Biomass burning injects many different gases and aerosols into the atmosphere
that could have a harmful effect on air quality, climate, and human health.
In this study, a comprehensive biomass burning emission inventory including
domestic and in-field straw burning, firewood burning, livestock excrement
burning, and forest and grassland fires is presented, which was developed for
mainland China in 2012 based on county-level activity data, satellite data,
and updated source-specific emission factors (EFs). The emission inventory
within a 1
Biomass burning is considered a significant source of gas and particulate
matter (PM), resulting in a major impact on atmospheric chemistry, climate,
and human health. Active trace gases (e.g. sulfur dioxide (SO
Prior to its rapid economic development, China was a large agricultural country and thus once consumed a large amount of biofuels (e.g. straw and firewood). With the dramatic urbanization that accompanied economic development, the pattern of energy consumption in rural areas has been gradually transformed. In particular, in some agricultural areas with relatively high income, straws were more frequently burned in the field (Sun et al., 2016). Since 1999, the Chinese government has issued a series of laws and regulations to ban the in-field burning of straw and to encourage comprehensive utilization of straw, such as returning it to the field and using it in livestock feeding, industrial raw materials manufacturing, briquette fuel processing, etc. (MEP, 1999). However, the effect of this legislation was not satisfactory because the processes of comprehensive straw utilization not only required high labour costs but also delayed sowing the next crop. Thus, the phenomenon of straw in-field burning continued to occur. The amount of in-field straw burning in China in 2009 was estimated at 0.215 billion Mg. These data were obtained from the governmental report on the investigation and evaluation of crop straw resources in various provinces in China (MA, 2011). Accordingly, a comprehensive and detailed emission inventory of biomass burning representing the current status in China is important to provide valuable information for researchers and policymakers. Examples of potential applications include research to understand the influence of biomass burning on indoor air quality and the outdoor atmospheric environment, and the development of effective management decisions to relieve the associated environmental burden and to reduce health risk.
Since the early research conducted by Crutzen et al. (1979), a series of efforts have been made to develop biomass burning emission inventories, especially in developed countries (Reddy and Venkataraman, 2002; Ito and Penner, 2004; van der Werf et al., 2006; Nelson et al., 2012; Shon, 2015). Compared with the developed countries, research by Chinese scientists on this issue started relatively late. The initial studies on biomass burning emission inventory across China (Streets et al., 2001, 2003; Tian et al., 2002; Cao et al., 2005) or in certain regions (Zheng et al., 2009; Huang et al., 2011) were developed mainly based on EFs developed for foreign nations (Turn et al., 1997; Andreae and Merlet, 2001; US EPA, 2002) because of the lack of local measurements in China. However, this approach could introduce great relative uncertainty in emission estimates because of the differences in crop types and combustion conditions between China and other counties.
