20% of the major livestock animals (EOCAIY 2006), because the Chinese government encouraged large-scale intensive methods for livestock production to gradually
replace traditional free-range systems (CAAA 2009). In 2012, the class-specific
proportions of intensively reared animals for beef cattle, pigs, and laying hens
significantly increased to approximately 30%, 40%, and 70%, respectively. This
change tends to reduce livestock emissions due to the lower NH 3 EFs of the intensive
system compared to the free-range (EEA 2013).
The interannual variation in fertilizer emissions reflects the changes in the
fertilizer consumption and farming practices in China. The key factor is the temporal
change in the contribution of urea and ABC over recent decades. During the 1980s,
ABC represented a substantial fraction of synthetic fertilizers used in China, and
because of its high volatility (Zhu et al. 1989), emissions from this kind of chemical
fertilizer dominated in this period. However, ABC was inefficient for crop production because of the low N content (17% N) and high N loss. In the mid-1990s, China
introduced the technology of urea production, which resulted in widespread application (Zhang et al. 2012b). Urea, characterized by high N concentration (46% N),
has gradually replaced ABC and become the dominant chemical fertilizer used in
cropland over the last 20 years. This transition accounted for the decline of NH 3
emissions from synthetic fertilizer in China because of the much lower NH 3 EFs for
urea than ABC.
2.4.3 Comparisons Among Bottom-Up Inventories
NH 3 emissions inventories of Kang et al. (2016) provide a detailed description of
interannual variation from 1980 to 2012 in China. A comparison between this study
and the Regional Emission Inventory in Asia (REAS) is presented in Fig. 2.9a. The
figures from REAS for 1980 to 2000 and 2000–2008 were derived from version 1.1
(Ohara et al. 2007) and 2.1 (Kurokawa et al. 2013), respectively. Note that the
interannual variability in the emissions in Kang et al. (2016) was generally consistent
with that in REAS before 1996. However, after that year the annual trend of
emissions in Kang et al. (2016) differed from those in REAS. In addition, the NH 3
emissions in REAS were generally higher than those in Kang et al. (2016). These
differences are likely attributable to differences in the estimations of synthetic
fertilizer emissions, discussed below.
In REAS, NH 3 emissions from animal manure applied as fertilizer were included
as a category of fertilizer emissions (Yan et al. 2003). NH 3 from the application of
animal waste onto croplands was 2.8 Tg in 2000 in REAS, accounting for approximately 60% of the total fertilizer emissions in that year. To render these two
inventories comparable, we excluded the application of animal waste from the
fertilizer emissions in REAS using the value for 2000. A comparison of the emissions from synthetic fertilizer application is presented in Fig. 2.9b. We found that the
REAS values were 20–50% higher than ours in 2000–2005, and this percentage rose
to 100% by 2008, which could be largely responsible for the differences of total
emissions between REAS and Kang et al. (2016) in the 2000s. It should be noted that
2 Anthropogenic Emissions of SO 2 , NO x , and NH 3 in China
31
replace traditional free-range systems (CAAA 2009). In 2012, the class-specific
proportions of intensively reared animals for beef cattle, pigs, and laying hens
significantly increased to approximately 30%, 40%, and 70%, respectively. This
change tends to reduce livestock emissions due to the lower NH 3 EFs of the intensive
system compared to the free-range (EEA 2013).
The interannual variation in fertilizer emissions reflects the changes in the
fertilizer consumption and farming practices in China. The key factor is the temporal
change in the contribution of urea and ABC over recent decades. During the 1980s,
ABC represented a substantial fraction of synthetic fertilizers used in China, and
because of its high volatility (Zhu et al. 1989), emissions from this kind of chemical
fertilizer dominated in this period. However, ABC was inefficient for crop production because of the low N content (17% N) and high N loss. In the mid-1990s, China
introduced the technology of urea production, which resulted in widespread application (Zhang et al. 2012b). Urea, characterized by high N concentration (46% N),
has gradually replaced ABC and become the dominant chemical fertilizer used in
cropland over the last 20 years. This transition accounted for the decline of NH 3
emissions from synthetic fertilizer in China because of the much lower NH 3 EFs for
urea than ABC.
2.4.3 Comparisons Among Bottom-Up Inventories
NH 3 emissions inventories of Kang et al. (2016) provide a detailed description of
interannual variation from 1980 to 2012 in China. A comparison between this study
and the Regional Emission Inventory in Asia (REAS) is presented in Fig. 2.9a. The
figures from REAS for 1980 to 2000 and 2000–2008 were derived from version 1.1
(Ohara et al. 2007) and 2.1 (Kurokawa et al. 2013), respectively. Note that the
interannual variability in the emissions in Kang et al. (2016) was generally consistent
with that in REAS before 1996. However, after that year the annual trend of
emissions in Kang et al. (2016) differed from those in REAS. In addition, the NH 3
emissions in REAS were generally higher than those in Kang et al. (2016). These
differences are likely attributable to differences in the estimations of synthetic
fertilizer emissions, discussed below.
In REAS, NH 3 emissions from animal manure applied as fertilizer were included
as a category of fertilizer emissions (Yan et al. 2003). NH 3 from the application of
animal waste onto croplands was 2.8 Tg in 2000 in REAS, accounting for approximately 60% of the total fertilizer emissions in that year. To render these two
inventories comparable, we excluded the application of animal waste from the
fertilizer emissions in REAS using the value for 2000. A comparison of the emissions from synthetic fertilizer application is presented in Fig. 2.9b. We found that the
REAS values were 20–50% higher than ours in 2000–2005, and this percentage rose
to 100% by 2008, which could be largely responsible for the differences of total
emissions between REAS and Kang et al. (2016) in the 2000s. It should be noted that
2 Anthropogenic Emissions of SO 2 , NO x , and NH 3 in China
31