employed to measure VOC
species (including alkanes, alkenes, alkynes, aromatics, oxygenated VOCs (OVOCs),
and halocarbons). PAN was detected by a PAN analyzer (PANs-1000, Focused
Photonics Inc., Hangzhou, China) equipped with the gas chromatography-electron
capture detector (GC-ECD).
Text S2.
The calibrations for ClNO
2
, N
2
O
5
, and Cl
2
.
The calibration procedure for measuring ClNO
2
sensitivity has been described in
detail in previous studies.
6-8
In brief, a nitrogen (N
2
) flow at a rate of 50 mL·min
−1
,
containing 6 ppm of Cl
2
, was directed over a slurry composed of sodium nitrite (NaNO
2
)
and sodium chloride (NaCl). This slurry facilitated the production of ClNO
2
, with NaCl
being presented to minimize the formation of nitrogen dioxide (NO
2
) as a secondary
product. Subsequently, the resultant mixture containing ClNO
2
was conditioned to a
specified relative humidity (RH) and then sampled using the CIMS instrument. To
quantify the concentrations of ClNO
2
, the mixture was either directly fed into a cavity
attenuated phase shift spectroscopy (CAPS) instrument to measure the baseline levels
of NO
2
, then it was passed through a thermal dissociation tube heated to 380
°C
, causing
ClNO
2
to decompose into NO
2
. The overall concentrations of NO
2
were then
determined utilizing the CAPS instrument. The difference of the measured NO
2
S4
concentrations between with and without thermal dissociation, corresponded to the
concentrations of ClNO
2
. For the calibration of N
2
O
5
, O
3
was generated by passing
approximately 30 sccm of ultrapure zero air through a mercury lamp (UVP). O
3
then
reacted with a 30 sccm flow rate of NO
2
, producing NO
3
, which subsequently reacted
with NO
2
to yield a flow of N
2
O
5
. This N
2
O
5
-enriched flow was utilized to calibrate the
CIMS measurements of N
2
O
5
. By adjusting the humidity, a mixed flow containing
stable N
2
O
5
was introduced into the CIMS instrument, allowing for the acquisition of a
normalized humidity-dependent curve for N
2
O
5
. Although the absolute concentrations
of the N
2
O
5
source were not directly quantified due to the absence of an N
2
O
5
-specific
detector, the N
2
O
5
-enriched flow was passed through a supersaturated sodium chloride
solution.
9, 10
Cl
2
standard gas was generated by employing a continuous flow of ultra-
pure N
2
(0.1 SLPM) which directed through a Cl
permeation tube (manufactured by
VICI Metronics, Inc.) and maintained at a temperature of 40
°C
. The Cl
2
permeation
rate was determined as 98 ng/min. The resulting effluent from the permeation tube was
subsequently subjected to additional dilution using an adjustable secondary flow
(varied as necessary) to effectively control the concentrations of Cl
.
Text S3.
Output parameters for the box model.
(1) Calculation of O
3
production and loss rates including Cl-related reactions.
O
3
production and loss rates were calculated to obtain the net O
3
production rates. The
O
3
production pathways include HO
2
+ NO and RO
2
+ NO, and the Cl-related reactions
producing NO
2
(S1-S6). The O
3
loss pathways include NO
2
+ OH/RO
2
, O
3
photolysis,
O
3
+ OH, O
3
+ HO
2
, O
3
/NO
3
+ VOCs, and the Cl-related reactions consuming NO
2
(Eqs. S1-S6).
ClNO
2
+ h
v
Cl + NO
2
(S1)
ClONO
2
+ h
v
ClO + NO
2
(S2)
ClO + NO
Cl + NO
2
(S3)
Cl + O
3
ClO + O
2
(S4)
ClO + NO
2
ClONO
2
(S5)
Cl + NO
2
ClNO
2
(S6)
(2) Calculation of AOC.
