6.1 Sector Descriptions and Overview
Soils and vegetation can be a source or sink for atmospheric ammonia (NH3) emissions due to nitrogen input rates, atmospheric conditions and biological processes. In other words, their flux is bidirectional. The direction and magnitude of the exchange depend on the concentration gradient between the canopy and the atmosphere. Natural vegetation and soils will emit NH3 as a result of biogenic processes. Vegetation and soil associated with agricultural croplands will receive a higher input of nitrogen than non-agricultural lands during periods of fertilizer application (which refers to any nitrogen-based compound, or mixture containing such a compound, that is applied to land to improve plant fitness) and can emit NH3 similarly.
The SCCs that compose this sector in the 2023 NEI are provided in Table 6.1. EPA-estimated emissions of these SCCs are discussed further below.
| SCC | SCC Level 2 | SCC Level 3 | SCC Level 4 |
|---|---|---|---|
| 2801700100 | Agriculture Production - Crops | Fertilizer Application | Total: Anthropogenic |
| 2803001000 | Non-Agriculture | Biological Activity | Total: Biogenic |