Techniques for measuring ammonia emissions from land applications of manure and fertiliser

1. NADP Ammonia Workshop, Washington DC, 22-24 October 2003 Techniques for measuring ammonia emissions from land applications of manure and fertiliser Tom Misselbrook and Fiona Nicholson Institute of Grassland and Environmental Research, North Wyke

2. Structure of presentation • Techniques available • Micrometeorological • Enclosure • Samplers for measuring concentration (or flux) • Most commonly-used methodologies • Micrometeorological mass balance • Wind tunnels • Equilibrium concentration technique • Conclusions

3. Techniques available • Soil N balance, 15N Micrometeorological techniques Mass balance Eddy correlation Gradient methods Backward Lagrangian stochastic model Equilibrium concentration technique Enclosure techniques Static chambers Dynamic chambers Controlled release ratio techniques

4. Micrometeorological techniques Mass balance – Integrated Horizontal Flux upwind mast downwind mast wind direction horizontal NH3 flux vertical NH3 flux manure-treated surface x Flux from treated area = (IHFdw - IHFuw) / x

5. Micrometeorological Mass Balance (IHF) technique Passive flux samplers mounted on a mast

6. Micrometeorological techniques Mass balance – other methods Theoretical profile shape – measure flux at 1 predetermined height (Zinst) TPS Philip’s solution – flux derived from measured concentration profile and theoretically calculated concentration profile for unit flux Perimeter profile method – measure inward and outward fluxes at several heights around the perimeter of a treated circular plot

7. Micrometeorological techniques Eddy correlation w’ – fluctuation in vertical wind speed (sonic anemometer) x’ - deviation from mean concentration (TDL) Relaxed eddy accumulation b – empirical constant sw–standard deviation in vertical wind x+ - mean concentration, updraft x- - mean concentration, downdraft Sonic anemometer Wet chemistry (e.g. denuder)

8. Micrometeorological techniques Gradient methods Measure concentration, wind speed and temperature at 2 or more heights Constant flux layer Flux = K dX/dz fetch:height 100:1

9. Micrometeorological techniques Backward Lagrangian stochastic model u is windspeed, c is ammonia concentration n is a constant Flux = uc/n Software commercially available At it’s simplest, requires measurement of windspeed and concentration at only 1 height

10. Equilibrium concentration technique Flux = (Ceq - Ca,z) Kz,a

11. Enclosure techniques Static chambers Concentration Time

12. Enclosure techniques Dynamic chambers – wind tunnels Flux = V (Cout - Cin) / A

13. Controlled Release Ratio technique Cb Cs Cp Fluxp = f (Cp - Cb) where f = Fluxs/(Cs-Cb)

14. Samplers • Laser/optical instruments - TDL, DOAS, FTIR

15. Laser/optical Instruments • Advantages: • very sensitive • fast response (real-time results) • Disadvantages: • cost • require power

16. Samplers • Optical absorption samplers - TDL, DOAS, FTIR • Absorption flasks

17. Absorption flasks • Advantages: • inexpensive • simple • can be used for a wide concentration range • Disadvantages: • require power • time-averaged concentration measurements • freezing/evaporation problems

18. Samplers • Optical absorption samplers - TDL, DOAS, FTIR • Absorption flasks • Denuders • Filters/badges

19. Filters/badges • Advantages: • inexpensive • simple • no power requirement • Disadvantages: • labour intensive • time-averaged concentration measurements • difficulty in estimating required exposure times

20. Samplers • Optical absorption samplers - TDL, DOAS, FTIR • Absorption flasks • Denuders • Filters/badges • Passive flux samplers

21. Passive flux samplers – “shuttles” • Advantages: • direct measurement of flux • no power requirement • simple • Disadvantages: • cost? ($300-400 each) • time-averaged flux measurement

22. Sampler inter-comparison tests • Concentration range 80 – 7,500 ug N m-3 • Exposure time 1 – 6 hours • Absorption flasks – 2 in series • acid concentration (0.1, 0.01, 0.001M) • air flow rate (0.6 – 3.5 l min-1) • end type (scintered glass, open) • Badges • Shuttles • angle if incidence of air flow (20o, 40o)

23. Sampler inter-comparison tests • Absorption flasks • Mean capture in 1st flask 97% • No sig. effect of acid strength • No sig. effect of air flow rate • No sig. effect of end type • Shuttles • No sig. effect of angle of incidence

24. Sampler inter-comparison tests Shuttles vs. absorption flasks

25. Sampler inter-comparison tests Badge vs. absorption flasks

26. Sampler inter-comparison tests Sampler repeatability

27. Sampler inter-comparison tests ‘Blank’ values and detection limits (ug N)

28. Technique inter-comparisons ECT Circular manure-treated plot 3 replicate plots 4 experiments (different manure types) MB IHF Wind tunnels

29. Technique inter-comparisons

30. Technique inter-comparisons Coefficients of variation (%) in measured emission rates * many missing data

31. Choice of technique IHFWind tunnelsECT type of study absolute comparative comparative ease of replication * *** *** land area required *** * * capital cost * *** * labour costs * ** *** practicality * * ** variability ** ** ** overall reliability *** ** * * low, ** medium, *** high

32. Conclusions • Large number of techniques available • Overall methodology • Sampling concentration/flux • CV of measurement techniques lowest for MB-IHF • CV of measurements lower for slurries than solid manures • Choice of technique depends on purpose and resources available • Still room for the development of a non-intrusive small plot technique