In recent years, various research activities have focused on the emission
characteristics of biomass burning in China, including local EF and chemical
species profile tests. Li et al. (2007a, 2009) conducted field measurements
to determine the EF for several of the main household biofuels in Beijing,
Chongqing, Henan, and Shandong. Li et al. (2007b) determined the EF for
in-field wheat and maize straw burning and Cao et al. (2008) measured EFs for
the domestic burning of rice straw, wheat straw, corn straw, and cotton
straw. Zhang et al. (2008) measured CO
Based on the local EFs, emission inventories that focused on certain
provinces (Li et al., 2015; He et al., 2015) or city group regions (He et
al., 2011; Fu et al., 2013) were developed. In our previous study, we
reported an emission inventory with high resolution in the
Beijing–Tianjin–Hebei region of China (Zhou et al., 2015). To produce a
national emission inventory, several studies of biomass burning have been
carried out without distinguishing the detailed crop straws (Lu et al., 2011;
Yan et al., 2006; Tian et al., 2011). Moreover, there are several studies
that have focused on certain pollutants (Huang et al., 2012c; Chen et al.,
2013; W. Zhang et al., 2013; Kang et al., 2016; Li et al., 2016) and on
certain crop straws (Zhang et al., 2008; Hong et al., 2016; Sun et al.,
2016). In recent years, the comprehensive biomass emission inventory has been
limited. Most recent studies have concentrated on biomass open burning,
including the multi-year trend analysis on certain or multiple pollutants
(Wang and Zhang, 2008; Song et al., 2009; Shi and Yamaguchi, 2014; Shon, 2015; Xu et
al., 2016; Zhang et al., 2016). Few studies have covered recent firewood
burning (see next paragraph for details regarding the reason for this). In
addition to the EF, detailed activity data are also important for a reliable
emission inventory, such as domestic and in-field straw burning percentages,
which are not currently publicly available. Gao et al. (2002) produced a
study on the percentage of straw used as fuel and for direct incineration in
2000. Wang et al. (2008) investigated the percentage of in-field straw
burning in six regions in China in 2006, which were divided according to
their similarities in agriculture, climate, economy, and region. Tian et al. (2011)
estimated the proportion of domestic and in-field straw burning in 2007 for
seven and three regions of China, respectively. Thus, there is limited
information about the percentage of straw used as fuel or waste in the field
that reflects the status of China in recent years for different provinces.
Moreover, because of the lack of a firewood consumption report in the
Consequently, we have identified several weaknesses in the current biomass
burning emission inventories. First, not all biomass burning sources have
been included in recent years, especially since 2008, because of the lack of
firewood consumption data in the various statistical yearbooks (e.g. the
In this study, a comprehensive biomass burning emission inventory including
domestic and in-field straw burning, firewood and livestock excrement
burning, and forest and grassland fires was developed for the Chinese
mainland (excluding Hong Kong, Macao, and Taiwan) for 2012, based on detailed
activity data and satellite burned-area data. In addition, we attempted to
take the source-specific EFs measured in China into full account. A range of
important information for estimating emissions (e.g. province-specific
domestic/in-field straw burning percentage, detailed firewood burning
quantities, and uneven temporal distribution coefficient) were obtained from
a field investigation, systematic combing of latest research, and regression
analysis of statistical data. A 1 km-resolution emission inventory was
generated using GIS software. The gaseous and particulate pollutants examined
in this research included SO
Classification of biomass burning emission sources.
The remainder of this paper is structured as follows. In Sect. 2, we describe
the methodology, including the emission estimation method, the selection and
handling of activity data and corresponding parameters, determination of EFs,
spatial and temporal allocation, and speciation of PM
The biomass burning considered in this study is mainly divided into two categories, domestic burning and open burning. Domestic burning mainly involves domestic straw (straw burned as fuel indoors), firewood, and livestock excrement (mainly used in pastoral and semi-pastoral areas) burning. Open burning includes in-field straw burning (straw burned as waste outdoors, including crop stalk and residue) and forest and grassland fires. Straw burning without a specific description in this paper refers to the total straw burning, including in-field and domestic straw burning. Details of the source classifications are shown in Table 1.
A bottom-up approach was used to develop the biomass burning emission
inventory for all districts or counties. The annual biomass burning emissions
(
The burning mass of domestic and in-field straw burning can be calculated
using Eq. (2) as follows:
Domestic and in-field straw burning percentage of each province.
There are currently no statistics on the amount of each crop yield at the
county resolution (
The variable
Regression analysis between firewood consumption at province resolution and (1) rural population, (2) gross agricultural output, and (3) timber yield denoted by circles, crosses, and triangles, respectively. Regression equations for each figure are provided in the top, middle, and bottom panels.
The
Straw-to-product ratio (
Firewood consumption is recorded as non-commodity energy in the
Forest and grassland biomass fuel loadings in each province.
