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S1 /S18
ACS Earth and Space Chemistry 1
Supporting Information for 2
Evidence for strong HONO emission from fertilized agricultural fields and its remarkable 3
impact on regional O3 pollution in the summer North China Plain 4
Chaoyang Xue1, 2, #, Can Ye1, #, a, Chenglong Zhang1, 3, Valéry Catoire2, Pengfei Liu1, 3, Rongrong 5
Gu7, Jingwei Zhang6, Zhuobiao Ma1, Xiaoxi Zhao1, Wenqian Zhang5, Yangang Ren4, Gisèle 6
Krysztofiak2, Shengrui Tong5, Likun Xue7, Junling An6, Maofa Ge5, Abdelwahid Mellouki4, 7, 7
Yujing Mu1, 3* 8
1 Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 9
2 Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS–Université 10
Orléans–CNES, 45071 Orléans Cedex 2, France 11
3 Centre for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese 12
Academy of Sciences, Xiamen 361021, China 13
4 Institut de Combustion Aérothermique, Réactivité et Environnement, Centre National de la Recherche 14
Scientifique (ICARE-CNRS), Observatoire des Sciences de l’Univers en région Centre, CS 50060, 45071 15
cedex02, Orléans, France 16
5 Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China 17
6 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), 18
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, Beijing 100029, China 19
7 Environmental Research Institute, Shandong University, Qingdao, Shandong 266237, China 20
a now at: State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of 21
Environmental Sciences and Engineering, Peking University, Beijing 100871, China 22
Correspondence to: [email protected] 23
Contents of this file (18 pages) 24
Texts S1 to S6 25
Figures S1 to S7 26
Tables S1 to S3 27
References 28
29
30
S2 /S18
Text S1. 31
Instruments used in this campaign 32
At both sites, HONO was continuously measured online by Long Path Absorption Photometer 33
(LOPAP-03, QUMA GmbH, Germany). At the agricultural site, the external sampling unit for 34
ambient measurement was mounted at a height of 3.4 m above the ground. NO and NO2 were 35
measured by a chemiluminescence technique analyzer (Thermo Fisher Model 42i, USA). The 36
instrument can directly quantify NO by the reaction 𝑁𝑂 + 𝑂3 → 𝑁𝑂2∗ → 𝑁𝑂2 + ℎ𝜐 . O3 was 37
measured by a UV photometric analyzer (Thermo Scientific Model 49i, USA). H2O2 was measured 38
by a wet liquid chemistry fluorescence detector (Aero-Laser AL2021, Germany).1 Besides, the 39
meteorological parameters (air temperature, relative humidity, solar radiation, wind speed, and 40
wind direction) and soil temperature were measured by a meteorological station. Soil water content 41
was measured once every two days through the mass loss of soil samples (5 cm depth) by heating 42
for 24 hours at 105 °C.2 Soil pH was measured once every two days based on the method of ISO 43
10390:2005-2012. 44
Since NO2 was quantified indirectly through conversion to NO by a molybdenum converter with 45
possible interference from other NOy species like HONO, HNO3, and PAN, then NO2 46
concentrations used here were corrected by subtracting HONO from the measured NO2. HNO3 and 47
