Sulfur Dioxide Emissions from Combustion in China - ACS Publications

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Sulfur Dioxide Emissions from Combustion in China: From 1990 to 2007 Shenshen Su, Bengang Li,* Siyu Cui, and Shu Tao College of Urban and Environmental Sciences, MOE Laboratory for Earth Surface Processes, Peking University, Beijing 100871, People's Republic of China

bS Supporting Information ABSTRACT: China has become the world’s largest emitter of SO2 since 2005, and aggressive deployment of flue gas desulfurization (FGD) at coal-fired power plants appeared in China when facing the formidable pressure of environment pollution. In this work, we estimate the annual emission from combustion sources at provincial levels in China from 1990 to 2007, with updated data investigations. We have implemented the method of transportation matrix to gain a better understanding of sulfur content of coal in consuming provinces, which in turn improved the inventory. The total emissions from combustion in 2007 were 28.3 Tg, half of which was contributed by coal-fired power plants. Meanwhile, the industrial boiler coal combustion and residential coal consumed in centralized heating were responsible for another 32% of the total emissions. From 1990 to 2007, annual SO2 emission was fluctuated with two peaks (1996 and 2006), and total emission doubled from 15.4 Tg to 30.8 Tg, at an annual growth rate of 4.4% (6.3% since 2000). Due to the extensive application of FGD technology and the phase-out of small, high emitting units, the SO2 emission began to decrease after 2006. Furthermore, the differences among estimates reported in literatures highlight a great need for further research to reduce the uncertainties with more detailed information on key sources and actual operation of devices.

’ INTRODUCTION Sulfur dioxide (SO2) is one of the most important air pollutants. As the precursor gas to sulfate aerosol, SO2 contributes to acid deposition, visibility degradation, and climate change, besides its adverse effect on the increase of morbidity. Sulfate aerosol can be transported long distances from Asia to North America, therefore SO2 can affect the environment not only locally, but also on a global scale.1
5 Following the dramatic increase of the economy growth and energy use, the SO2 emission of China have changed remarkably during the last period, and the emission growth and associated impacts on local heath, long-range transport, as well as climate change are getting more and more attention.6 Among the air pollution control policies aimed at reducing the SO2 emission in China, the most important one is 10% reduction compared to the SO2 emission level in 2000 during the Chinese 10th (2001
2005) and 11th (2006
2010) Five-Year Plan period, respectively, which was made by the Ministry of Environmental Protection (MEP). While failing to achieve the goal in the former period, China had hit the emission reduction target ahead of schedule. Because the emission inventory is the first input to the transport, deposition, and climate modeling studies, it is important that the emission must be accurately estimated and can reflect the spatial pattern of sources. The SO2 emissions in China have been reported by many studies. At the beginning of the 1990s, the SO2 emissions from China were estimated based on r 2011 American Chemical Society

fuel consumption, sulfur content in fuels, and emission factors in the original work to develop Asian or global inventories.7
10 Later studies made efforts in methodology improvement through using representative emission factors and sulfur contents, which varied greatly between regions and influenced the estimation significantly. Researchers such as Streets et al. studied the Asian emissions in a comprehensive and consistent way for the first time at that period, and Ohara et al. developed regional-specific emission factors from a wide range of sources.11,12 Emission inventory has enjoyed further improvement since control measures like flue gas desulfurization (FGD) came into consideration to reflect the spread of desulfurization devices in China.13
15 Meanwhile, some researchers developed an improved technologybased methodology at the unit level with detailed operation data in plants, in order to reflect the types of technology presently operating in China.14,15 With this improved method, Lu et al. first presented the change of SO2 emission in China since 2000 based on the dynamic technology penetration.16 As the FGD devices were installed at an unprecedented annual rate, while there were no guarantees that the installed FGD equipment was running continuously before 2007, the actual operation of FGD systems Received: May 16, 2011 Accepted: August 18, 2011 Revised: August 1, 2011 Published: August 18, 2011 8403