The burning mass of forest/grassland can be calculated from the annual mass
of forest/grassland burned (Mg year
Burned-area data for 2012 were derived from the Moderate Resolution Imaging
Spectroradiometer (MODIS) direct-broadcast burned-area product (MCD64A1;
Earlier research on the estimation of fuel loading (FL) values for forest and grassland typically employed an averaged value of above-ground biomass density. However, these values do not reflect the spatial variations of FL for each vegetation type well. In this study, numerous local FL values were collected for each province and vegetation type. The type of vegetation burned in each pixel was determined by the 1 km-resolution MODIS Land Cover product produced by Ran et al. (2010). We considered 10 vegetation types as forest and grassland (i.e. evergreen needleleaf forest, evergreen broadleaf forest, deciduous needleleaf forest, deciduous broadleaf forest, mixed forest, closed shrublands, open shrublands, woody savannas, savannas, and grassland). The FL values employed in this study are listed in Table 4. As for the combustion factor (CF), it has usually been set as a constant in previous literature. In our paper, CF values were collected for each vegetation type, and the CF in each pixel was determined by the MODIS Land Cover product and the CF values of specific vegetation. The CFs of forest, closed shrublands, open shrublands, woody savannas, and grassland were set as 0.25, 0.5, 0.85, 0.4, and 0.95, respectively (Michel et al., 2005; Kasischke et al., 2000; Hurst et al., 1994).
Emission factors used in the estimation of domestic biomass burning emissions.
Note that lowercase letters indicate the data source.
Sources are from the following:
Emission factors used in the estimation of open biomass burning emissions.
Note that lowercase letters indicate the data
source. Sources are from the following:
The mass of biomass burned by animal waste was calculated using Eq. (4) as
follows:
The
In order to ensure the accuracy of the emission inventory as much as possible, it is important to choose the appropriate EF. The EFs used in this study were mainly based on localized measurements. When selecting the EFs, we applied the following principles: first, for a certain type of biomass source or crop type, we prioritized the use of EFs from localized measurements in the literature. Second, for the biomass sources or crop types which lacked localized measurements, we prioritized results from developing foreign countries similar to China above those of developed countries. Third, when localized measurement data of a certain crop type were missing, the average value of the mainstream literature in the foreign country was used as an estimate. After an extensive literature review, the resultant EFs of domestic and open burning for each pollutant and source were summarized and are presented in Tables 5 and 6, respectively.
Contributions of different sources to total biomass burning emissions in China in 2012.
In order to obtain the detailed spatial distribution characteristics of
biomass burning emissions, and to provide grid-based data for the air-quality
model simulation, the biomass burning inventory in this study was assigned
into 1
According to the temporal resolution of MODIS fire count data (MOD14/MYD14), the monthly/daily emission of in-field straw burning can be estimated based on the number of specific fire points, and the monthly/daily emission of forest and grassland fires can be calculated by the Julian day emission of forest and grassland fires. For domestic biomass source, the monthly emission of each source can be estimated based on the monthly uneven coefficient derived from our survey questionnaire. Details of the survey questionnaire are presented in the Supplement (Sect. S3). The daily domestic emission is equally allocated from the monthly emission.
Detailed speciation of NMVOC and PM
In this study, the species emission was mainly estimated based on the total
emission, and the NMVOC and PM
Biomass burning emission inventory in the 31 provinces or municipalities of China in 2012.
The annual emissions of biomass burning in mainland China are presented in
Table 7. The total annual emissions of SO
Contributions of 12 crop straw types for various pollutants in China in 2012.
