4.3.4 Chemical Species Contributing to N Deposition
The contributions of different Nr species to total deposition estimated by recent
studies are summarized in Table 4.2. For all the national- and regional-scale simulations, NH x deposition accounts for 60–80% of total N deposition in China (Zheng
et al. 2014; Huang et al. 2015; Zhao et al. 2017a; Xu et al. 2018), reflecting the
intensity of agricultural activities in China. Figure 4.2 shows the spatial distribution
of percentage contributions of NH x deposition to annual total N deposition over
China using the GEOS-Chem model results from Zhao et al. (2017a). NH x deposition generally contributes more than NO y deposition except for some areas in
northwest China.
For components of total NH x deposition, GEOS-Chem model simulations for
China and the Yangtze River Basin estimated that more NH x comes via wet
deposition (65–70% of NH x deposition) (Zhao et al. 2017a, Xu et al. 2018).
CMAQ model simulations for Guangdong province showed a smaller contribution
from wet deposition (38% of total NH x deposition) (Huang et al. 2015). Because of a
higher dry deposition velocity for the soluble gaseous phase than the aerosol phase,
NH x is more likely deposited as gaseous NH 3 (70–90% of NH x dry deposition) in all
simulations (Table 4.2). Wet NO 3
À deposition contributes 40–65% of total NO y
deposition. Various oxidized Nr species are removed by dry deposition, but more
than 90% are deposited as HNO 3 , NO 2 and NO 3
À aerosol. Other species such as
isoprene nitrate, N 2 O 5 , PANs, alkyl nitrates and HONO make small but not negligible contributions to N deposition to China (Table 4.2).
Table 4.2 Atmospheric Nr species contributing to N deposition (Unit: Tg N year
À1
)
Deposition regions
and fluxes
China
a
China
b
Yangtze River
Basin
c
North China
Plain
d
Guangdong
e
NH x Total
10.2
5.4
21.9
36.2
18.3
Wet NH 4
+
6.6
15.5
7
Dry NH 3
2.6
4.5
10.7
Dry NH 4
+ aerosol
1.0
1.9
0.6
NO y Total
6.2
2.6
11
10.8
7.8
Wet NO 3
À
3.4
7.1
3.1
Dry HNO 3
1.7
2.2
2.7
Dry NO 2
0.3
0.47
0.55
Dry isoprene nitrates 0.13
0.19
Dry N 2 O 5
0.057
0.056
Dry PANs
3
0.058
0.11
Dry NO 3
À aerosol
0.5
0.88
1.3
Dry alkyl nitrates
0.009
0.036
Dry HONO
0.10
a GEOS-Chem model results from Zhao et al. (2017a) averaged over 2008–2012
b
CMAQ model results from Zheng et al. (2014) for the year 2010
c GEOS-Chem model results from Xu et al. (2018) for the year 2010
d
FRAME model results from Zhang et al. (2011) for the year 2008
e CMAQ model results from Huang et al. (2015) for the year 2006
4 Modelling Atmospheric Nitrogen Deposition in China
79
The contributions of different Nr species to total deposition estimated by recent
studies are summarized in Table 4.2. For all the national- and regional-scale simulations, NH x deposition accounts for 60–80% of total N deposition in China (Zheng
et al. 2014; Huang et al. 2015; Zhao et al. 2017a; Xu et al. 2018), reflecting the
intensity of agricultural activities in China. Figure 4.2 shows the spatial distribution
of percentage contributions of NH x deposition to annual total N deposition over
China using the GEOS-Chem model results from Zhao et al. (2017a). NH x deposition generally contributes more than NO y deposition except for some areas in
northwest China.
For components of total NH x deposition, GEOS-Chem model simulations for
China and the Yangtze River Basin estimated that more NH x comes via wet
deposition (65–70% of NH x deposition) (Zhao et al. 2017a, Xu et al. 2018).
CMAQ model simulations for Guangdong province showed a smaller contribution
from wet deposition (38% of total NH x deposition) (Huang et al. 2015). Because of a
higher dry deposition velocity for the soluble gaseous phase than the aerosol phase,
NH x is more likely deposited as gaseous NH 3 (70–90% of NH x dry deposition) in all
simulations (Table 4.2). Wet NO 3
À deposition contributes 40–65% of total NO y
deposition. Various oxidized Nr species are removed by dry deposition, but more
than 90% are deposited as HNO 3 , NO 2 and NO 3
À aerosol. Other species such as
isoprene nitrate, N 2 O 5 , PANs, alkyl nitrates and HONO make small but not negligible contributions to N deposition to China (Table 4.2).
Table 4.2 Atmospheric Nr species contributing to N deposition (Unit: Tg N year
À1
)
Deposition regions
and fluxes
China
a
China
b
Yangtze River
Basin
c
North China
Plain
d
Guangdong
e
NH x Total
10.2
5.4
21.9
36.2
18.3
Wet NH 4
+
6.6
15.5
7
Dry NH 3
2.6
4.5
10.7
Dry NH 4
+ aerosol
1.0
1.9
0.6
NO y Total
6.2
2.6
11
10.8
7.8
Wet NO 3
À
3.4
7.1
3.1
Dry HNO 3
1.7
2.2
2.7
Dry NO 2
0.3
0.47
0.55
Dry isoprene nitrates 0.13
0.19
Dry N 2 O 5
0.057
0.056
Dry PANs
3
0.058
0.11
Dry NO 3
À aerosol
0.5
0.88
1.3
Dry alkyl nitrates
0.009
0.036
Dry HONO
0.10
a GEOS-Chem model results from Zhao et al. (2017a) averaged over 2008–2012
b
CMAQ model results from Zheng et al. (2014) for the year 2010
c GEOS-Chem model results from Xu et al. (2018) for the year 2010
d
FRAME model results from Zhang et al. (2011) for the year 2008
e CMAQ model results from Huang et al. (2015) for the year 2006
4 Modelling Atmospheric Nitrogen Deposition in China
79