Due to the bidirectional exchange of NH 3 between the atmosphere and surfaces,
the dry deposition of NH 3 is calculated using bidirectional NH 3 exchange models
(Nemitz et al. 2001; Pleim et al. 2013; Shen et al. 2016), where the total NH 3 flux (F t )
is calculated as the sum of bidirectional exchange with leaf stomata (F s ), deposition
to leaf cuticle (F w ) and bidirectional exchange with ground (F g ). The canopy flux
(F f ) was further calculated as the sum of F s and F w since they occur in parallel in the
canopy layer. The equations below show the definition and relation of each flux:
F t ¼ F s þ F w þ F g
ð3:10Þ
F f ¼ F s þ F w
ð3:11Þ
F t ¼
χ a À χ Z 0
ð Þ
R a
ð3:12Þ
F f ¼
χ Z 0
ð Þ À χ c
R b
ð3:13Þ
F s ¼
χ c À χ s
R s
ð3:14Þ
F w ¼
χ c
R w
ð3:15Þ
F g ¼
χ z 0
ð Þ À χ g
R g
ð3:16Þ
where χ a is NH 3 concentration measured at a height over the canopy; χ(z 0 ) NH 3
concentration at height of d + z 0 ; χ c , χ s and χ g canopy, stomatal and ground NH 3
compensation points, respectively; and R a , R b , R s , and R g aerodynamic, quasilaminar boundary layer, stomatal and cuticular, and ground resistances, respectively.
Based on Equations (3.10), (3.12), (3.13) and (3.16), χ(z 0 ) can be calculated using
the following equation:
χ z 0
ð Þ ¼
χ a  R a
À1
þ χ g  R g
À1
þ χ c  R b
À1
R a
À1
þ R g
À1
þ R b
À1
ð3:17Þ
46
X. Liu et al.
the dry deposition of NH 3 is calculated using bidirectional NH 3 exchange models
(Nemitz et al. 2001; Pleim et al. 2013; Shen et al. 2016), where the total NH 3 flux (F t )
is calculated as the sum of bidirectional exchange with leaf stomata (F s ), deposition
to leaf cuticle (F w ) and bidirectional exchange with ground (F g ). The canopy flux
(F f ) was further calculated as the sum of F s and F w since they occur in parallel in the
canopy layer. The equations below show the definition and relation of each flux:
F t ¼ F s þ F w þ F g
ð3:10Þ
F f ¼ F s þ F w
ð3:11Þ
F t ¼
χ a À χ Z 0
ð Þ
R a
ð3:12Þ
F f ¼
χ Z 0
ð Þ À χ c
R b
ð3:13Þ
F s ¼
χ c À χ s
R s
ð3:14Þ
F w ¼
χ c
R w
ð3:15Þ
F g ¼
χ z 0
ð Þ À χ g
R g
ð3:16Þ
where χ a is NH 3 concentration measured at a height over the canopy; χ(z 0 ) NH 3
concentration at height of d + z 0 ; χ c , χ s and χ g canopy, stomatal and ground NH 3
compensation points, respectively; and R a , R b , R s , and R g aerodynamic, quasilaminar boundary layer, stomatal and cuticular, and ground resistances, respectively.
Based on Equations (3.10), (3.12), (3.13) and (3.16), χ(z 0 ) can be calculated using
the following equation:
χ z 0
ð Þ ¼
χ a  R a
À1
þ χ g  R g
À1
þ χ c  R b
À1
R a
À1
þ R g
À1
þ R b
À1
ð3:17Þ
46
X. Liu et al.