Environmental Science & Technology Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Energy Golden Triangle, Northwest China
Yanjie Shen, Xiaodong Zhang, Jeffrey Robert Brook, Tao Huang, Yuan Zhao, Hong Gao, and Jianmin Ma
Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.6b00182 • Publication Date (Web): 07 Jun 2016 Downloaded from http://pubs.acs.org on June 7, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Satellite Remote Sensing Of Air Quality In The Energy Golden Triangle In 1
Northwest China 2
Yanjie Shen1, Xiaodong Zhang1, Jeffrey R. Brook2, Tao Huang1, Yuan Zhao1，Hong 3
Gao1*, Jianmin Ma1,3*
4
Affiliation:
5
1Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, 6
College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, 7
China 8
2Air Quality Research Division, Atmospheric Science and Technology Directorate, 9
Environment Canada, 4905 Dufferin St., Toronto, Ontario, Canada M3H 5T4 10
3CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China 11
12
*Corresponding author: Jianmin Ma, Hong Gao 13
Tel: +86 15293166921, fax: +86-931-8911843, email: [email protected]； 14
Word account: 2632; Figures: 3 16
Abstract 17
This article presents the first assessment of air quality in the Energy Golden Triangle 18
(EGT) in northwest China. Using the planetary boundary layer (PBL) column density 19
(PCD) of SO2 and the tropospheric column density (TCD) of NO2 retrieved from the 20
Ozone Monitoring Instrument (OMI), we show that the column densities of both SO2
21
and NO2 exhibit an increasing trend from 2005 to 2014 in the Ningdong energy and 22
chemical industrial base (NECIB) within the EGT，in contrast to the rapid and 23
widespread decrease of SO2 emissions in northern China. This is largely attributed to 24
the rapid development of the energy industry in this region. It is expected that SO2
25
and NO2 emitted from the EGT would increasingly contribute to the totalemissions of 26
these two air pollutants in northern China.
27 28 29 30 31 32 33
TOC Art 34
35
1. Introduction 36
Fossil fuel industries are major sources of air pollutants,1 Due to rapid 37
industrialization and urbanization over the past decades, the increasing demands for 38
energy supply in China have imposed serious adverse effects on air quality，
39
particularly in northern China where most of the heavy industry is located. Under the 40
national strategy for energy development and safety during the 21st century, oil, 41
natural gas, coal mining industries，and thermal power generators have been relocated 42
towards energy-abundant northwest China,2,3 Consequently, the Energy Golden 43
Triangle (EGT), which is located in this region (Figure S1 of Supporting Information, 44
SI), is now the largest new energy and chemical industry base in China providing 25%
45
of the country’s energy production,4 The total fossil fuel resources in the EGT are 46
equivalent to 2 trillion tons of standard coal and account for approximately 40% of the 47
country's total. In particular, the Ningdong energy and chemical industrial base 48
(NECIB) in the Ningxia Hui Autonomous Region,5 a sub-region in the EGT (Figure 49
S1), is a nationally prioritized region for the promotion of the development of 50
large-scale coal mining bases, thermal power generation, and the chemical industry.
51
To guarantee national energy security and to promote the regional economy，the EGT 52
energy program has been accelerating since 2010 reaching the national goals for coal 53
production of 1.45×109 tons, oil output of 5.4×107 tons, and natural gas production of 54
5.5×1010 m3 in 2015.4 ,6Given the low annual precipitation ranging from 100 mm to 55
400 mm and sparse vegetation coverage,7,8 the poor ecological environments in the 56
EGT region are uniquely susceptible to atmospheric pollution. It is hypothesized that 57
the increased release of pollutants to the air, water and land that is associated with 58
rapid development in the EGT will have a considerable impact on the local 59
environment. These effects can also be expected to extend to the downstream regions 60
in eastern China via atmospheric transport and river flows. In particular, the EGT 61
region is located in the upper reaches of the Yellow River, the second largest river in 62
China, which passes through the EGT and has been the main source of water supply 63
not only to local industries, but also to a vast region of eastern and central China.