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Figure 1. Inventory domain included in this work. The color of gray represents the sulfur content of coal produced by each province. The pie demonstrates the percentage of coal consumption with different sulfur content, and the region without pies provides needed coal all by itself.

at coal-fired power plants had been widely discussed. Field measurements, data investigations and informative interviews were conducted to reduce the uncertainty of FGD operation in the emission inventory studies.17
19 In this work, we provide a feasible and accessible method with updated energy consumption, regional-specific sulfur content of coal consumed and emission control performance at provincial level, to estimate the annual SO2 emissions from 1990 to 2007, that consequently will lead to improved inventory which in turn serves models and regulators. The specific objectives of this study were (1) to derive the sulfur content of coal as burned by province through the method of transportation matrix among provinces; (2) to update the activity rates and relative parameters to improve the inventory; (3) to construct the emission factor database for some fixed sources based on the public data in literatures that concerned China particularly; and (4) to give a clear picture on the change of SO2 emission in China historical emissions between 1990 and 2007 to serve models and also regulators.

’ DATA AND METHODOLOGY The target domain of this study covered 34 regions which are shown in Figure 1 (including 23 provinces, 5 autonomous districts, 4 municipalities, Hong Kong, Macao, and Taiwan). The general methodology based on energy consumption and emission factors was widely used in the development of emission estimations, and the total emission of a region or nation is the sum of emissions from each fuel sector.8,11,12 The SO2 emission at provincial level was calculated using eq 1. Eni ¼

∑j ∑k Anijk EFnijk

ð1Þ

where subscripts i, j, k, n represent province, sector, fuel type (or subsector) and year, respectively; A stands for the activity rates, such as fuel consumption; EF is net emission factor, and for coal

combustion sources, it can be calculated with the following equation: EFnij_coal ¼ 2  Snij  ð1
SrÞ  ð1
Rnij Þ

ð2Þ

where Snij is the sulfur content of coal used in year n, province i, sector j; Sr is the sulfur retention in ash; Rnij is the removal rate of emission control measures. Data. In this work, we estimated the emissions from combustion of five sectors, apart from the most common four sectors (power generation, industry, transportation and residential), the open biomass burning was included.13,20 Each sector contained several subsector sources based on the different types of fuel combusted. Since the energy consumption data of China can be obtained from China Energy Statistics Yearbook (CESY) by National Bureau of Statistics (NBS) and International Energy Agency (IEA) reports, both were used in the estimation of emission.8,12,16 According to the comparison between the two kinds of statistics, the total energy consumption based on province-by-province data from NBS were higher than that from IEA statistics since the IEA statistics were mainly based on the national data, and did not contain the local use of coal and oil covered by the provincial statistics.21,22 Therefore, province-byprovince data from NBS was adopted in this work. Detailed data collection of fuel consumption is presented in section Emission Activities. Emission Activities. The emission sources included in this study are shown in Table 1. The coal, oil, and gas consumption in different sectors at provincial level was collected from China Energy Statistics Yearbook (1990
2007).23 Residential crop residues and firewood consumption of provincial level from 1990 to 2007 was collected from published official yearbooks.23 Agriculture waste burning was estimated based on the method by Cao, using the production of 10 types of crops from 1990 to 2007, production-to-residue ratio of crop specified, and the percentage of residues burned outdoor was included.24 The 8404

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Table 1. Fifteen SO2 Emission Sources Included in This Work, and Emission Factors for Individual Sources (g kg
1) emission sector

subsector sources

factor

household coal (urban and rural) coal consumed in centralized heating

1.98a 10.7c

crop residues burning

0.35a

firewood burning

0.09a

liquid petroleum gas/natural gas (LPG/NG)