PAN were unfortunately not available in this campaign, which leads to an overestimation of NO2. 48
While, the overestimated NO2 may not have a significant impact on the HONO budget and the 49
following soil HONO emission flux estimation during the fertilization period, which is because 50
NO2 heterogeneous reactions were not the dominated HONO source after fertilization. For example, 51
during the intensive fertilization period (Figure S4), NO2 heterogeneous reactions only contribute 52
6% of the daytime HONO formation, much lower than the other sources (85%). Therefore, the 53
overestimation of NO2, even by a factor of 2, is still far to significantly affect the HONO budget 54
and the soil HONO emission flux estimation. Meanwhile, if HNO3 and PAN are furtherly 55
subtracted from the measured NO2, 1) HONO/NO2 will be larger so that NO2 reactions are farther 56
to explain the observed HONO/NO2, and 2) the unknown HONO strength and the estimated soil 57
HONO emission flux will be even larger, suggesting an even larger impact of fertilization on 58
daytime atmospheric oxidizing capacity. 59
At the non-agricultural site, NO, NO2, O3, and J(NO2) were continuously measured by a 60
chemiluminescence method (T-API Model T200U, USA), a Cavity Attenuated Phase Shift detector 61
(T-API Model T500U, USA), a standard UV photometric detector (TEI Model 49C, USA), and a 62
spectroradiometer (Metcon GmbH, Germany), respectively. Details about other instruments could 63
be found in Gu et al.3 64
S3 /S18
Text S2. 65
HONO levels during NFP and A6FP at the agricultural site 66
HONO levels during the non-fertilization period (NFP) at the agricultural site was needed as a 67
background level for estimation on HONO emission flux during PFP and IFP. As fertilization for 68
summer maize is a regionwide event in the NCP and may last 1-2 weeks if all the agricultural 69
fertilization is finished, we got limited observations completely without fertilization impact during 70
the present campaign. While we had measurements from 1st to 6th in August 2016 (six weeks after 71
fertilization in this year, A6FP), and we found the HONO levels were very similar to those on the 72
first day (no fertilization within 3 km around our station) of measurement in 2017. Therefore, we 73
used data on the first day to represent the levels during NFP. All these daytime HONO and the 74
calculated Punknown during NFP or A6FP, were much lower than those during IFP, suggesting that 75
the background HONO level has a small impact on estimating soil HONO emission flux. HONO 76
variations during NFP and A6FP showed a typical diurnal variation, indicating one fertilization 77
event's impact may last less than 6 weeks. 78
Text S3. 79
Photolysis frequency (J) values 80
During the campaign, solar irradiance (Ra, W m-2) was continuously measured, while J values were 81
not measured. Then we conducted a field measurement of solar irradiance and J(NO2) (10-3 s-1) by 82
a spectroradiometer (Metcon, GmbH, Germany) in June 2020 at the same place, in which the high 83