64
Knowledge of the magnitude and extent of the environmental contamination and 65
impact associated with EGT development is very limited. No detailed air quality 66
monitoring data are available and the limited local government reports and air quality 67
assessments indicate that air quality in the EGT has been improving over the past 68
decade. These assessments state that levels of most criteria air pollutants were well 69
below the national standard.5,9 Here we attempt to independently assess the air quality 70
in the NECIB and EGT using satellite remote sensing data to quantify the influence of 71
the rapid development in the EGT on the local environment since 2005. Through the 72
use of satellite-based observations, it is possible to obtain valuable information on 73
emissions, spatial-temporal patterns, and annual trends of many air contaminants10-12. 74
In particular, air quality remote sensing with relatively high spatial resolution has 75
been improved rapidly in the last several years. Notably, the Ozone Monitoring 76
Instrument (OMI) on the NASA EOS Aura platform provides daily global coverage in 77
combination with small ground pixel sizes (nominally 13 × 24 km2 at nadir, 78
minimum 13 × 12 km2 at nadir),12-15 and the Infrared Atmospheric Sounding 79
Interferometer.15,16 This article presents the satellite retrieved column densities of 80
sulfur dioxide (SO2) and nitrogen dioxide (NO2) as well as their trends from 2005 to 81
2014 over the EGT and NECIB with a high spatial resolution, aiming to fill critical 82
knowledge gaps and understand air quality in the EGT given the shifting energy base 83
in northern China. Awareness of the implications of these large scale national policies 84
are important for assessing and minimizing impacts.
85
2. Materials and Methods 86
The OMI-derived PCD ( DU) of SO2 and TCD (1015 molec cm-2) of NO2 with a fine 87
spatial and temporal resolution were collected from the NASA EOS and KNMI 88
(Koninklijk Nederlands Meteorologisch Instituut), respectively.15,18 The operational 89
OMI PBL data are processed using the highly sensitive band residual difference (BRD) 90
algorithm to facilitate the acquisition of information on near-surface SO2 emission16. 91
The NO2 vertical column densities are obtained using a differential optical absorption 92
spectroscopy (DOAS) algorithm that converts NO2 slant column densities to vertical 93
columns.19,20 The SO2 PCD and NO2 TCD have been validated against their respective 94
monitored air concentrations in northern China.14,20 In the present study, the 95
OMI-retrieved column densities of SO2 and NO2 have been compared with the 96
available daily and monthly ambient air concentration data of these two chemicals at 97
official air quality monitoring stations and in the China National Environmental 98
Monitoring Center (http://106.37.208.233:20035/) near the central NECIB region.
99
Details of the comparisons are presented in the SI (text and Figures S2 and S3).
100
Two emission inventories for SO2 and NOx (nitrogen dioxide, NOx=NO+NO2 101
where NO is nitric oxide) are available in China. The first one covers East Asia with 102
gridded emission data before 2006.21 The other provides gridded SO2 and NOx 103
emission data from four emission sectors (industry, residential, power generation, and 104
transportation) for every two years from 2008 to 2012.22 Figures S4 and S5 display 105
the SO2 and NOx annual emissions from different emission sectors in 2008, 2010, and 106
2012,22 averaged over the NECIB and over a selected region of northern China (see 107
below for description of this region).
108
3. Results and Discussion 109
3.1 OMI-retrieved SO2 and NO2 in EGT and NECIB 110
Figure 1 shows the spatial distribution of SO2 PCD and NO2 TCD over the EGT and 111
four bordering provinces (inner map), averaged over 2005-2014 at a 0.25°×0.25°
112
latitude/longitude resolution. Higher SO2 PCDs (Figure 1a) and NO2 TCDs (Figure 113
1b) can clearly be observed in Ningdong (Yinchuan), Erdos, and the north of Yulin 114
(also seeing Figure S1). The higher 2005-2014 mean SO2 PCD and NO2 TCD extend 115
from the central NECIB region to Shizuishan in Ningxia and Wuhai in Inner 116
Mongolia. Wuhai and Shizuishan are traditional coal mining areas in northwest China.
117
The energy industries in these two regions have rapidly expanded since the early 118
2000s to provide raw coal to the Ningdong chemical and thermal power industries.
119
Due to SO2 emissions from coal mining industry, the daily ambient air 120
concentrations of SO2 in Wuhai were considerably higher than in Yinchuan (Figure 121
S6a). Conversely there were relatively higher levels of NO2 over Yinchuan compared 122
to Wuhai (Figure S6b), which was likely due to the larger number of motor vehicles 123
in Yinchuan (population 2.1 million) compared with that in Wuhai (population 0.56 124
million).