0.15a

boiler coal combustion

10.7c

oil combustion

3.78a

gas combustion

0.15a

power plants

coal combustion oil combustion

10.9c 11.10a

transportation

motor vehicle diesel consumption

5.83a

motor vehicle gasoline consumption

2.50a

agriculture waste burning in the field

0.22a

forest fire

0.99b

grass fire

0.35b

residential

industrial

open biomass burning

a

Log-normal distribution for individual emission sources, and presented as geometric mean. Detailed statistics and distribution information are listed in Supporting Information SI2. b Lacking adequate EFs in sources of forest fire and grass fire, particular log-normal distribution were assumed. Detailed statistics and distribution information are listed in Supporting Information SI2. c Average of provincial emission factors for 2007, which were derived through eqs 2 and 3. Detailed methods and results are listed in Supporting Information SI1.

provincial data of forest and grass fire from 1990 to 2007 was from the study of Yuan.25 As the emission estimation from coal combustion was the most pivotal step mentioned above, a number of related materials were used in this study. The removal rate of emission control technologies applied in boiler coal combustion of power and industry sector was derived from the ratio of removed to total emitted SO2 reported by MEP of each province from 1990 to 2007, respectively.26,27 The ratio was used to represent the combined effect of actual emission abasement rate, which depended on the efficiency, implementation rate and operation condition of abatement measures.17 And the sulfur retention in ash of the power and industry sector was derived based on some specific plants data with least-squares method (Table S1 of the Supporting Information, SI). It is worth mentioning that the distribution of coal resource in China is very uneven, leading to a fact that the coal consumed in a province is usually from many other provinces with varied sulfur content.28 The actual sulfur content for consuming provinces was derived through the method of transportation matrix with eq 3, based on the composition of coal consumption in each province derived from the transportation and sale volume among provinces,29 and sulfur content in each supplying province, which was represented by the average of sulfur contents in different coal mines within the province (data from 260 coal mines in China). 30 Sc ¼ MSr

ð3Þ

where Sc is the sulfur content of coal in consuming provinces; M is the transportation matrix, and a particular element mpq in the matrix means the percentage of coal from province q consumed

in province p; Sr is the sulfur content of coal resources in supplying provinces. The result is presented in Figure 1, and detailed data of removal efficiency, sulfur retention in ash and sulfur content on retrieving the Emission factors of coal are presented in Figure S1, Table S1, and Table S2. Since detailed sulfur contents and abatement technology information of Hong Kong, Macao and Taiwan were not typically available in the governmental yearbooks, the sulfur content of coal consumed in Hong Kong and Macao was assumed the same with that of Guangdong province, and the national average sulfur content was used to represent that of Taiwan. The highest FGD application rate of the other 31 mainland provinces was assumed to present that of Hong Kong, Macao, and Taiwan.11,12,17 Emission Factor. For some coal combustion sources, namely coal consumed in power plants, industry and centralized heating, the EFs were derived through eqs 2 and 3. As the coal production of Shanxi province and other important provinces was relatively stable during the study period, while that of Inner Mongol grew dramatically after 2003, which consequently affected the coal production pattern significantly (Figures S2 and S3 of the SI). Inner Mongol even became the largest coal producer instead of Shanxi in 2010. Therefore, several assumptions were adopted in deriving the sulfur content, such as (1) before 2002 (1990
2002), the sulfur content of coal in consuming provinces was assumed fixed and chosen from several Chinese literatures;31
33 (2) after 2004 (2004
2007), transportation matrix was introduced to derive the sulfur content in each year;29 (3) and that of 2003 was derived through linear interpolation (average of 2002 and 2004) due to data limitation. Referring to other sources included in our inventory, a comprehensive EFs database was developed through collecting data from a detailed literature review. In order to represent the emission of China more accurately, only the data measured in China or other similar developing countries in Asia was adopted by the database, except for sources of open biomass burning sector. Some of the EFs of a specific source reported in the literature varied by orders of magnitude, and if log-normal distribution was detected, geometric mean of EFs for individual emission sources was used to estimate the emission. The value of each source adopted in this work is shown in Table 1, and detailed statistics and literature information are listed in the Table S3 and Figure S4 of the SI.

