4.3.5 Future Projection of N Deposition in China
There are only a few recent modelling studies projecting N deposition in China using
coupled climate-chemistry models and projected emission scenarios. For example,
the IPCC Representative Concentration Pathways (RCPs) define four different
scenarios (RCP2.6, RCP4.5, RCP6, RCP8.5) based on the radiative forcing value
in 2100. A pioneering global modelling investigation by Galloway et al. (2004)
projected the largest increases of N deposition in East Asia in the future. Large areas
of East Asia would receive more than 50 kg N ha
À1 year
À1 based on the IPCC92a
emission scenario. A more recent study using the multi-model mean results from the
Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
concluded that, under the IPCC RCP2.6 and RCP8.5 scenarios, N deposition in
East Asia would increase by 27% and 39% in the 2030s, respectively (Lamarque
et al. 2013). The CMAQ model simulation for China by Zhao et al. (2009)
implemented a projection of Nr emissions in 2020, based on the existing emission
control strategies, and found that the percentage of terrestrial areas in China with N
deposition exceeding the eutrophication critical load would increase from 12.1% in
2005 to 16.1% in 2020.
4.4 Conclusion and Outlook
This chapter has reviewed model parameterizations of deposition processes (wet and
dry deposition) and their recent applications to estimating N deposition to China.
Wet deposition in numerical models includes scavenging via both convective
updrafts and large-scale precipitation. Dry deposition is generally calculated as the
product of number density and dry deposition velocity, and most models parameterize dry deposition velocity based on the resistance-in-series model, which considers land surface properties and local meteorological conditions. More recent
developments of dry deposition parameterization consider detailed canopy structure
and co-deposition processes.
Recent model simulations have estimated that annual total N deposition fluxes to
China range from 7.9 Tg N year
À1 (Zheng et al. 2014) to 20.1 Tg N year
À1 (Lu and
Tian 2014) in the 2000s, with high deposition rates of more than 70 kg N ha
À1
year
À1 in Guangdong province (Huang et al. 2015) and the North China Plain
(Zhang et al. 2011). NH x deposition accounts for 60–80% of the total N deposition.
Annual wet and dry deposition fluxes to China are comparable, but some differences
exist in different model simulations. Because of the complexity of deposition
mechanisms, the uncertainty of input parameters and differences in the physicochemical properties of Nr components, there are still considerable uncertainties in
the numerical modelling of atmospheric N deposition.
Ammonia emissions from agricultural activities are the largest source of N
deposition in China. However, large uncertainties exist in current estimates of
Chinese ammonia emissions. Zhang et al. (2018) found that estimates of total
80
L. Zhang et al.
There are only a few recent modelling studies projecting N deposition in China using
coupled climate-chemistry models and projected emission scenarios. For example,
the IPCC Representative Concentration Pathways (RCPs) define four different
scenarios (RCP2.6, RCP4.5, RCP6, RCP8.5) based on the radiative forcing value
in 2100. A pioneering global modelling investigation by Galloway et al. (2004)
projected the largest increases of N deposition in East Asia in the future. Large areas
of East Asia would receive more than 50 kg N ha
À1 year
À1 based on the IPCC92a
emission scenario. A more recent study using the multi-model mean results from the
Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
concluded that, under the IPCC RCP2.6 and RCP8.5 scenarios, N deposition in
East Asia would increase by 27% and 39% in the 2030s, respectively (Lamarque
et al. 2013). The CMAQ model simulation for China by Zhao et al. (2009)
implemented a projection of Nr emissions in 2020, based on the existing emission
control strategies, and found that the percentage of terrestrial areas in China with N
deposition exceeding the eutrophication critical load would increase from 12.1% in
2005 to 16.1% in 2020.
4.4 Conclusion and Outlook
This chapter has reviewed model parameterizations of deposition processes (wet and
dry deposition) and their recent applications to estimating N deposition to China.
Wet deposition in numerical models includes scavenging via both convective
updrafts and large-scale precipitation. Dry deposition is generally calculated as the
product of number density and dry deposition velocity, and most models parameterize dry deposition velocity based on the resistance-in-series model, which considers land surface properties and local meteorological conditions. More recent
developments of dry deposition parameterization consider detailed canopy structure
and co-deposition processes.
Recent model simulations have estimated that annual total N deposition fluxes to
China range from 7.9 Tg N year
À1 (Zheng et al. 2014) to 20.1 Tg N year
À1 (Lu and
Tian 2014) in the 2000s, with high deposition rates of more than 70 kg N ha
À1
year
À1 in Guangdong province (Huang et al. 2015) and the North China Plain
(Zhang et al. 2011). NH x deposition accounts for 60–80% of the total N deposition.
Annual wet and dry deposition fluxes to China are comparable, but some differences
exist in different model simulations. Because of the complexity of deposition
mechanisms, the uncertainty of input parameters and differences in the physicochemical properties of Nr components, there are still considerable uncertainties in
the numerical modelling of atmospheric N deposition.
Ammonia emissions from agricultural activities are the largest source of N
deposition in China. However, large uncertainties exist in current estimates of
Chinese ammonia emissions. Zhang et al. (2018) found that estimates of total
80
L. Zhang et al.