125
Since the coal mining and power generation industries in the NECIB sub-area 126
of the EGT have been experiencing the fastest expansion in recent several years, we 127
compared the monthly mean PCD of SO2,averaged over the NECIB with northern 128
China (Figure 2a, the NECIB and northern China are marked in Figure S1), where 129
air pollution levels, especially fine particulate matter (PM2.5), have received 130
significant international attention during the past three decades. Here we include in 131
northern China two mega cities (Beijing, Tianjin) and three provinces ( Liaoning, 132
Shangdong, and Hebei), which make up one of China's most populated and 133
industrialized regions. This region will be referred to as the northern China region 134
hereafter. Result from 2005 to 2014 shown in Figure 2a indicate that the SO2 PCDs in 135
the northern China region were much higher than those in the NECIB before 2011.
136
However, since 2011, the monthly SO2 PCDs over the NECIB have been similar to 137
and higher than the northern China region in magnitude. This is attributed to 138
decreasing SO2 emissions in the northern China region and increasing emissions in 139
the NECIB. The strong decline of SO2 emission from power generation after 2006 in 140
the northern China region (Figure S4c) was a result of regulations to reduce SO2
141
emission in this region,21,22 including application of flue-gas desulfurization, and the 142
relocation of oil and coal mining industries as well as thermal power generations to 143
northwest China.23,24 144
The 2005-2014 mean SO2 PCDs and NO2 TCDs are generally consistent with the 145
mean SO2 and NOx emissions over 2008, 2010, and 201222 in the same region, as 146
shown in Figure 2b, c and Figure S7. The annual SO2 emissions from different 147
emission sectors averaged over the NECIB and the northern China region are 148
illustrated in Figure S4. Although the emissions from the residential and 149
transportation sectors in the northern China region were considerably higher than 150
those averaged over the NECIB in the later 2000s because of much higher population 151
density in the northern China region (Figure S4b and d), the emissions from these 152
two sectors accounted for less than 10% of the total SO2 emission. In contrast to the 153
continuously declining SO2 emission in the northern China region, for the major 154
emission sectors of industry and power generation (Figures 2a, b and Figure S4a, c), 155
the SO2 emissions averaged over the NECIB increased after 2006 and became much 156
higher than the domain-averaged emissions from power plants over the northern 157
China region, in line with the SO2 PCD changes, as illustrated in Figure 2a and b. As 158
a result, the domain-averaged total SO2 emission over the NECIB has exceeded the 159
mean emission averaged over the northern China region in 2012 (Figure 2b and S4e).
160
Similarly, the domain-averaged NOx emissions from power generation in the NECIB 161
increased rapidly and was 2.2 times higher than the emissions averaged over the 162
northern China region in 2012 (Figure 2c and S5). Although the mean NOx emissions 163
in the NECIB from the other three emission sectors were still lower than those 164
averaged over the northern China region, the total NOx emission from all emissions 165
sectors in the NECIB increased more rapidly than those averaged over the northern 166
China region due to markedly increasing NOx emission from power generation in the 167
NECIB (Figure S5e).
168
Figure S8a and b further compare the annual emissions of SO2 and NOx from 169
power generation21 with annually averaged column densities of SO2 and NO2
170
retrieved from OMI over the EGT in 2008, 2010, and 2012, showing agreement 171
between the emissions and column densities of SO2 and NO2. Knowing that the 172
thermal power industry contributed primarily to the NECIB and EGT development6, 173
the association between SO2 and NOx emission patterns and the column densities of 174
these two criteria air pollutants confirmed that the coal mining and thermal power 175
industry in this region likely played a significant role worsening local air quality.
176
3.2 Trends of OMI-retrieved column densities of SO2 and NO2
177
Table S1 presents the non-parametric Mann-Kendall statistical test (Z)25 and Sen’s 178
estimated slopes (Q)26 for the monthly mean SO2 PCD and NO2 TCD in the NECIB, 179
EGT, and the northern China region. The statistically significant declining trend of 180
SO2 PCD in the northern China region is indicated by the negative Z value (-6.698, 181
p<0.01) for the time series of the monthly mean SO2 PCDs, in line with its linear 182
trend in this region (Figure 2a). The SO2 PCD in the EGT also exhibits a decreasing 183
trend, characterized by the negative Z value of -3.62 (p<0.01) and the negative linear 184
trend (slope=-0.0002, R2=0.089, p=0.0009). While the positive Z value (1.626) and 185
the slope of the linear trend (slope=0.0002, R2=0.022, p=0.1013, Figure 2a) of the 186
monthly mean SO2 PCD in the NECIB suggests an increasing trend, , these positive 187
trends are not statistically significant using the p<0.05 and |Z|>Z1-α/2=1.96 criteria 188
(Table S1). Accordingly, Sen's slope Q revealed the faster decreasing rate of the 189
monthly SO2 PCD time series in the northern China region (-0.0019) as compared 190
with that in the EGT (-0.0002), whereas a positive Sen's slope Q for the SO2 PCD 191
(0.0002) was estimated in the NECIB.
