4.1 Introduction
Rapid growth of anthropogenic activities such as agriculture and fossil fuel combustion has greatly increased global emissions of reactive nitrogen (Nr, such as NO x
and NH 3 ) to the atmosphere (Galloway et al. 2008). Anthropogenic Nr emissions
increased from 15 Tg N year
À1 in 1860 to more than 200 Tg N year
À1 in 2008
(Galloway and Cowling 2002; Canfield et al. 2010). Their removal through dry and
wet deposition, the ultimate fate of Nr in the atmosphere, is a critical component of
biogeochemical cycling (Gruber and Galloway 2008; Wang et al. 2013).
Wet deposition removes airborne pollutants by incorporating them into precipitation (rain, snow, hail, etc.) and dry deposition through turbulence or gravity. The
efficiency of wet deposition is mostly determined by the solubility of Nr species,
precipitation type (rain vs. snow) and precipitation intensity. The efficiency of dry
deposition depends on the solubility of Nr species at the surface and the physical,
chemical and biological activity of the surface (e.g. vegetation, water, etc.), as well
as the local meteorological conditions (e.g. atmospheric stability).
The lifetimes of Nr species generally vary from few hours (e.g. NH 3 and HNO 3 )
to several days (e.g. NO x and ammonium and nitrate aerosols) (Liang et al. 1998;
Zheng et al. 2002; Hertel et al. 2006). The short lifetimes and heterogeneous
distribution of their emissions make it difficult to fully represent their deposition
fluxes by the sparse surface measurement networks. In addition, current observations
in China only cover some Nr species, and there are few direct observations of dry
deposition. Numerical models, which calculate the deposition of each Nr species at
high spatial and temporal resolution, can help us better understand N deposition at
regional or national scales and develop control strategies for alleviating negative
effects of N deposition (Liu et al. 2011, 2017). This chapter provides an overview of
numerical approaches and a summary of recent modelling studies on atmospheric N
deposition in China.
4.2 Numerical Modelling Approaches for N Deposition
4.2.1 Wet Deposition Parameterization
Global and regional atmospheric chemistry models simulate the physical and chemical transformation of Nr species in the atmosphere. These models calculate deposition of chemical species through parameterization. Wet deposition
parameterization calculates in-cloud rainout and below-cloud washout considering
cloud microphysics, cloud-water phase chemical reactions and other processes.
Models generally distinguish between two types of precipitation: convective precipitation from convective updrafts and large-scale precipitation from frontal systems or
other meteorological processes (Jacob 1999).
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L. Zhang et al.
Rapid growth of anthropogenic activities such as agriculture and fossil fuel combustion has greatly increased global emissions of reactive nitrogen (Nr, such as NO x
and NH 3 ) to the atmosphere (Galloway et al. 2008). Anthropogenic Nr emissions
increased from 15 Tg N year
À1 in 1860 to more than 200 Tg N year
À1 in 2008
(Galloway and Cowling 2002; Canfield et al. 2010). Their removal through dry and
wet deposition, the ultimate fate of Nr in the atmosphere, is a critical component of
biogeochemical cycling (Gruber and Galloway 2008; Wang et al. 2013).
Wet deposition removes airborne pollutants by incorporating them into precipitation (rain, snow, hail, etc.) and dry deposition through turbulence or gravity. The
efficiency of wet deposition is mostly determined by the solubility of Nr species,
precipitation type (rain vs. snow) and precipitation intensity. The efficiency of dry
deposition depends on the solubility of Nr species at the surface and the physical,
chemical and biological activity of the surface (e.g. vegetation, water, etc.), as well
as the local meteorological conditions (e.g. atmospheric stability).
The lifetimes of Nr species generally vary from few hours (e.g. NH 3 and HNO 3 )
to several days (e.g. NO x and ammonium and nitrate aerosols) (Liang et al. 1998;
Zheng et al. 2002; Hertel et al. 2006). The short lifetimes and heterogeneous
distribution of their emissions make it difficult to fully represent their deposition
fluxes by the sparse surface measurement networks. In addition, current observations
in China only cover some Nr species, and there are few direct observations of dry
deposition. Numerical models, which calculate the deposition of each Nr species at
high spatial and temporal resolution, can help us better understand N deposition at
regional or national scales and develop control strategies for alleviating negative
effects of N deposition (Liu et al. 2011, 2017). This chapter provides an overview of
numerical approaches and a summary of recent modelling studies on atmospheric N
deposition in China.
4.2 Numerical Modelling Approaches for N Deposition
4.2.1 Wet Deposition Parameterization
Global and regional atmospheric chemistry models simulate the physical and chemical transformation of Nr species in the atmosphere. These models calculate deposition of chemical species through parameterization. Wet deposition
parameterization calculates in-cloud rainout and below-cloud washout considering
cloud microphysics, cloud-water phase chemical reactions and other processes.
Models generally distinguish between two types of precipitation: convective precipitation from convective updrafts and large-scale precipitation from frontal systems or
other meteorological processes (Jacob 1999).
68
L. Zhang et al.