In addition to the sources mentioned above, the contribution of livestock
excrement burning and of forest and grassland fires is relatively small. It
is mainly due to the small amount of biomass consumption. The biomass fuel
consumptions of these three biomass sources are 10 614, 6647, and 505 Gg,
respectively, which are significantly lower than that of domestic straw
burning (201 582 Gg), in-field straw burning (147 178 Gg), and firewood
burning (127 250 Gg). The contributions of livestock excrement burning to
PM
As mentioned in Sect. 3.1.1, straw burning is the most important biomass
burning source with considerable influence on the pollutants that most
strongly impact air quality, climate, and human health. Therefore, the
contribution of major crop straw types was analysed. Figure 3 shows the
contributions of 12 different crop straw types for various pollutants in 2012
for mainland China. Figure 3c indicates that corn, rice, and wheat straw are
the major crop straws burned as fuel and as waste in China. The contribution
is more than 80 % of the total straw burning emissions of all pollutants
studied in this paper. Corn, rice, and wheat are the major three food crops
in China with a large planting area (the output of these three kinds of grain
accounts for 70 % of the total grain output in China; NBSC, 2013c),
resulting in a large amount of straw production. Among the various crops,
corn straw burning has the largest contribution to all of the pollutants
except for CH
Contributions of different biomass sources to the emission
in each province (Gg). Note that numbers 1–12 represent the pollutants of SO
The total biomass burning emissions in 31 provinces in 2012 are presented in
Table 7. These results indicate that Heilongjiang, Shandong, Henan, Hubei,
Anhui, Sichuan, Jilin, Inner Mongolia, Hunan, and Jiangsu provinces are the
major contributors, with the total emission contributions ranging from 53 to
65 % for various pollutants. The province with the highest contribution to total
emissions of NO
The emission of detailed biomass sources of each province is presented in Fig. 4. The provinces with major contributions to total pollutant emissions for each biomass source are various. Straw burning emissions are mainly distributed in Shandong, Henan, Heilongjiang, Hebei, Anhui, Sichuan, Jilin, and Hunan provinces. The total contribution of these provinces to various pollutants is more than 58 %. This is due to the large amount of cultivated land in the northern plain region, as cultivated land in this region prioritizes economic crops that produce rich straw resources. Several regions in which firewood produces large emissions are Hunan, Yunnan, Hubei, Hebei, Sichuan, Guangdong, Shaanxi, Liaoning, and Jiangxi provinces. More than 54 % of firewood burning emissions is contributed by these provinces. These areas are mainly distributed in southern China, a mountainous region in which the forest cover is greater than 30 % (NBSC, 2013c). Livestock excrement burning emissions are mainly distributed in Tibet, Inner Mongolia, Gansu, Xinjiang, and Qinghai provinces, since livestock manure is burned as fuel only in pastoral and semi-pastoral areas in China. Emissions from forest and grassland fires are mainly distributed in Tibet, Yunnan, Heilongjiang, Xinjiang, Inner Mongolia, and Sichuan provinces, owing to the high vegetation cover and climatic conditions in these areas.
Contributions of different crop straw types to the
emission in each province (Gg). Note that numbers 1–12 represent the pollutants of SO
The contribution of biomass sources to total emissions in each province is also distinct. Straw burning has a large contribution to various pollutant emissions in Heilongjiang (79–97 %), Ningxia (87–98 %), Shandong (74–95 %), Jilin (74–95 %), Henan (61–93 %), Anhui (51–91 %), and Shanxi (61–90 %) provinces. The economic income of the rural areas in these provinces is relatively low. A large amount of straw is consumed as the main non-commodity source of energy. In addition, firewood resources are scarce in these areas and, as a result, the usage of straw is very high. Figure 4 also indicates that, for most provinces (e.g. Beijing, Tianjin, and Hebei), the contribution of domestic straw burning is greater than that of in-field straw burning. This is mainly attributable to the gradual response to the prohibition of burning straw and to the introduction of straw resource utilization measures. The emission contribution of in-field straw burning is higher than that of domestic straw burning in Hebei, Heilongjiang, and Anhui provinces. This suggests that measures undertaken to prohibit the burning of straw in these provinces still need to be strengthened. Several regions in which firewood burning produces a large component of total emissions of various pollutants are Beijing (47–90 %), Guangdong (31–83 %), Yunan (31–79 %), Fujian (30–81 %), Hainan (26–77 %), and Guizhou (27–74 %) provinces. The quantity of straw in the rural areas of these provinces is relatively low. Firewood is the main non-commodity energy used by rural people. It is worth noting that although the biomass fuel consumption in Beijing is small, compared to the straw burning emission contribution (9–41 %), firewood burning emission (47–90 %) represents a large proportion of the total biomass burning in Beijing. This is mainly due to the severe restriction of in-field straw burning. Firewood has gradually replaced straw as the main non-commodity biomass energy source in suburban Beijing in recent years (Wang, 2010; Liu, 2012). In addition, Tibet and Inner Mongolia are the major provinces where livestock excrement produces a large component of total pollutant emissions. Less crop straw and little firewood is used as a fuel source and thus livestock excrement makes a large contribution to total biomass emissions in these provinces. Forest and grassland fires have a small contribution to pollutant emissions in each province. The contribution of Hg emission by forest fires in Inner Mongolia, Sichuan, Yunnan, Qinghai, Tibet, and Xinjiang provinces is considerable (exceeding 10 %) and mainly due to the high EF of Hg for forest fires.