192
Figure 3a shows the gridded trends of the annual mean SO2 PCDs (DU) from 193
2005 to 2014 across the four provinces (Figure 1 inner map) where the EGT is 194
located. These trends were estimated from the linear regression of SO2 PCDs against 195
the time sequence from 2005 to 2014 for each grid square. Overall the SO2 PCDs 196
exhibited negative trends in the EGT. We would expect the decline of SO2 emissions 197
in the EGT from 2012 onward. Conversely, as shown in Figures 2a and 3a, the SO2 198
PCDs increased in the NECIB during 2005-2014, in agreement with the increasing 199
SO2 emissions in this sub-region in the EGT (Figures 2b and S4), particularly from 200
power generation and industry. The increasing SO2 emission in the NECIB can also 201
offset the declining emission over the EGT.
202
Figure 3b illustrates the spatial pattern in the trend of SO2 PCDs for the same 203
period but for the EGT only. The positive trend of SO2 PCDs can now be more clearly 204
seen to only be over the NECIB，in contrast to the decline of SO2 emissions in the 205
northern China region and other EGT regions. Among the three areas in the EGT, 206
intensive coal and oil mining in Yulin and Ordos was initiated in the early 1990s and 207
has slowed down considerably since 2008 partly due to decreasing demands to raw 208
coal in China,27 whereas the energy industry in the NECIB has been accelerating since 209
the mid-2000s under strong support from provincial and central governments28 to 210
provide electric power to eastern China. These geographic patterns in socioeconomic 211
change are clearly reflected in the PCD values (Figure 3b). Compared with SO2, the 212
NO2 TCDs over the NECIB did not exhibit a declining trend after 2008 (Figure S3).
213
The measured annual mean NO2 air concentrations in Yinchuan (40 km west of the 214
NECIB) decreased from 2005 to 2008 and increased thereafter, showing an overall 215
increasing trend, somewhat consistent with NO2 column densities. This is attributable 216
to more difficulties in the control of NO2 emissions from industry, power generation, 217
and transportation. Differing from the SO2 measurements (Figure S6a), Figure S6b 218
shows the relatively higher NO2 levels in Yinchuan than in Wuhai in most cases, 219
which is likely due to the proximity of Yinchuan to the NECIB and more motor 220
vehicles in Yinchuan.
221
Following the shift of energy industries, fossil fuel mining, and chemical 222
industries to northwest China and stricter emission control regulations in the 223
traditional industrialized regions in China, significant emission reductions are 224
reported for the northern China region and these are being reflected in the observed 225
vertical column densities of SO2. It is anticipated that such reductions will continue in 226
the coming years. In localized areas of the EGT/NECIB, where emission activities 227
have been expanding, there have been modest increases in SO2, particularly since 228
2010. As a national energy base for the 21st century, the development of the 229
EGT/NECIB also is projected to continue for many years. Considering the potentially 230
fragile ecological environments in this area, the impact in the EGT (NECIB) due to 231
degraded air quality and higher levels of related contaminants on a range of 232
environmental media needs to be carefully monitored. More investigations are 233
required to fill knowledge gaps in the emissions of toxic chemicals, greenhouse gases, 234
and the responses of eco-sensitive environments in order to minimize future impacts.
235
ASSOCIATED CONTENT 236
Supporting Information. Additional material as noted in the text. This material is 237
available free of charge via t http://pubs.acs.org.
238
ACKNOWLEDGMENTS 239
This work is supported by the National Natural Science Foundation of China through 240
grants 41371478 and 41371453. We acknowledge the free use of SO2 PBL column 241
density and tropospheric NO2 column density data from OMI，and SO2 and NOx
242
emission data from Multi-resolution Emission Inventory for China (MEIC). We thank 243
Dr. S. Venkatesh for his helpful comments and edits to the manuscript.
244
References:
245
(1). Kampa, M.; Castanas, E. Human health effects of air pollution. Environ. Pollut.
246
2008, 151, 362-367.
247
(2). Zhu, J.; Ruth, M. Relocation or reallocation: Impacts of differentiated energy 248
saving regulation on manufacturing industries in China
.
Ecological Economics.249
2015, 110, 119-133.