’ RESULTS AND DISCUSSION Current SO2 Emission from Combustion in China. The total annual SO2 emission from combustion in China was estimated 28.3 Tg in 2007, and the contribution of power stations, industry, residential, transportation, and open biomass burning were 14.64, 10.08, 2.40, 1.13, and 0.06 Tg, respectively. In terms of fuel-type contribution, 26.38, 1.67, 0.10, 0.17 Tg could be allocated to coal, oil, gas, and biomass combustion respectively. The total Chinese SO2 emission from combustion in this work (30.5 Tg in 2005 and 30.8 Tg in 2006) was lower than those reported by Klimont et al. (34.4 Tg in 2005), Lu et al. (32.3 Tg in 2007), Smith et al. (32.7 Tg in 2005), Zhao et al. (30.7 Tg in 2005) and Zhang et al. (31.0 Tg in 2006),12
16,34 but higher than the results of China MEP (24.7 Tg in 2007).26 Among the various sources, power station coal consumption ranked first as the largest emitter (50.7%), followed by industrial boiler coal combustion (34.5%) and residential coal consumed in 8405

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Figure 2. Relative contributions of various sources to total SO2 emission in China in 2007. Open biomass burning contains three sources, namely, agriculture waste burning in the field, forest fire, and grass fire; other contains crop residues, firewood burning, liquid petroleum gas/natural gas (LPG/ NG) in residential sector and industrial gas combustion.

centralized heating (6.9%). The sum of the SO2 emissions from these three sources accounted for 92.1% of the total emission. Detailed information on the contribution of each source to total Chinese SO2 emission from combustion in 2007 is demonstrated in Figure 2. Since coal-fired power plant has been considered as the most important source in energy saving and emission mitigation, the Chinese government has taken multiple measures to control the emissions from this source, e.g., all new thermal power units as well as most existing ones (with sulfur content higher than 0.7%) were required to be installed with FGD system; small units with low energy efficiency were gradually shut down in the past few years.17,18 The percentage of unit installed with FGD was at least 60.3% in 2008, and has reached 80% in 2010,35,36 and the geometric growth of FGD application rates kept the emissions from increasing at the speed of coal consumption, especially after 2000.37 Nevertheless, the uncertainty of emissions from power station could increase as the actual operation of FGD system was unknown. The likelihood that installed FGD systems actually operate increased greatly due to the novel policy incentives in 2007 and the installation of continuous emission monitoring systems (CEMS) and a harsh penalty measure if the FGD systems do not function normally.17,18 In addition, with the development of SO2 satellite retrievals, the FGD operation could be monitored by observing the column SO2 with the help of the Ozone Monitoring Instrument (OMI) aboard NASA’s Aura satellite.38
40 For the industrial sector, because of the excluding emissions from the production process, the emissions estimated in our work are lower than that of Lu et al. (13.0 Tg, 40.2%, 2007).16 Of the emissions from industrial sector, the coal-fired source contributed the most (96.9%). SO2 emissions from residential sector were largely from coal consumed in centralized heating, which accounted for 81.2% of the total and would increase with the promotion of energy saving and emission reduction tide.41 For the transportation sector, the diesel vehicle source and gasoline vehicle source contribute 890.7 kt, 78.8%, and 239.4 kt, 21.2%, respectively. As referred to the open biomass burning, it is a very small part compared to the other sources (agriculture wastes combustion, forest fire, and savanna fire contribute 0.2% altogether). The pattern of SO2 source distribution in China was compared to that of other countries reported in literature, and the result is presented in Figure 3. The pattern of China differed considerably

Figure 3. Comparison of SO2 emission inventories with other countries (Gg y
1). Note: data presented in the figure are from emissions in 2005.