quadratic correlation of Ra and J(NO2) (J(NO2)=-9.96×10-6×Ra2+1.62×10-2×Ra, R2=0.95) is used 84
to estimate J(NO2) in June 2017. Then J(HONO) and J(O(1D)) were then calculated by the TUV 85
model (https://www2.acom.ucar.edu/) and scaled by the estimated J(NO2), as shown in the 86
following equation. 87
𝑱(𝑿) = 𝑱(𝑿)𝒎𝒐𝒅𝒆𝒍 ∗ 𝑱(𝑵𝑶𝟐)𝒆𝒔𝒕𝒊𝒎𝒂𝒕𝒆𝒅/𝑱(𝑵𝑶𝟐)𝑻𝑼𝑽 (S1) 88
where X represents HONO or O(1D). 89
Text S4. 90
Punknown calculation 91
Except for homogeneous reaction NO+OH (PNO+OH) and photo-enhanced NO2 uptake on the ground 92
surface (Phet), unknown HONO strength could be calculated by the following equation: 93
𝑷𝒖𝒏𝒌𝒏𝒐𝒘𝒏 = 𝑳𝒑𝒉𝒐 + 𝑳𝑯𝑶𝑵𝑶+𝑶𝑯 − 𝑷𝑵𝑶+𝑶𝑯 − 𝑷𝒉𝒆𝒕 94
= [𝑯𝑶𝑵𝑶] ∗ 𝑱(𝑯𝑶𝑵𝑶) + 𝒌𝟏 ∗ [𝑯𝑶𝑵𝑶] ∗ [𝑶𝑯] − 𝒌𝟐 ∗ [𝑵𝑶] ∗ [𝑶𝑯] −𝒗(𝑵𝑶𝟐)×[𝑵𝑶𝟐]
𝟒×𝑴𝑳𝑯× 𝜸𝑵𝑶𝟐
×𝑱(𝑵𝑶𝟐)
𝟓×𝟏𝟎−𝟑 𝒔−𝟏 (S2) 95
S4 /S18
where Lpho is the photolysis rate of HONO, LHONO+OH is the loss rate of HONO due to reaction with 96
OH, (NO2) is the molecular speed of NO2 (m s-1), NO2 (1.5×10-5) is the uptake coefficient of NO2 97
on the ground surface4,5, MLH is the mixing layer height (see Text S5 for detailed calculation), and 98
J(NO2) is the photolysis frequency of NO2. J(NO2)/(5×10-3 s-1) plays as the photo-enhancement 99
factor of the NO2 heterogeneous reaction. J(HONO) represents the photolysis frequency of HONO, 100
which was derived from solar irradiance measurement and the TUV model (see details in Text S2). 101
Reaction rate constants k1 and k2 were taken from IUPAC (http://iupac.pole-ether.fr/). OH 102
concentrations were estimated based on the correlation of OH with J(O(1D)) from a previous field 103
campaign at the same site in the same month, in which high correlation (R2=0.86) of OH with 104
J(O(1D)) was observed.6 105
Text S5. 106
Calculation of HONO emission flux 107
Within the mixing layer, soil HONO emission causes the increase of Punknown, and the increment of 108
Punknown is the upper limit of soil HONO emission flux (E, ng m-2 s-1) through the following equation. 109
𝑬 =(𝑷𝒖𝒏𝒌𝒏𝒐𝒘𝒏−𝑷𝑰−𝑷𝒖𝒏𝒌𝒏𝒐𝒘𝒏−𝑵)×𝑴𝑵×𝑴𝑳𝑯
𝑽𝒎×𝟑𝟔𝟎𝟎× 𝟏𝟎𝟗 (S3) 110
where Punknown-PI represents Punknown (m3 m-3 h-1) during PFP or IFP, Punknown-N, MN, and Vm represent 111
the average Punknown during NFP, nitrogen molar mass (14 g mol-1), and gas molar volume (0.0245 112
m-3 mol-1, at 101 kPa and 298K), respectively. 3600 and 109 have units of s h-1 and ng g-1, 113
respectively. 114
Regarding MLH, vertical mixing is determined by turbulence, and the vertical travel distance ∆z 115
(therefore, it is the upper limit of MLH) over time τ can be calculated by the following equation. 116
∆𝒛 = √𝟐 × 𝑲𝒛 × 𝝉 (S4) 117
where Kz and τ represent the turbulent diffusion coefficient and the photolytic lifetime of HONO, 118
respectively. For a typical Kz of 3×105 cm2 s-1, the calculated ∆z is 200 m at 13:00 when the 119
photolytic lifetime of HONO is shortest (667 s, J(HONO)=1.5×10-3 s-1) in the daytime. 120
Since MLH is expected to have the same variation as BLH, then the diurnal variation of MLH is 121
calculated based on the diurnal BLH obtained from ECMWF (https://www.ecmwf.int/) scaled by 122
the ratio of ∆z-to-BLH at 13:00. Then the BLH obtained from ECMWF, and the calculated MLH 123
