Process-based NH3 Model
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Project Overview
Ammonia is an important atmospheric pollutant that combines with sulfuric acid and nitric acid to form aerosol sulfates and nitrate, respectively. These aerosol species are major components of fine particulate matter (PM) and contribute significantly to visibility impairment. In the United States, an estimated 55% of total ammonia emissions come from livestock and 24% from fertilizer use. Estimates of ammonia emissions factors are both highly variable and uncertain. Emissions factors vary depending on meteorological conditions and seasonal and regional differences in farming practices. Previous ammonia emissions inventories have not adequately characterized seasonal and geographical variations in emissions factors. For example, the ammonia emissions inventories generated by Pinder et al. (2003) calculated annual emissions inventories using seasonal average temperatures. However, recent chemical transport modeling suggests that daily and hourly variability in ammonia emissions is required to model accurately the formation of ammonium nitrate and ammonium sulfates.
Because of difference among animals and farming practices it is necessary to develop animal specific models for the major livestock categories including: dairy cows, beef cattle, hogs, chickens, and turkeys. The model considers each of the processes occurring on a typical livestock farm, and calculates the resulting ammonia emissions from each. By tracking the amount of manure through each stage at the farm and using mass conservation, the total ammonia emissions for each process and for the farm as a whole is estimated. The main processes treated in the model include the nitrogen excretion from the animals, animal housing, feedlot operation, manure storage and land application of manure.
The process-based ammonia emissions model developed for this study was described in detail in three separate project documents including the Science document (Zhang, et al., 2004); the Design Document (Wang, et al., 2005); and the Data Document for the Farm Emissions Model (Wang, et al., 2005).
In addition to the three reports, a final report provides a capsule summary of the governing equations, data requirements, and some preliminary results from the model. Much of the contents in the final report are from the two technical papers presented at the 14th International Emission Inventory Conference. Las Vegas, NV. (Zhang, et al., 2005; Mansell, et al., 2005). Chapter two of this report briefly describes the original technical approach proposed. Chapter three describes the revised technical approach in the development of the process-based ammonia model. Chapter four outlines the key governing equations in the Farm Emissions Model (FEM). Data requirements in the model are discussed in Chapter 5. Preliminary model results are described in Chapter 6. Chapter 7 describes additional data available for further evaluation. Chapter 8 outlines work that should be performed in the future.