250
(3). Dorian, J. P.;Abbasovich, U. T.; Tonkopy, M.S.; Jumabekovich, O. A.; Qiu, 251
Daxiong. Energy in central Asia and northwest China: major trends and 252
opportunities for regional cooperation. Energy Policy. 1999, 27, 281-297.
253
(4). Zhang, J.; Yu, Z.; Li, Q.; Liu, J. Forecasting and analysis for coal productivity in 254
the Energy Golden Triangle. Coal Engineering. 2013, 11, 782-785, in Chinese.
255
(5). Chang, R.; Li, F. Prediction and study of atmospheric pollutant concentration in 256
Ningdong based on multiple polymerization process neural network. J. Guizhou 257
Normal Uni. ( Natural Sciences). 2012, 30, 98-102, in Chinese.
258
(6). Li, T. Emerging of Energy Golden Triangle. J. Chinese. Oil Mag. 2011, 8, 20-23, 259
in Chinese.
260
(7). Li, Y.; Wang, D.; Zhang, M. Analysis of water resources demand and guaranteed 261
supply measures of Golden Triangle Energy in MSGN region. Water Resour.
262
Power. 2012, 30, 35-37, in Chinese.
263
(8). Gu, D. Water resource protection and utilization engineering technology of coal 264
mining in “Energy Golden Triangle” region. Coal Engineering. 2014, 46, 33-37, 265
in Chinese.
266
(9). Han, Y.; Gao, J.; Li, H; Li, Y. Ecological suitability analysis on the industry 267
overall arrangement plan of Ningdong energy sources and chemical industry 268
base. Environ. Sci. Manager. 2007, 32, 142-147, in Chinese.
269
(10). Edwards, D.P. Air quality remote sensing from space. Eos Transactions 270
American Geophysical Union. 2006, 87, 327-327.
271
(11). Martin, R. Satellite remote sensing of surface air quality. Atmos. Environ. 2008, 272
42, 7823-7842.
273
(12). McLinden, C. A.; Fioletov, V.; Krotkov, N. A.;, Li, C.; Boersma, K. F.; Adams C. 274
A decade of change in NO2 and SO2 over the Canadian oil sands as seen from 275
space. Environ. Sci. Technol. 2016, 50, 331-337.
276
(13). Balis, D.; Kroon, M.; Koukouli, M. E.; Brinksma, E. J.; Labow, G.; Veefkind, J.
277
P.; McPeters R. D. Validation of Ozone Monitoring Instrument total ozone 278
column measurements using Brewer and Dobson spectrophotometer 279
ground-based observations, J. Geophys. Res., 2007, 112, D24, S46.
280
(14). Krotkov, N. A.; Mcclure, B.; Dickerson, R. R.; Carn, S. A.; Li, C.; Bhartia, P. K.;
281
Yang, K.; Krueger, A. J.; Li, Z.; Levelt, P. F.; Chen, H.; et al. Validation of SO2 282
retrievals from the ozone monitoring instrument over NE China. J. Geophys.
283
Res. Atmos. 2008, 113, D16, 259-269.
284
(15).Plate, M. B. T.; Aisma, F.; Vries, J. D.; Oord, G. H. V. D. Ozone monitoring 285
instrument: system description and test results. Proc Spie. 2001, 4540, 122-134.
286
(16). Fioletov, V. E.; McLinden, C. A.; Krotkov, N.; Yang, K.; Loyola, D. G.; Valks, P.;
287
Theys, N.; Van Roozendael, M.; Nowlan, C.; Chance, K. et al. Application of 288
OMI, SCIAMACHY and GOME-2 satellite SO2 retrievals for detection of large 289
emission sources. J. Geophys. Res. Atmos. 2013, 118, 399-418.
290
(17). Boynard, A.; Clerbaux, C.; Clarisse, L.; Safieddine, S.; Pommier, M.; Van 291
Damme, M.; Bauduin, S.; Oudot, C.; Hadji-Lazaro, J.; Hurtmans, D; Coheur, 292
P-F. First simultaneous space measurements of atmospheric pollutants in the 293
boundary layer from IASI: A case study in the North China Plain. Geophy. Res.
294
Lett. 2014, 41, 645-651.
295
(18). Carn, S. A.; Krueger, A. J.; Krotkov, N. A.; Yang, K.; Levelt, P. F. Sulfur dioxide 296
emissions from peruvian copper smelters detected by the ozone monitoring 297
instrument. Geophy. Res. Lett. 2007, 34, 1093-1101.
