IAQM Discussion Meeting: How can we tackle the urgent problem of ammonia emissions?

1. Ammonia: principles into practice
19 June 2019
Dr Jeremy Wiltshire

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From Defra 2018: Code of Good Agricultural Practice (COGAP) for Reducing Ammonia Emissions
Why does ammonia emission matter?

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Agriculture emits around
87%
of ammonia from the UK
Latest data for 2017

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• The UK has agreed ammonia emission limits under the 1999 Gothenburg Protocol
• The UK estimates and reports ammonia emissions annually
Policy context

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Agricultural sources (ref: Inventory of Ammonia Emissions from UK Agriculture, 2017)
Beef cattle
24%
Dairy cattle
23%
Poultry
15%
Pigs
8%
Sheep
4%
Horses
1%
Fertiliser
application
18%
Digestate
application
5%
Sewage sludge
application
2%

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Agricultural sources (ref: Inventory of Ammonia Emissions from UK Agriculture, 2017)
Housing
27%
Manure
application
25%
Fertiliser
application
18%
Manure
storage
9%
Grazing/
outdoors
7%
Hard
standings
7%
Digestate
application
5%
Sewage sludge
application
2%

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Ammoniacal N content of manures
Exposure to air
• Grazing vs housing
• Spreading management and environment
Filtration
pH
Urea fertiliser breakdown (hydrolysis)
Principles governing emission and mitigation

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• Manures contain ammoniacal nitrogen, which is ‘available’ for emission to air
• N content (and NH3 content) of manures can be influenced by diet
• Decreases in protein content and change in amino acid balance leads to important
decreases in ammonia emissions
• Ammoniacal N content of manures affects emission throughout the manure handling
chain
Ammoniacal N content of manures

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Manure:
• mix of faeces and urine (plus bedding)
• Contains ammoniacal N
• Moves from housing to storage to spreading
N ‘flows’ through the system, from housing to storage to spreading
Relevance to mitigation:
• If N is ‘saved’ in storage, more flows through to spreading, so more is available to be
lost at spreading
N-flow concept in housed livestock systems
Housing
27%
Manure
application
25%
Fertiliser
application
18%
Manure
storage
9%
Grazing/
outdoors
7%
Hard
standings
7%
Digestate
application
5%
Sewage sludge
application
2%

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From Misselbrook et al, 2008: Ammonia Mitigation User Manual

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• Minimising exposure to air
minimises emission
• Most exposure to air happens
in housing and at spreading
• Minimise housing
Exposure of manures to air

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• Spreading techniques can reduce exposure to air
• Around 40% of the readily available nitrogen content of manures is often lost following
surface application to land
• Windspeed and temperature are important factors
• Time from spreading to incorporation is important
Exposure of manures to air

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Source: Defra 2018. Code of Good Agricultural Practice (COGAP) for Reducing Ammonia Emissions.
https://www.gov.uk/government/publications/code-of-good-agricultural-practice-for-reducing-ammonia-emissions
Exposure of manures to air

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• Reduced emission spreading techniques
Source: Defra 2018. Code of Good Agricultural Practice (COGAP) for Reducing Ammonia Emissions.
https://www.gov.uk/government/publications/code-of-good-agricultural-practice-for-reducing-ammonia-emissions
Exposure of manures to air

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• Capture /filter at point of emission from
buildings
• Only possible in buildings with forced
ventilation – pigs and poultry
Potential for filtration

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• Decreasing the pH
from (e.g.) 7.5 to 5.5
shifts the balance
between NH3 and NH4
+
• Acidification is used in
Denmark and interest
in the UK is increasing
• Relatively expensive
• Abatement 40-50%
overall depending on
pH reduction
pH of manures

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• Urease enzymes catalyse the hydrolysis of urea
• urea + water ammonia + carbon dioxide
• Per kg fertilizer N ammonia emissions are reduced by c. 80% by using ammonium
nitrate instead of urea
• This is among the most cost-effective means of reducing ammonia emissions
• Urease inhibitors can be added to urea - reduces ammonia emissions by 70%
Urea hydrolysis

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Uptake potential is difficult to estimate
• Uptake depends on policy and economic drivers
• Further uptake depends on extent of current implementation
Uptake of most mitigation actions is limited by cost to the farmer
Uptake of some mitigation actions is limited by practical considerations
• Covering solid manure stores
• Covering some slurry stores
How long does it take to implement mitigation actions?
Practicalities in the farming industry

19. Contact: Jeremy Wiltshire
Email: jeremy.wiltshire@ricardo.com
Direct Dial: +44 (0)1235 753 593
Mobile: +44 (0)7968 707 699
Reception: +44 (0)1235 753 000