AOC is calculated d by the sum of the rates of CH
4
, CO, and VOCs oxidized by
atmospheric oxidants (O
3
, OH, Cl and NO
3
),
11, 12
shown as Eq. (S7).
퐴푂퐶
=
[
]
[푋
]
(S7)
Where, [
] represents the concentrations of reduced species (VOCs, CO, and CH
4
), [
X
]
is the concentrations of atmospheric oxidants (OH, Cl, NO
3
, and O
3
), and
푌푖
is the
reaction rate constant of
and
X
.
Text S4.
Calculation of aerosol pH using ISORROPIA-II.
The aerosol pH was calculated by Eq S8 based on a thermodynamic equilibrium
model (ISORROPIA-II):
S5
푝퐻
=
log
10
1000
+
퐴퐿푊퐶
(S8)
Here, H
+
is the hydronium ion concentrations per volume of air (μg·m
-3
), and ALWC
is the aerosol liquid water contents (μg·m
-3
). The model was constrained by the NH
4
+
-
NO
3
-Cl
-SO
4
2−
-Na
+
-K
+
-NH
3
-HNO
3
-HCl system (measured by the MARGA), as well
as temperature and relative humidity with a one-hour time resolution. The model setup
is similar to the previous studies.
13, 14
In brief, it was run in the “forward” mode, and
the total concentrations (gas + particle) of specific species were input into the model
for the calculations. Particles were considered as be “metastable”, where salts did not
precipitate under supersaturated conditions.
Text S5.
Co-generation mechanisms of Cl
2
and ClNO
2
.
Eqs. S9-S18 present the co-generation mechanisms of Cl
2
and ClNO
2
in the previous
work.
15
NO
3
+ H
+
+ h
v
NO
2
+ OH
(S9)
NO
3
+ h
v
NO
2
+ O(
3
P)
(S10)
OH + Cl
HOCl
(S11)
HOCl
+ H
+
H
2
O + Cl
(S12)
O(
3
P) + Cl
O
+ Cl
(S13)
Cl + Cl
Cl
2
(S14)
2Cl
2
Cl
2
+ 2Cl
(S15)
Cl
2
+ H
2
O
HOCl + Cl
+ H
+
(S16)
Cl
2
+ NO
2
ClNO
2
+ Cl
(S17)
HOCl + NO
2
ClNO
2
+ OH
(S18)
S6
Figure S1.
The sensitivities of Cl
2
, ClNO
2
, and N
2
O
5
to RH under different RH
conditions.
S7
Figure S2.
The average diurnal profiles of BLH, UV,
J
NO
2
, NO
2
, and NO during and
after the Spring Festival at our study site.
S8
Figure S3.
Correlations between NO
2
and nitrate (NO
3
) during the daytime (A), and
correlations between N
2
O
5
and the values of NO
2
× O
3
(approximately the production
rates of NO
3
radicals) during the nighttime at our study site (B).
S9
Figure S4.
Oxidation of VOCs. The contributions of different VOC groups oxidized
by Cl radicals during the Spring Festival (A) and after the Spring Festival (B). The
contributions of different atmospheric oxidants (including OH, Cl, NO
3
, and O
3
) to
different VOC groups during the Spring Festival (C) and after the Spring Festival (D).
Comparisons of alkane oxidation rates (molecules·cm
-3
·s
-1
) by OH and Cl radical
during the Spring Festival (E). Comparisons of alkane oxidation rates by OH and Cl
radicals (molecules·cm
-3
·s
-1
) after the Spring Festival (F).
S10
Figure S5.
RO
x
production rates through different pathways during the Spring Festival
(A) and after the Spring Festival (B).
Figure S6.
The percentages of average daytime increase in the values of OH, HO
2
, RO
2
radicals, net O
3
production rates (NP(O
3
)), and AOC induced by chlorine chemistry
during and after the Spring Festival.
S11
Figure S7.
