lead, in those regions, to a larger build-up of NH 3 and hence larger observed columns
and a larger qualitative discrepancy with the emission inventory.
Within our studied period, NO x emissions have also increased significantly,
mainly from industrial and energy sources (~90%), residential combustion, and
transport use which account for 11%. The highest share of industry combustion to
total NO x emissions is observed in the well-developed Eastern China, where the
highest NO x emission density in China is also found (Fig. 5.5d, e), which is
significantly correlated to socioeconomic factors (per capita GDP, urbanization,
and population density). However, NO x emissions decrease by 10–26% in major
cities (e.g. Beijing, Guangzhou, Shenzhen) from 2005 to 2012; later, Tianjin, Hebei,
Henan, Shandong, and Hubei Province also have lower NO x emission since 2010,
coinciding with the enforcement of Chinese twelfth “Five-Year Plan”, which specified for the first time a national commitment to reduce NO x emissions (Foy et al.
2016; Xue et al. 2013).
N 2 O is largely biogenic and derived mainly from agricultural sector (~50%),
followed by forest and surface water, with these together accounting for 93% of all
N 2 O emission in China. Thus, the regions with higher N 2 O emissions are mainly
located in agriculture-dominated regions, such as the North China Plain, Lianghu
Plain (in Hubei and Hunan provinces), Yangtze River Delta, and Pearl River Delta
(Fig. 5.5e). It is because good climatic and soil conditions (high temperature and
humidity) are necessary for the biological activity of microorganisms
(e.g. nitrification and denitrification) in the soil to emit N 2 O (Kulkarni et al.
2008). Meanwhile, human activities increase the Nr inputs that can also enhance
the activities of microorganisms (Chen et al. 2008; Lu et al. 2006). For
non-biogenic sources of N 2 O emission, great spatial variation occurred across
China with higher values in relatively developed areas, such as 54% in Shanghai,
because the non-biogenic sources of N 2 O mainly are fossil fuel combustion and
industrial processes; in the contrary, for less developed regions like Tibet, this value
is only 3%.
As for two main N loss ways, surface N runoff occurred mainly in South China
where high rainfall and high N surpluses co-occur (Fig. 5.5f, g); North China was the
main hotspot of N leaching to groundwater because the rainfall is concentrated in
summer and flood irrigation is practised in the region.
5.4.3 Comparisons with Earlier Atmospheric N Budgets of
China
To our knowledge, the current N budget is the first one to combine all subsystems
together to establish a well-rounded and comprehensive inventory which describe Nr
cascading among subsystems within China in details. Earlier studies differed in
scope, scale, and methods (Cui et al. 2013; Gu et al. 2013; Hou et al. 2013; Ma et al.
2013; Ti et al. 2012), with some focused primarily on agricultural systems.
5 Reactive Nitrogen Budgets in China
101
and a larger qualitative discrepancy with the emission inventory.
Within our studied period, NO x emissions have also increased significantly,
mainly from industrial and energy sources (~90%), residential combustion, and
transport use which account for 11%. The highest share of industry combustion to
total NO x emissions is observed in the well-developed Eastern China, where the
highest NO x emission density in China is also found (Fig. 5.5d, e), which is
significantly correlated to socioeconomic factors (per capita GDP, urbanization,
and population density). However, NO x emissions decrease by 10–26% in major
cities (e.g. Beijing, Guangzhou, Shenzhen) from 2005 to 2012; later, Tianjin, Hebei,
Henan, Shandong, and Hubei Province also have lower NO x emission since 2010,
coinciding with the enforcement of Chinese twelfth “Five-Year Plan”, which specified for the first time a national commitment to reduce NO x emissions (Foy et al.
2016; Xue et al. 2013).
N 2 O is largely biogenic and derived mainly from agricultural sector (~50%),
followed by forest and surface water, with these together accounting for 93% of all
N 2 O emission in China. Thus, the regions with higher N 2 O emissions are mainly
located in agriculture-dominated regions, such as the North China Plain, Lianghu
Plain (in Hubei and Hunan provinces), Yangtze River Delta, and Pearl River Delta
(Fig. 5.5e). It is because good climatic and soil conditions (high temperature and
humidity) are necessary for the biological activity of microorganisms
(e.g. nitrification and denitrification) in the soil to emit N 2 O (Kulkarni et al.
2008). Meanwhile, human activities increase the Nr inputs that can also enhance
the activities of microorganisms (Chen et al. 2008; Lu et al. 2006). For
non-biogenic sources of N 2 O emission, great spatial variation occurred across
China with higher values in relatively developed areas, such as 54% in Shanghai,
because the non-biogenic sources of N 2 O mainly are fossil fuel combustion and
industrial processes; in the contrary, for less developed regions like Tibet, this value
is only 3%.
As for two main N loss ways, surface N runoff occurred mainly in South China
where high rainfall and high N surpluses co-occur (Fig. 5.5f, g); North China was the
main hotspot of N leaching to groundwater because the rainfall is concentrated in
summer and flood irrigation is practised in the region.
5.4.3 Comparisons with Earlier Atmospheric N Budgets of
China
To our knowledge, the current N budget is the first one to combine all subsystems
together to establish a well-rounded and comprehensive inventory which describe Nr
cascading among subsystems within China in details. Earlier studies differed in
scope, scale, and methods (Cui et al. 2013; Gu et al. 2013; Hou et al. 2013; Ma et al.
2013; Ti et al. 2012), with some focused primarily on agricultural systems.
5 Reactive Nitrogen Budgets in China
101