from those of India and some developed countries reported by EDGAR, such as Japan, United States, and average of OECD European countries in 2005.42,43 Namely, the contribution of power station (51.0%) was much lower than those of United States (81.5%) and OECD Europe (64.0%). The main differences seem to be the inclusion of heat production in the power section in the methodology used by EDGAR.42 While the share of industry (37.8%) was much higher than those of United States (14.2%) and OECD Europe (27.1%). Compared with Asian developed country, the contribution of transportation in Japan (18.5%) was five times more than that of China (2.9%). Finally, the share from residential in China (8.1%) was higher than those of all the other countries, which might be contributed to the inclusion of source of coal consumed in centralized heating. Comparison with Other Estimates of Chinese Emissions. On the basis of the province-by-province sulfur content, the removal efficiency of emission control technology and other related materials, SO2 emission from combustion of each province from 1990 to 2007 was calculated. Another calculation with the same conditions, except for the province-by-province sulfur contents replaced by national average sulfur contents was conducted as well. The results of the two calculations were compared to the official statistics reported by the China MEP (2001
2007),26 and the comparisons are demonstrated in Figure 4. Compared with the estimations using the weighted-average national sulfur content, the improvement by using province-byprovince sulfur content is significant. 8406

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Figure 4. Comparison of the SO2 emissions derived from provincial level and statistics of the yearbook, 2001
2007 (emissions from the production process were subtracted), and Hong Kong, Macao, and Taiwan were not included. Case 1: calculation based on province-by-province sulfur contents; Case 2: calculation base on weighted-average national sulfur contents.

Because Chinese coal resources are spatially heterogeneous, and the distribution pattern is reverse compared to that of economic development (Shanxi, Inner Mongol, and the other four intern provinces hold 81.6% of Chinese coal available reserves, while Shanghai, Beijing, Zhejiang, and the other 11 coastal developed provinces hold only 5.3% of the total).44 Besides, the sulfur content vary markedly at provincial level.10,44 Therefore, the accuracy of SO2 emissions in China is generally estimated at the level of 10% or even more.10,34 Through the method of the transportation matrix, the source/consumer relationship for coal based on transportation and sale volume between provinces were considered to figure out the actual sulfur contents for coal consumed in each province. For example, as shown in Figure 1, the sulfur content of coal consumed in Heilongjiang Province was 0.36%, while that of Guizhou Province was 1.79%, since the national average sulfur content was 1.01% (2007) according to our estimates, if the national average sulfur content were used, then the emissions of each province would be overestimated and underestimated, respectively. Therefore, the provincial estimates showed better agreement with those of China MEP, which matched much closer to the 1
1 line, compared with those estimated from weighted-average national sulfur content. Note that most of the provincial estimates in our study are higher than corresponding results published by the MEP of China (from 2001 to 2007), especially for those provinces with large emissions, such as Jiangsu, Shandong and Henan provinces. There is the same issue with previous studies, and the differences may be caused by the inconsistent of the coal consumption in Province-by-Province data and that of CESY.12,45 While neglecting the open biomass burning, firewood, and residential straw sources in the China MEP Yearbooks only contribute a tiny part, since the emissions from these are rather small. 11,15,16 Therefore, a further comparison of the activities rates and methodology between the inventories in literatures and official estimations is needed. Table 2 compares the Chinese emissions in 2005, 2006, and 2007 by sector according to this study and other inventories. For

total SO2 emissions, the values from our estimates agree well with most of the other inventories, and the differences might be smaller if the emissions from industrial process were covered in this work. Since the use of higher sulfur content (1.15% vs 1.02% in this study) and lower sulfur retention in ash (10% vs 14% in this study) might offset the underestimation caused by the adoption of IEA energy statistics, emissions estimated by Smith et al. coincide well with those of the others.34 The underestimate of emissions by Zhao et al. might be due to the application of EFs from a foreign database and the power plant information from MEP, which only covers large units.14 As the fuel consumption values in power plants from IEA are almost the same as those of CESY, the reason for the inconsistency in this sector might be the difference of other parameters used in each inventory. 15,16 Namely, the average coal EF of INTEX-B (15.4 g/kg) is higher than those of Lu et al. and this work; the average FGD penetration estimated by Lu et al. is 9%, 22%, and 40% for 2005, 2006, and 2007 (the corresponding EF is about 15.0, 13.2, and 11.0 g/kg), while the removal efficiency in this study is 18%, 26%, and 42% (the corresponding EF is 14.6, 13.0, and 10.9 g/kg), respectively.16 What’s more, the emissions from the source of heat production were calculated in the residential sector in this work, not power plant sectors as other inventories, which leads to relatively lower values in this work as well. For the industrial sector, the values in the estimations with CESY energy data (Lu et al., INTEX-B and this work) are higher than those of estimates with IEA or others.13,42 The value in GAINS is much lower than others because a lower sulfur content (0.998%), a higher sulfur retention in ash (25%), and a much lower EF (about half of the power plants EF) was used in the inventory. For SO2 emissions from residential sources, the data are in good agreement with each other. And the emissions from transportation in this work agree well with those of EDGAR, but are much higher than the values reported by Lu et al. and Zhang et al. The probable reason is the differences in EF used in each estimation.15,16 Temporal Trend of SO2 Emissions in China. On the basis of the activity data, emission factors and relative parameters 8407

