Last but not least, emissions estimates are uncertain due to incomplete knowledge
of underlying data (Zhao et al. 2011; Li et al. 2017b). In general, uncertainties of SO 2
and NO x are small because their emissions are dominated by large sources. Many of
the uncertainties in bottom-up emissions are also systematic and may have less
impact on emission trends (Lu et al. 2011), but noncompliance with regulations due
to lack of inspection will lead to differences between estimated and real-world
efficiencies of emission control facilities (e.g., Wang et al. 2015) and impact the
validity of estimated emission trends. Specifically, the effectiveness of the measures
targeting small and scattered emitting sources (e.g., phase out small, high-emitting
factories and eliminate small coal-fired industrial boilers) is difficult to validate,
which may lead to higher uncertainty ranges in emission estimates for the most
recent years.
2.4 Evolution of NH 3 Emissions
Over the past 30 years, China has undergone dramatic changes and significant
economic development, and NH 3 emissions have changed correspondingly (Kang
et al. 2016). Figure 2.5 illustrates the trends in total NH 3 emissions, which are
divided into fertilizer application, livestock waste, and other minor sources. Total
emissions increased from 5.9 to 11.1 Tg between 1980 and 1996 and then decreased
to 9.7 Tg in 2012. The most important contributor was livestock waste management,
accounting for approximately 50% of the total budget. Due to the extremely high
consumption and high volatility of ABC (ammonium bicarbonate) and urea, synthetic fertilizer application was responsible for 30–43% of the total emissions,
second only to livestock waste. However, in Europe and the United States, where
less-volatile synthetic fertilizers such as AN (ammonium nitrate) and AS (ammonium sulfate) are more popular (Bouwman and VanderHoek 1997), livestock waste
overwhelmingly dominates the NH 3 emissions inventory (Ferm 1998). These two
primary sources combined accounted for 80–90% of the total emissions budget, with
other minor sources accordingly accounting for 10–20%.
2.4.1 Emission Estimates
Livestock waste was the largest source of NH 3 emissions in China from 1980 to
2012, contributing approximately 50% of total emissions each year. As shown in
Fig. 2.6, emissions increased from 2.9 Tg in 1980 to 6.2 Tg in 2005, more than
doubling during this period, and then decreased to 5.0 Tg in 2012. We divided
livestock NH 3 emissions from 1980 to 2012 into four phases. In the first phase
(1980–1990), emissions steadily increased with a mean growth rate of approximately 3%. Free-range production contributed most of the emissions (the population
of free-range animals represented more than 90% of the major livestock animals
26
Q. Zhang et al.
of underlying data (Zhao et al. 2011; Li et al. 2017b). In general, uncertainties of SO 2
and NO x are small because their emissions are dominated by large sources. Many of
the uncertainties in bottom-up emissions are also systematic and may have less
impact on emission trends (Lu et al. 2011), but noncompliance with regulations due
to lack of inspection will lead to differences between estimated and real-world
efficiencies of emission control facilities (e.g., Wang et al. 2015) and impact the
validity of estimated emission trends. Specifically, the effectiveness of the measures
targeting small and scattered emitting sources (e.g., phase out small, high-emitting
factories and eliminate small coal-fired industrial boilers) is difficult to validate,
which may lead to higher uncertainty ranges in emission estimates for the most
recent years.
2.4 Evolution of NH 3 Emissions
Over the past 30 years, China has undergone dramatic changes and significant
economic development, and NH 3 emissions have changed correspondingly (Kang
et al. 2016). Figure 2.5 illustrates the trends in total NH 3 emissions, which are
divided into fertilizer application, livestock waste, and other minor sources. Total
emissions increased from 5.9 to 11.1 Tg between 1980 and 1996 and then decreased
to 9.7 Tg in 2012. The most important contributor was livestock waste management,
accounting for approximately 50% of the total budget. Due to the extremely high
consumption and high volatility of ABC (ammonium bicarbonate) and urea, synthetic fertilizer application was responsible for 30–43% of the total emissions,
second only to livestock waste. However, in Europe and the United States, where
less-volatile synthetic fertilizers such as AN (ammonium nitrate) and AS (ammonium sulfate) are more popular (Bouwman and VanderHoek 1997), livestock waste
overwhelmingly dominates the NH 3 emissions inventory (Ferm 1998). These two
primary sources combined accounted for 80–90% of the total emissions budget, with
other minor sources accordingly accounting for 10–20%.
2.4.1 Emission Estimates
Livestock waste was the largest source of NH 3 emissions in China from 1980 to
2012, contributing approximately 50% of total emissions each year. As shown in
Fig. 2.6, emissions increased from 2.9 Tg in 1980 to 6.2 Tg in 2005, more than
doubling during this period, and then decreased to 5.0 Tg in 2012. We divided
livestock NH 3 emissions from 1980 to 2012 into four phases. In the first phase
(1980–1990), emissions steadily increased with a mean growth rate of approximately 3%. Free-range production contributed most of the emissions (the population
of free-range animals represented more than 90% of the major livestock animals
26
Q. Zhang et al.