are shown in Figure S5. Note that ∆z is the upper limit of MLH as gradient distribution is expected 124
to be significant when the ground-based source is dominated. Therefore, the flux inferred based on 125
the present MLH represents the upper limit of the soil HONO emission flux. But the evidence of 126
the main conclusion that the fertilized agricultural field is a strong HONO source is still sufficient. 127
S5 /S18
Text S6. 128
Net OH production 129
1. Net OH production rate from the photolysis of HONO (P(OH)HONO) 130
𝑷(𝑶𝑯)𝑯𝑶𝑵𝑶 = [𝑯𝑶𝑵𝑶] × 𝑱(𝑯𝑶𝑵𝑶) − 𝒌𝑵𝑶+𝑶𝑯 × [𝑵𝑶] × [𝑶𝑯] − 𝒌𝑯𝑶𝑵𝑶+𝑶𝑯 × [𝑯𝑶𝑵𝑶] ×131
[𝑶𝑯] (S5) 132
2. OH production rate from the photolysis O3 (P(OH)O3) 133
𝑶𝟑 + 𝒉𝝊 → 𝑶(𝟏𝑫), 𝑱(𝑶(𝟏𝑫)) (S6) 134
𝑶(𝟏𝑫) + 𝑴 → 𝑶 + 𝑴 (𝑴 = 𝑵𝟐), 𝒌𝒔𝟕 (S7) 135
𝑶(𝟏𝑫) + 𝑴 → 𝑶 + 𝑴 (𝑴 = 𝑶𝟐), 𝒌𝒔𝟖 (S8) 136
𝑶(𝟏𝑫) + 𝑯𝟐𝑶 → 𝑶𝑯 + 𝑶𝑯, 𝒌𝒔𝟗 (S9) 137
𝑷(𝑶𝑯)𝑶𝟑= [𝑶𝟑] × 𝑱(𝑶𝟑) × ∅ × 𝟐 (S10) 138
The reaction rate constants kNO+OH, kHONO+OH, ks7, ks8, and ks9 were taken from IUPAC 139
(http://iupac.pole-ether.fr/). H2O concentration could be calculated by the measured relative 140
humidity (RH), temperature, and pressure. During this campaign, the daytime average branching 141
ratio of O(1D) with H2O (∅) was 12.3%. 142
S6 /S18
Figures 143
144
Figure S1. Locations of the agricultural site (star A, 3842N, 11515E) and the non-145
agricultural site (star B, 37°46N, 118°59E) in the map colored by land type distribution 146
(from Peng et al.7). 147
S7 /S18
148
Figure S2. Time series of hourly HONO, NO2, O3, H2O2, and solar irradiance (Ra) during the 149
three periods at the agricultural site. A6FP: six weeks after the fertilization (1st-6th August 150
2016); NFP: the non-fertilization period (7th June 2017); PFP: the pre-fertilization period (8th-151
13th June 2017); IFP: the intensive fertilization period (14th-21st June 2017). 152
153
154
S8 /S18
155
156
Figure S3. Diurnal variations of NO and NO2 mixing ratios during the three periods at the 157
agricultural site. NFP: the non-fertilization period; PFP: the pre-fertilization period; IFP: 158
the intensive fertilization period. 159
160
S9 /S18
161
Figure S4. HONO formation rates and contribution from each source during the three 162
periods at the agricultural site. NFP: the non-fertilization period; PFP: the pre-fertilization 163
period; IFP: the intensive fertilization period. 164
165
S10 /S18
166
Figure S5. The BLH obtained from ECMWF and the calculated MLH 167
168
169
S11 /S18
170
171
Figure S6. Backward trajectories (12 hours) for YelRD station at 12:00 in each day during 172
IFP (obtained from NOAA HYSPLIT MODEL with GDAS meteorological data, 173
https://www.ready.noaa.gov/HYSPLIT.php). 174
175
S12 /S18
176
177
Figure S7. Pollution rose plot for the observations at the non-agricultural sites during IFP. 178
179
180
S13 /S18
Tables 181
182
Table S1. Laboratory HONO emission flux (in ng-N m-2 s-1) measurement and the key factor 183
in the literature. 184
Soil information Maximum flux Key factors Reference
1-3000a pH, nitrite 8
pH>7 5-258 AOB 2
Agricultural land and other substrates Surface acidity 9
Agricultural land, Parkland 8-19 Nitrification 10