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Table 2. Estimates of Annual SO2 Emission in China by Sector after 2005 (Gg) studies

methoda

sourcesb

REc

IN

PO

TR

BB

total

Smith et al.,2005

BU

FF + BF + BB + NI

GAINS,Klimont,2005

BU

FF + BF + NI

2058

5616

19392

46

32673

EDGAR v4.1,2005

BU

FF + BF + BBd

2331

9010

22534

724

Zhao et al.,2005

BU-TB

FF + BF + BB + NI

Lu et al.,2005

BU-TB

FF + NI

18400

Lu et al.,2006

BU-TB

FF + NI

18600

Lu et al.,2007

BU-TB

FF + NI

2737

13000

16428

158

32323

INTEX-B,Zhang,2006 this work, 2005

BU-TB BU

FF + BF + NI FF + BF + BB

2838 2471

9725 11505

18333 15548

123 889

52

31020 30466

this work, 2006

BU

FF + BF + BB

2521

10973

16180

1016

62

30751

this work, 2007

BU

FF + BF + BB

2404

10087

14641

1130

57

28319

27113 7

34607 30700 32300 33200

a

BU = bottom-up mass balance approach, by fuel and sector; BU-TB = bottom-up technology-based at unit level. b FF = fossil fuel; BF = biofuel combustion; BB = open biomass burning; NI = noncombustion industrial process. c RE = residential; IN = industrial; PO = power plants; TR = transportation. d Source categories of Industrial Processes and Product Use are not counted in the Industrial sector.

Figure 5. Temporal trend of combustion emissions for SO2 in China (left), and sectoral contributions between 1990 and 2007 (right). Note: EDGAR data presented in the left figure exclude the emissions from industrial process.

described in section Data and Methodology, SO2 emissions from combustion in China were calculated for the period 1990
2007 and the annual variations of total emissions and the distributions of each sector during the study years are presented in Figure 5. From 1990 to 2007, the total emission fluctuated with two peaks in 1996 and around 2006, respectively. The total SO2 emission from combustion in China increased monotonically before 1996, as the energy consumption increased with the condition of Chinese GDP hitting 10.5
14.2% from 1992 to 1995.46 But influenced by the Asian economic crisis, the emissions decreased subsequently until 2000. After 2000, the SO2 emissions rose remarkably until around 2006 with high elasticity ratio of energy consumption, especially for 2002
2004 (ratio > 1),47,48 which means the dramatic change was influenced greatly by the economic boom. Those emissions increased from 15.3 to 28.3 Tg (1.9 times) during the period 1990
2007. The annual SO2 emissions calculated in this work were examined along with previous estimates including those estimated by the MEP, and the results are demonstrated in Figure 5(left).10,12,13,15,16 A year by year comparison between the REAS inventory and this work

