2.1 Introduction
Understanding emissions in China is essential for studies of atmospheric chemistry
and climate. Specifically, SO 2 , NO x , and NH 3 from anthropogenic sources cause
severe air pollution and lead to adverse impacts on human health and ecosystems
over China. Anthropogenic emissions of sulfur dioxide (SO 2 ) have resulted in
greatly increased sulfur deposition and atmospheric sulfate loadings near industrialized areas (Smith et al. 2011). Sulfuric acid deposition can be detrimental to
ecosystems, harming aquatic animals and plants and damaging a wide range of
terrestrial plant life. SO 2 can be adsorbed onto the surface of mineral dust as
adsorbed sulfite that is oxidized to form sulfate, which turn out the major source
for the growth of fine particles, and subsequently lead to visibility impairment, acid
rain, and haze formation (Kulmala 2003; Yan and Wu 2017). Meanwhile, sulfate
aerosols also come from (1) gas-phase SO 2 oxidation by hydroxyl radical and
(2) in-cloud oxidation of dissolved SO 2 (e.g., Shen et al. 2012). Sulfate aerosols
formed from sulfur dioxide also have a significant effect on global and regional
climate. Sulfate aerosols reflect sunlight into space and also act as cloud condensation nuclei (CCN); increased numbers of CCN tend to make clouds more reflective
and change their lifetimes, causing a net cooling. The radiative forcing change
wrought by sulfate aerosols may be second only to that caused by carbon dioxide,
albeit in the opposite direction (Forster et al. 2007). Sulfur is ubiquitous in the
biosphere and often occurs in relatively high concentrations in fossil fuels, with coal
and crude oil deposits commonly containing 1–2% sulfur by weight. The combustion of coal and oil fuel accounts for more than 75% of global SO 2 emissions
(Klimont et al. 2013), a figure found to be similar when focusing on the Chinese
domain (Smith et al. 2001, 2011). Anthropogenic SO 2 emissions in China have
accounted for over 30% of global emissions since 2010 (Hoesly et al. 2018). Lu et al.
(2011) showed that SO 2 emissions over China, calculated from all major anthropogenic sources as well as scheduled biomass burning events by the agricultural sector
in order to clear vegetation and rejuvenate croplands, increased from $24 Tg in 1996
to $31 Tg in 2010, including fluctuations due to the onset of environmental
protection measures as well as the international economic crisis.
Nitrogen oxides (NO x ), including nitrogen dioxide (NO 2 ) and nitric oxide (NO),
are atmospheric trace gases with a short lifetime, and they actively participate in the
formation of tropospheric ozone and secondary aerosols and thus harm human health
(Seinfeld and Pandis 2006). Increasing nitrate/sulfate ratios in precipitation have
been observed in monitored cities in China, attributable to increasing NO x emissions
(Zhao et al. 2009). In addition, NO x may lead to climate forcing effects via ozone
formation or via secondary aerosols (Solomon et al. 2007). China is the largest NO x
emitter and thought to contribute 24% of global NO x emissions (Hoesly et al. 2018).
Power plants and vehicles are two of the largest sources of NO x emissions in China,
contributing 28.4% and 25.4% of the total anthropogenic emissions in 2010, respectively, according to the study of Zhao et al. (2013a). As a consequence of its rapidly
14
Q. Zhang et al.
Understanding emissions in China is essential for studies of atmospheric chemistry
and climate. Specifically, SO 2 , NO x , and NH 3 from anthropogenic sources cause
severe air pollution and lead to adverse impacts on human health and ecosystems
over China. Anthropogenic emissions of sulfur dioxide (SO 2 ) have resulted in
greatly increased sulfur deposition and atmospheric sulfate loadings near industrialized areas (Smith et al. 2011). Sulfuric acid deposition can be detrimental to
ecosystems, harming aquatic animals and plants and damaging a wide range of
terrestrial plant life. SO 2 can be adsorbed onto the surface of mineral dust as
adsorbed sulfite that is oxidized to form sulfate, which turn out the major source
for the growth of fine particles, and subsequently lead to visibility impairment, acid
rain, and haze formation (Kulmala 2003; Yan and Wu 2017). Meanwhile, sulfate
aerosols also come from (1) gas-phase SO 2 oxidation by hydroxyl radical and
(2) in-cloud oxidation of dissolved SO 2 (e.g., Shen et al. 2012). Sulfate aerosols
formed from sulfur dioxide also have a significant effect on global and regional
climate. Sulfate aerosols reflect sunlight into space and also act as cloud condensation nuclei (CCN); increased numbers of CCN tend to make clouds more reflective
and change their lifetimes, causing a net cooling. The radiative forcing change
wrought by sulfate aerosols may be second only to that caused by carbon dioxide,
albeit in the opposite direction (Forster et al. 2007). Sulfur is ubiquitous in the
biosphere and often occurs in relatively high concentrations in fossil fuels, with coal
and crude oil deposits commonly containing 1–2% sulfur by weight. The combustion of coal and oil fuel accounts for more than 75% of global SO 2 emissions
(Klimont et al. 2013), a figure found to be similar when focusing on the Chinese
domain (Smith et al. 2001, 2011). Anthropogenic SO 2 emissions in China have
accounted for over 30% of global emissions since 2010 (Hoesly et al. 2018). Lu et al.
(2011) showed that SO 2 emissions over China, calculated from all major anthropogenic sources as well as scheduled biomass burning events by the agricultural sector
in order to clear vegetation and rejuvenate croplands, increased from $24 Tg in 1996
to $31 Tg in 2010, including fluctuations due to the onset of environmental
protection measures as well as the international economic crisis.
Nitrogen oxides (NO x ), including nitrogen dioxide (NO 2 ) and nitric oxide (NO),
are atmospheric trace gases with a short lifetime, and they actively participate in the
formation of tropospheric ozone and secondary aerosols and thus harm human health
(Seinfeld and Pandis 2006). Increasing nitrate/sulfate ratios in precipitation have
been observed in monitored cities in China, attributable to increasing NO x emissions
(Zhao et al. 2009). In addition, NO x may lead to climate forcing effects via ozone
formation or via secondary aerosols (Solomon et al. 2007). China is the largest NO x
emitter and thought to contribute 24% of global NO x emissions (Hoesly et al. 2018).
Power plants and vehicles are two of the largest sources of NO x emissions in China,
contributing 28.4% and 25.4% of the total anthropogenic emissions in 2010, respectively, according to the study of Zhao et al. (2013a). As a consequence of its rapidly
14
Q. Zhang et al.