The Chinese government set a goal of a 10% decrease in SO 2 emissions in the
11th 5-year plan (11th FYP, 2006–2010), and then efforts have been made to reduce
NO x emissions during the 12th FYP (2011–2015). Compared to the 2010 level, SO 2
and NO x emissions in the year 2015 are expected to decline by 8% and 10%,
respectively. It is the first time that China has taken steps to control NO x emissions.
Wang et al. (2013) evaluated the influence of changes in SO 2 and NO x emissions
from 2006 to 2015 on SNA concentrations over China. According to their calculations, SO 2 and NO x emissions in 2015 were 16.45% lower and 16.63% higher than
those in 2006. They used the GEOS-Chem chemical transport model, using the
standard scenario and the intex-B emission inventory for 2006, and the meteorology
field was for the year 2017. In the sensitivity test, SO 2 and NO x emissions were
replaced by 2015 emissions, with other emissions (including NH 3 ) and meteorology
remaining unchanged. The result showed that the decrease in SO 4
2À concentration
(10% to 19%) was almost equal to the reduction in SO 2 emissions (16.45%).
Interestingly, the NO 3
À concentration increased from 17% to 30%, which was
much higher than the increase in NO x emissions (16.6%). This is because the NH 3
emissions remained stable from 2006 to 2015 in their simulation, and the decrease in
the SO 4
2À concentration released excessive NH 3 to form NH 4 NO 3 . This possibility
was further supported by two recent studies (Lachatre et al. 2018; Liu et al. 2018a).
Zhao et al. (2013) also evaluated the impacts of controlling NO x emissions on
PM 2.5 concentrations at regional and national scales. Their results showed that under
the planned NO x control measures according to the 12th FYP, NO x emissions in
2015 would be 12.2% lower than in 2010, and under the accelerated NO x control
measures, NO x emissions would be 23.9% lower in 2015 than 2010. However, under
the two circumstances, the reduction in the PM 2.5 concentration was very small (less
than 5%) over the majority of East China, and there was even an increase in NO 3
À
concentrations over the North China Plain and the Yangtze River Delta during the
winter season. The increased NO 3
À concentration was due to the NH 3 -rich environment for inorganic aerosol chemistry and the NMVOC-sensitive photochemical
regime.
The Action Plan that was set in 2013 called for stricter emission control strategies.
Cai et al. (2017) estimated PM 2.5 and its precursors’ emissions in 2017 from the JingJin-Ji region (NO x emissions decreased by 31%, and NH 3 emissions increased by
10%) and assessed the PM 2.5 concentration change from 2012 to 2017. They found
that the PM 2.5 concentration over the Jing-Jin-Ji region in 2017 was 28.3% lower
than the 2012 level because of emission reductions. Regarding SNA aerosols, the
SO 4
2À concentration decreased because the SO 2 emissions decreased, the NH 4
+
concentration decreased by 14.5% despite the 10% increase in NH 3 emissions, and
the NO 3
À concentration varied little from 2012 to 2017. The decrease in the NH 4
+
concentration was mainly due to the decrease in SO 4
2À . The NO 3
À concentration
decreased in July because of emission reductions, but it increased significantly in
January despite the >27% decrease in NO x emissions due to the NH 3 -rich environment. Cai et al. (2017) recommended the synergistic emissions control of SO 2 , NO x ,
and NH 3 during NH 3 -rich seasons.
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Y. Pan et al.
11th 5-year plan (11th FYP, 2006–2010), and then efforts have been made to reduce
NO x emissions during the 12th FYP (2011–2015). Compared to the 2010 level, SO 2
and NO x emissions in the year 2015 are expected to decline by 8% and 10%,
respectively. It is the first time that China has taken steps to control NO x emissions.
Wang et al. (2013) evaluated the influence of changes in SO 2 and NO x emissions
from 2006 to 2015 on SNA concentrations over China. According to their calculations, SO 2 and NO x emissions in 2015 were 16.45% lower and 16.63% higher than
those in 2006. They used the GEOS-Chem chemical transport model, using the
standard scenario and the intex-B emission inventory for 2006, and the meteorology
field was for the year 2017. In the sensitivity test, SO 2 and NO x emissions were
replaced by 2015 emissions, with other emissions (including NH 3 ) and meteorology
remaining unchanged. The result showed that the decrease in SO 4
2À concentration
(10% to 19%) was almost equal to the reduction in SO 2 emissions (16.45%).
Interestingly, the NO 3
À concentration increased from 17% to 30%, which was
much higher than the increase in NO x emissions (16.6%). This is because the NH 3
emissions remained stable from 2006 to 2015 in their simulation, and the decrease in
the SO 4
2À concentration released excessive NH 3 to form NH 4 NO 3 . This possibility
was further supported by two recent studies (Lachatre et al. 2018; Liu et al. 2018a).
Zhao et al. (2013) also evaluated the impacts of controlling NO x emissions on
PM 2.5 concentrations at regional and national scales. Their results showed that under
the planned NO x control measures according to the 12th FYP, NO x emissions in
2015 would be 12.2% lower than in 2010, and under the accelerated NO x control
measures, NO x emissions would be 23.9% lower in 2015 than 2010. However, under
the two circumstances, the reduction in the PM 2.5 concentration was very small (less
than 5%) over the majority of East China, and there was even an increase in NO 3
À
concentrations over the North China Plain and the Yangtze River Delta during the
winter season. The increased NO 3
À concentration was due to the NH 3 -rich environment for inorganic aerosol chemistry and the NMVOC-sensitive photochemical
regime.
The Action Plan that was set in 2013 called for stricter emission control strategies.
Cai et al. (2017) estimated PM 2.5 and its precursors’ emissions in 2017 from the JingJin-Ji region (NO x emissions decreased by 31%, and NH 3 emissions increased by
10%) and assessed the PM 2.5 concentration change from 2012 to 2017. They found
that the PM 2.5 concentration over the Jing-Jin-Ji region in 2017 was 28.3% lower
than the 2012 level because of emission reductions. Regarding SNA aerosols, the
SO 4
2À concentration decreased because the SO 2 emissions decreased, the NH 4
+
concentration decreased by 14.5% despite the 10% increase in NH 3 emissions, and
the NO 3
À concentration varied little from 2012 to 2017. The decrease in the NH 4
+
concentration was mainly due to the decrease in SO 4
2À . The NO 3
À concentration
decreased in July because of emission reductions, but it increased significantly in
January despite the >27% decrease in NO x emissions due to the NH 3 -rich environment. Cai et al. (2017) recommended the synergistic emissions control of SO 2 , NO x ,
and NH 3 during NH 3 -rich seasons.
126
Y. Pan et al.