298
(19). Russell, A. R.； Perring. A.；Valin, L. C.; Bucsela, E. J.; Browne, E. C.; Min, K.
299
E.; Wooldridge, P. J.; Cohen, R. C. A high spatial resolution retrieval of NO2 300
column densities from OMI: method and evaluation. Atmos. Chem. Phys. 2011, 301
11, 8543-8554.
302
(20). Cai, Z.; Liu, Y.; Wang, P.; Meng, X.; Xia, J. Preliminary comparison of OMI 303
PBL SO2 data to in-situ measurements in Beijing. Society of Photo-Optical 304
Instrumentation Engineers (SPIE) Conference Series . Society of Photo-Optical 305
Instrumentation Engineers (SPIE) Conference Series. 2008, 7152.
306
(21). Lu, Z.; Streets, D. G.; Zhang, Q.; Wang, S.; Carmichael, G.R.; Cheng, Y. F.;
307
Wei, C.; Chin, M.; Diehl, T.; Tan, Q. Sulfur dioxide emissions in China and 308
sulfur trends in East Asia since 2000. Atmos. Chem. Phys. 2010,10, 6311-6331 309
(22). Li, M.: Zhang, Q.; Kurokawa, J.; Woo, J. H.; He, K. B.; Lu, U.; Ohara, T.; Song, 310
Y.; Streets, D. G.; Carmichael, Y. R. et al. MIX: a mosaic Asian anthropogenic 311
emission inventory for the MICS-Asia and the HTAP projects, Atmos. Chem.
312
Phys. Discuss. 2015, 15, 34813-34869.
313
(23). Mu, F.; Zhong, W.; Zhao, X.; Che, C.; Chen, Y.; Zhu, J., Wang, B. Strategies for 314
the development of CBM gas industry in China. Natural Gas Industry B. 2015, 315
2, 383-389.
316
(24). Chen, J.; Cheng, S.; Song, M.; Wang, J. Interregional differences of coal carbon 317
dioxide emissions in China. Energy Policy. 2016, 96, 1-13.
318
(25). Kendall, M. G. Rank Correlation Methods. 4th ed., 202 pp, Charles Griffin, 319
London, 1975.
320
(26). Sen, P. K. J. Estimates of the regression coefficient based on Kendall's tau. Am.
321
Stat. Assoc. 1968, 63, 1379-1389.
322
(27). U.S. Energy Information Administration (EIA). Independent Statistics and 323
Analysis-China.2014.http://thegenerator.com.au/u-s-energy-information-adminis 324
tration-eia-independent-statistics-and-analysis-2/ (accessed June 3 2016).
325
(28). Lin, X. Speed up of the development of Ningdong energy and chemical industrial 326
base in Ningxia. Petro-Chem. Equip. 2004, 5, 31-32, in Chinese.
327
Figure captions 328
Figure 1. OMI-retrieved column densities of SO2 and NO2 averaged from 2005 to 329
2014 in the EGT and four bordering provinces (Inner Mongolia, Shaanxi, Ningxia, 330
and Gansu) at the spatial resolution of 0.25o×0.25o lat/lon. (a) Gridded annual mean 331
SO2 PBL column density (DU), and (b) NO2 tropospheric column density (1015 molec 332
cm-2). The EGT is encircled by Ordos, Yulin, NECIB, and includes their respective 333
extended areas (coal mine, power generators, and chemical industry). The inner map 334
on the up-left corner highlights the location of the four bordering provinces of the 335
EGT relative to all of China.
336
Figure 2. (a) Monthly mean OMI SO2 PBL column density (DU) from 2005-2014 337
averaged over the northern China region (the one of China's economic engine) and the 338
NECIB (Figure S1). Blue and red dashed lines in Figure 2a represent linear trend of 339
SO2 PCDs in the NECIB (slope=0.0002, R2=0.022, p=0.1013) and the northern China 340
region (slope=-0.002, R2=0.328, p=0.0003), respectively; (b) annual mean SO2 PCD 341
and its emissions (ton yr-1) over the NECIB in 2008, 2010, and 2012; (c) annual mean 342
NO2 TCD and NOx emissions (ton yr-1) over the NECIB in 2008, 2010, and 2012.
343
Figure 3. Linear trends (slopes) of OMI retrieved SO2 PCD (DU) across (a) 4 344
provinces (Inner Mongolia, Shaanxi, Ningxia, and Gansu as shown in Figure 1), and 345
(b) EGT.
346 347
348
Figure 1 349
350
Figure 2.
351
352
Figure 3 353
. 354