Biocrusts 5-173 Nitrogen cycling by biocrusts 11
High water content 5-190 Nitrate reduction 12
Pure cultures of AOB, NOB, and AOA 0-800 Biogenic hydroxylamine 13
Soil surface and biocrusts ~150 Microscale pH 14
Bare soil and biocrusts 27-175 Soil cover type, nutrient contents 15
a: the calculated maximum emission 185
AOB: ammonia-oxidizing bacteria 186
Biocrusts: biological soil crusts 187
188
S14 /S18
Table S2. Field HONO emission flux (in ng-N m-2 s-1) measurement and the main 189
precursor/source in the world. 190
Date Location Land type Method Range Mean Precursor Reference
Sept, 1989 Halvergate, UK Grassland AG -12-25 3.2 NO2 16
Feb-May, 1990 Essex U, UK Grassland AG -24-33 -6.6 NO2 16
May-June, 1998 Milan, Italy Grassland AG -20-8 -0.2 NO2 17
July-Aug, 2008 Michigan, USA Forestland REA -24-61 0.4* nitrate 18
July, 2009 Blodgett, USA Forestland REA -24-33 -0.1* 19
May-June, 2010 Bakersfield, USA Agricultural
land REA -14-24 0.7* NO2
19
June-July, 2011 Bavaria, Germany Clearing land AG 0.1-1.0 0.6 NO2 20
Sept, 2012 Bavaria, Germany Forestland AG -0.2-0 -0.1* 20
Aug, 2009 Grignon, France Agricultural
land AG 0.1-2.3 1.2* NO2
21
Apr, 2010 Grignon, France Agricultural
land AG -0.1-0.2 0.1* NO2
21
Aug, 2011 Grignon, France Agricultural
land AG 0.1-2.3 1.2* NO2
21
Aug, 2015 Wangdu, China Agricultural
land OTC 0.6-3.2 1.9 NO2
22
Aug, 2015 Wangdu, China Fertilized
agricultural land
OTC 5.7-40 21 Emission 22
*: the average of diurnal maximum and minimum 191
AG: aerodynamic gradient 192
REA: relaxed eddy accumulation 193
OTC: open-top dynamic chambers 194
195
196
S15 /S18
Table S3. The statistical summary of daytime (6:00-18:00) HONO, NO2, HONO/NO2, O3, 197
H2O2, P(OH)HONO, P(OH)O3, and solar radiation (Ra) at the agricultural site during the four 198
periods. Ave, SD, Min, and Max represent the average, standard deviation, minimum, and 199
maximum, respectively. A6FP: six weeks after fertilization; NFP: the non-fertilization 200
period; PFP: the pre-fertilization period; IFP: the intensive fertilization period. 201
Parameters HONO
(ppbv)
NO2
(ppbv)
HONO/NO2
(%)
O3
(ppbv)
H2O2
(ppbv)
P(OH)HONO
(ppbv h-1)
P(OH)O3
(ppbv h-1)
Ra
(W m-2)
A6FP
Ave 0.23 12.1 2.1 40 - 0.24 0.37 346
SD 0.20 7.1 1.2 22 - 0.20 0.36 208
Min 0.03 3.7 0.5 3 - -0.20 0 29
Max 1.14 37 6.0 77 - 0.89 1.18 731
NFP
Ave 0.36 13.3 2.6 50 0.66 0.78 0.52 471
SD 0.26 7.6 1.0 25 0.55 0.53 0.44 234
Min 0.05 5.4 0.5 9 * 0.07 0.01 97
Max 0.86 25.6 4.5 79 1.41 1.65 1.14 757
PFP
Ave 0.72 16.1 5.4 53 0.60 1.49 0.45 381
SD 0.32 8.1 3.7 30 0.52 1.15 0.43 232
Min 0.17 4.1 1.5 1 * -0.15 0 10
Max 1.49 40.5 21.8 106 1.80 4.23 1.49 764
IFP
Ave 1.36 14.4 11.8 70 0.95 3.02 0.66 391
SD 0.60 7.9 8.0 32 0.72 2.08 0.60 226
Min 0.40 5.6 3.1 5 * -0.12 0 0
Max 3.13 39.5 37.6 122 2.59 10.69 1.90 737
-: measurement was unavailable. 202
*: H2O2 mixing ratios were lower than the detection limit of about 0.1 ppbv. 203
Note that noontime H2O2 on 17th June was not considered because of a possible impact from a 204
vegetation fire accident. 205
206
S16 /S18
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