between 1990 and 2003 shows that the growth trends of the two inventories compare well. Since the industrial processes were not included in this study, the estimates are lower than those of REAS at each year. However, the difference between the inventories is much larger after 2000 than before, which might be due to not reflecting the recent spread of FGD in China.49 The variation in this study after 2000 is in good agreement with the inventory developed by Lu et al., and the under estimation in 2005 to 2007 might be attributed to inconsistency in applied abatement technologies, a factor that became essential for the accuracy of emission estimates recently.16 Among the various estimations, EDGAR covers almost the same sources concerned in this study, and our emissions coincide with those of EDGAR from 1996 to 2003.42 As almost all of the estimates in this work are higher than those of MEP, which is the same issue confronted by the previous work. The differences would be attributed to the differences in activity rates, or methodologies, or particular parameters in each inventory. Therefore, more detailed information on sulfur content, removal efficiencies are needed to reduce the uncertainties. The estimated SO2 emission from every sources of 34 regions in 8408

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Environmental Science & Technology China of 5-year intervals (1990, 1995, 2000, 2005, 2007) are listed in Tables S4
S8 of the SI. In terms of contribution by each sector in China (Figure 5, right), the contribution of power plants increases from 35.6% in 1990 to 53.8% in 2002. Additionally, with more and more FGD facilities applied in power plants and phasing out of small, highemitting units, an overall declining trend was seen since 2002.16,26,37 It is well-known that the capacity of coal-fired power plants with FGD devices grew remarkably before 2007, especially during each of 2006 and 2007, over 100 GWe capacity was installed (larger than the total capacity with FGD in United States, 99 GWe). The issue of actual operation of FGD systems attracted much attention since China MEP announced that only a small part (less than 40%) of FGD devices were running reliably. However, the hurdle of high operation and maintenance costs seemed to be overcome by the novel policy with two significant provisions in 2007, then the FGD devices were largely operating as they were supposed to do. 17,18 The effectiveness of the FGD devices in reducing SO2 emission was confirmed by the dramatic reductions observed by OMI from 2007 to 2008, while before 2007 substantial increase in total column SO2 was observed.40 As the number of units without FGD devices will become less and less in the future, which restricting the potential for further emission cuts, Chinese government reduced the goal of SO2 emission abasement to 8% in the twelfth five year plan (compared to 10% in the eleventh five year plan).50 The contribution of industry sector varies greatly from 56.2% to 35.6% due to the energy saving action plan of 1000 enterprises and the shutting down of captive power plants with capacity under 50 000 kw. The contribution of the residential sector generally increases from 6.5% in 1990 to 8.5% in 2007. The increase seems mainly to be attributed to the energy consumption growth following rapid urbanization, which outweighed the effect of fast development of centralized heating systems in large cities. While the effect of replacing coal stoves with liquid petroleum gas/natural gas stoves might be ignored as well. Although the vehicle emission standard become more and more strict, SO2 emission from motor vehicles still increase to a certain extent (increased by 5 times from 0.23 to 1.13Tg) owing to significant growth in vehicle numbers, especially in Beijing, Yangtze River Delta and Pearl River Delta, which contribute remarkably to the urban air pollution.51
53 The contribution of open biomass burning is rather small and kept stable during the study period (less than 1%). Opposite to a relatively weak seasonal change of China’s emission, the seasonal variation of this sector is relatively strong, as SO2 emissions from source of agriculture waste burning in the field peak after the crop harvest and forest and grass fire happened frequently from February to May every year.11,15

’ ASSOCIATED CONTENT

bS

Supporting Information. Additional data, analysis, tables, and figures: Figure S1, Provincial removal efficiency in 2006 and 2007; Table S1, Derivation of Sulfur retention in ash; Figure S2, The annual coal production of Shanxi and Inner Mongol; Figure S3, The coal production pattern of China at provincial level in 1990, 1996, 2002, and 2006; Table S2, Composition of coal consumption in each province in 2007; Table S3, Statistics of EF of each emission source; Figure S4, Distributions of the reported EFs for each source; Tables S4
S8, Emissions by sections of each province in 1990, 1995, 2000, 2005, and 2007.

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This material is available free of charge via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Phone and fax: +86-10-62758502. E-mail: [email protected].

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