(A–F) Correlations among daytime increasement levels of O
3
and increased
percentages of Cl
2
(A), ClNO
2
(B), HO
2
radicals (C), RO
2
radicals (D), net O
3
production rates (NP(O
3
)) (E), and AOC (F) induced by chlorine chemistry during and
after the Spring Festival.
S12
Table S1.
Techniques of measurement, time resolutions, detection limit of instruments
during the whole observation period.
Parameters
Techniques
Time resolutions
Limit of detection
Cl
2
, ClNO
2
, and
N
2
O
5
I
-ToF-CIMS
1 min
~ 1 ppt
CH
4
NCMS6300
15 min
21 ppb
VOCs
GC-MS/FID
1 hour
0.02-0.30 ppb
PAN
GC-ECD
5 min
0.05 ppb
HCHO
Hantzsch fluorimetry
1 s
0.05 ppb
J
(O
1
D),
J
(NO
2
),
J
(HONO),
J
(NO
3
),
J
(HCHO), and
J
(H
2
O
2
)
Photolysis spectrometer
8 s
a
O
3
UV photometry
1 min
1.00 ppb
SO
2
Pulsed UV fluorescence
1 min
0.50 ppb
CO
Infrared absorption
1 min
40.00 ppb
NO
Chemiluminescence
1 min
0.50 ppb
NO
2
Chemiluminescence
1 min
0.50 ppb
a. Process-specific, 5 orders of magnitude lower than maximum at noon.
S13
Table S2.
Summary of ClNO
2
and Cl
2
peak concentrations in China (Unit: ppt).
Study Area
Observation Time
ClNO
2
Cl
2
(Peak Time)
References
Xiamen
January to February of 2023
(1 hour average)
~5600
~540 (nighttime),
~220 (daytime)
This study
Wangdu
June of 2014 (5 min average)
~3500
~450 (daytime)
13
Beijing
September of 2021 to October
of 2022
(1 hour average)
~3000
~230 (nighttime)
16
Nanjing
April of 2018 (1 min average)
~3700
~100 (nighttime)
17
Changzhou
May to June of 2019
(1 min average)
~1300
~500 (nighttime)
18
Shanghai
October to December of 2019
(1 min average)
~5700
~1100 (daytime)
18
Hong Kong
August to October of 2018
(1 min average)
~2000
~1000 (daytime)
19
Heshan
January of 2017
(1 min average)
~8100
NA
20
S14
Table S3.
Comparisons of observed parameters between during and after the Spring
Festival using the t-test. At the 0.05 level, there were significant differences in the mean
values of parameters between during and after the Spring Festival.
Parameters
During the Spring Festival
After the Spring Festival
p-value
BLH (m)
568.6 ± 420.7
457.8 ± 296.5
0.01004
T (
°C
)
13.1 ± 2.64
13.7 ± 3.75
0.25342
RH (%)
68.3 ± 19.5
57.4 ± 15.9
1.10E-08
UV (W·m
-2
)
5.95 ± 9.27
8.56 ± 12.8
4.40E-04
J
NO
2
(s
-1
)
0.00158 ± 0.00248
0.00235 ± 0.00341
1.99E-09
Cl
(μg·m
-3
)
0.344 ± 0.388
0.233 ± 0.180
4.19E-04
NO
3
(μg·m
-3
)
3.51 ± 2.00
5.43 ± 2.85
6.12E-10
NO (ppb)
0.499 ± 0.414
1.46 ± 2.94
4.40E-05
NO
2
(ppb)
3.68 ± 2.02
8.66 ± 5.10
5.20E-20
O
3
(ppb)
26.9 ± 10.1
32.3 ± 13.1
1.08E-08
PAN (ppb)
0.294 ± 0.147
0.658 ± 0.327
1.25E-29
N
2
O
5
(ppb)
0.0531 ± 0.0821
0.258 ± 0.371
5.63E-13
ClNO
2
(ppb)
0.280 ± 0.363
1.04 ± 1.20
2.24E-14
Cl
2
(ppb)
0.0269 ± 0.030
0.113 ± 0.095
3.10E-22
S15
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