## 2.22.3. Atmospheric Nitrogen Deposition[¶](#atmospheric-nitrogen-deposition "Permalink to this headline")
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CLM uses a single variable to represent the total deposition of mineral nitrogen onto the land surface, combining wet and dry deposition of NOy and NHx as a single flux (\\({NF}\_{ndep\\\_sminn}\\), gN m\-2 s\-1). This flux is intended to represent total reactive nitrogen deposited to the land surface which originates from the following natural and anthropogenic sources (Galloway et al. 2004): formation of NOx during lightning, NO\\({}\_{x }\\)and NH3 emission from wildfire, NOx emission from natural soils, NH3 emission from natural soils, vegetation, and wild animals, NOx and NH3 emission during fossil fuel combustion (both thermal and fuel NOx production), NOx and NH3 emission from other industrial processes, NOx and NH3 emission from fire associated with deforestation, NOx and NH3 emission from agricultural burning, NOx emission from agricultural soils, NH3 emission from agricultural crops, NH3 emission from agricultural animal waste, and NH3 emission from human waste and waste water. The deposition flux is provided as a spatially and (potentially) temporally varying dataset (see section [2.2.3.1](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Ecosystem/CLM50_Tech_Note_Ecosystem.html#atmospheric-coupling) for a description of the default input dataset).

The nitrogen deposition flux is assumed to enter the NH4+ pool, and is vertically distributed throughout the soil profile. Although N deposition inputs include both oxidized and reduced forms, CLM5 only reads in total N deposition. This approach is held over from CLM4.0, which only represented a single mineral nitrogen pool, however, real pathways for wet and dry nitrogen deposition can be more complex than currently represented in the CLM5.0, including release from melting snowpack and direct foliar uptake of deposited NOy ([Tye et al. 2005](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#tyeetal2005); [Vallano and Sparks, 2007](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#vallanosparks2007)).

In offline (uncoupled) CLM5.0 simulations monthly estimates of N deposition are provided, as opposed to decadal files supplied with previous versions of the model. In coupled simulations, N depositions fluxes are passed to the land model at the frequency of the time step (every half hour) through the coupler.

