This document discusses using an inverse modeling technique called FIDES to estimate ammonia (NH3) emissions from time-averaged concentration measurements. FIDES uses average concentration data, wind characteristics, and site layout to calculate source strengths that could have resulted in the observed concentrations. The technique was applied to data from cattle pens in Colorado. The model estimated average emissions of 4.7 g/m^2 per day and 41 g per head per day, with 53% of fed nitrogen emitted as NH3. Emissions decreased in the winter months as volatilization from surfaces reduced.

1. Inverse Modeling of NH3 Emissions
Using
Time-Averaged Concentrations
Kira Shonkwiler
Department of Atmospheric Science, Colorado State University

2. Inverse Modeling
 What if… wind
 You can’t directly Cattle Pens
North
measure emissions?
West Base
 The instruments are too
expensive? 700 m South
 You only know N
concentration?
 Know average concentration, wind
characteristics, and site layout…
 Can estimate how much was emitted for that location to report
that concentration!

3. FIDES
 Flux Interpretation by Dispersion Exchange
over Short-range (FIDES)
 Inverse model (inputs: u* and L)
 Solves the advection-dispersion equation
 Uses concentration ( ) from a location (x, z) to estimate
source strength of a different location (xs, zs)
 Cbgd is the constant background concentration
 S is the source strength
 D is a dispersion function
Loubet et al., 2001; 2010

4. FIDES
 Applied successfully in Europe
(Loubet et al., 2001; 2009; 2010)
 NH3 concentrations measured with high-speed
instrumentation
 Expensive
 Work at CSU is first attempt at modeling NH3
emissions from time-averaged data (i.e., the
conditional passive samplers)

5. Model Output – Emissions
Average emissions for each deployment cycle (Oct 2012 – Feb 2013)
 Decrease in volatilization from surface during winter

6. Model Output – Emissions
Histogram (frequency distribution) of output emissions from FIDES
 Skewed distribution, 92% of values fall between 20 – 100 g m-2 s-1

7. Model Output – Emissions
Emissions summary
 Average Emissions: 4.7 g m-2 d-1; 41 g head-1 d-1
 Percent of Fed-Nitrogen emitted as NH3 averaged 53%

8. Conclusions
 Emissions decreased throughout the winter as
volatilization decreased
 Predicted emissions have a skewed distribution
 Average output from the model was 20 – 100 g
m-2 s-1
 Emissions averaged 41 g head-1 d-1 and 4.7 g m-2
d-1
 53% of Fed N emitted to air as NH3

9. References
1. Fdfs
Thank
You!