Biomass emission inventory at county resolution and
intensity (PM
As the largest biomass source, crop straw burning represents a major contribution to the total emissions from biomass burning. The 12 different types of straw burning emission of each province were further analysed and the results are presented in Fig. 5. The corn straw burning emission is concentrated in Heilongjiang, Shandong, Inner Mongolia, Hebei, Henan, Shanxi, and Sichuan provinces, with the total contribution reaching more than 72 %. Wheat crop straw emissions are mainly distributed in Henan, Shandong, Anhui, Hebei, Jiangsu, Sichuan, Shaanxi, Hubei, and Shanxi provinces. More than 89 % of the wheat crop straw burning emission is contributed by these provinces. Rice crop straw burning emissions are mainly distributed in Heilongjiang, Hunan, Jiangsu, Sichuan, Anhui, Hubei, Guangxi, Guangdong, and Zhejiang provinces, with the total contribution amounting to more than 71 %. Water conditions, light, and heat are better for the cultivation of rice in southern China, while low temperature, long sunshine duration, and the large temperature difference between day and night are suitable for wheat growing in northern China. In addition, soya bean, cotton, sugar cane, potato, peanut, and rape straw have a small contribution to the various pollutants, and these straws are mainly distributed in Heilongjiang, Xinjiang, Guangxi, Sichuan, Henan, and Sichuan provinces, respectively.
Gridded distribution of PM
At county resolution, we found that the spatial distributions of emissions
for various pollutants are similar, and we thus took PM
Figure 6b shows the PM
PM
Monthly variation of different biomass sources emission for each pollutant.
As the pollutants all showed a similar emission distribution, PM
Monthly variation of different biomass sources emission
for PM
Figure 8 shows the monthly emission of all 12 pollutants considered,
indicating that there are different monthly emission variations for each
pollutant. The pollutants showing large monthly variations were SO
Burning activity mainly occurs in the harvest season (in-field straw burning)
or crop-sowing season (clearing the cultivated land and increasing the soil
fertility for the next sowing), and it varies by burning habit in different
regions. In addition, the sowing and harvest seasons vary in different
regions because of climatic conditions. Because of the differences in burning
activity and climatic conditions in various regions, monthly emission
features vary regionally, so to consider this, we divided China into
seven areas, again taking PM
Uncertainty ranges of different pollutants in emission estimates (min, max). Unit for emission estimate is Gg.
For the central region (including Henan, Hubei, and Hunan provinces), the main crops are winter wheat and summer corn, and the harvest seasons of these two crops are the end of May and the end of September (MOA, 2000), respectively. The peak emissions in the eastern region (including Shanghai, Jiangsu, Zhejiang, Anhui, and Jiangxi provinces) are mainly distributed from May to July, and May, June, and July are the harvest seasons of rapeseed, wheat, and rice in the eastern regions, respectively. The northern plains of China (including Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, and Shandong provinces) include the largest agricultural area in the country, accounting for 34 % of the rural population, 27 % of the farmland, and 35 % of the harvest crops (NBSC, 2013c). These regions differ from the eastern and central parts firstly in the usage of firewood, since there firewood is also used as heating energy and therefore the consumption of firewood in winter is greater than in summer. In addition, for in-field straw burning, northern winter wheat and corn are mainly harvested in June and October, respectively. April and May are the sowing seasons of spring rice and soya beans. The north-eastern region (including Liaoning, Jilin, and Heilongjiang provinces) shows high values in October, April, and November. The high value in April was a result of burning activity. The peak in October was mainly due to the harvesting of corn, and November is the harvest season for rice. In the north-western region (including Shaanxi, Gansu, Qinghai, Ningxia, and Xinjiang provinces), the peaks in March, April and October are mainly due to burning activities for the next corn sowing, wheat sowing, and corn harvesting seasons, respectively.
Furthermore, the daily PM
Total PM
The total NMVOC emission in this study was 3474 Gg. The alkenes are the
major contributor of biomass burning NMVOC emissions. The contribution of
alkenes to the total NMVOC emission was approximately 34 %, more than
that of alkane (28 %), aromatics (24 %), alkynes (13 %), and
others (1%). Among these species, ethylene, acetylene, propylene, and
1-butylene are the major species of alkenes and alkynes, with the total
contribution accounting for 40.1 %. Ethane,
Comparison of the emissions inventory derived by this study with the emissions estimated by previous studies.
The Monte Carlo method is used to analyse the uncertainty of this emission
inventory, as it has been used in uncertainty estimation for many inventory
studies (e.g. Streets et al., 2003; Zhao et al., 2011, 2012). Activity data
(Zheng et al., 2009) and EFs (Zhao et al., 2011) are assumed to be normal
distributions. The coefficients of variation (CV, the standard deviation
divided by the mean) of activity data and EFs were obtained from the literature. The CVs of activity data for firewood and straw burning were set as
20 % (Zhao et al., 2011; Ni et al., 2015). As the source of activity data
for livestock excrement is the same as that for crop straw burning (i.e.
government statistical data), the CV was also set as 20 %. MCD64A1-burned
data products have been shown to be reliable in large fires (Giglio et al.,
2013), and the CV of burned area of forest and grassland fires is from the
reported standard deviation (Giglio et al., 2010). The biomass fuel loadings
(Saatchi et al., 2011; Shi et al., 2015) and combustion factors (van der Werf
et al., 2010) of forest and grassland fires were within a CV of approximately
50 %. The CVs of the EFs for each pollutant for each biomass burning type
are shown in the Supplement (Sects. S8 and S9). The range of emissions was
calculated by averaging 20 000 Monte Carlo simulations with a 95 %
confidence interval. From the perspective of source, the uncertainty of
forest fires (ranging from
In this paper, the national biomass burning emission inventories published
after 2000 have been compared to those produced by our study (see Fig. 10). It
could be found that the relatively high difference (range from
In this study, a comprehensive biomass burning emission inventory with high
spatial and temporal resolution was developed for mainland China for 2012,
based on county-level activity data, satellite data, and updated
source-specific EFs. The emission inventory includes domestic and in-field
straw burning, firewood and livestock excrement burning, and burning by
forest and grassland fires. The total annual emissions of SO
Domestic straw burning, in-field straw burning, and firewood burning are the
major biomass burning sources, while the largest contributing source to
various pollutants is different. Domestic straw burning contributes most to
all of the pollutants considered, except for NO
EF and speciation of chemical species are the key parameters in emission
estimation. More localized EFs of different biomass fuel types within diverse
burning conditions and more detailed PM
The emission data are archived at Key Laboratory of Beijing on Regional Air Pollution Control and are available on request (y.zhou@bjut.edu.cn).
The authors declare that they have no conflict of interest.
The MODIS Thermal Anomalies/Fire products were provided by the Land Process
Distributed Active Archive Center (LPDAAC). The China Land Cover product and
the 1 km population distribution data set was provided by the National Science
& Technology Infrastructure of China, National Earth System Science Data Sharing Infrastructure (