1. AARHUS UNIVERSITY NH 3 Emissions from Fertilisers Nick Hutchings, Aarhus University J Webb, Ricardo-AEA 1

2. AARHUS UNIVERSITY Some history Lack of scientific documentation for the Guidebook methodology Review of literature (AU Environmental Sciences) Mean emission factor for each fertiliser type Some increases in emission factors (especially urea) Additional data found (Bouwman et al 2002 database) More detailed analysis (AU Agroecology + Ricardo-AEA) 2

3. AARHUS UNIVERSITY Statistical analysis Variables considered: Fertiliser type Measurement method Location (indoor, outdoor) Application method (broadcast, incorporated etc) Soil type (clay content) Soil pH Soil CEC Crop type (bare soil, grass, maize, rice, other cereals) Temperature Rainfall intensity (mm/day) 3

4. AARHUS UNIVERSITY Developments since last year We found more data. We wished to distinguish between low- and high-emission, non-urea fertilisers. Germany requested access to the data and undertook their own analysis Detected some potentially duplicate data We investigated and found some were duplicates, some not Provided additional data We included this in the dataset Pointed out that the coefficients describing the rainfall and CEC effect was based on few data (i.e. uncertain) We reassessed some publications and found some additional data Reanalysed the data 4

5. AARHUS UNIVERSITY Results last year Data are unbalanced Many data are missing from individual observations Significant differences between urea (U), fertilisers with urea (U+) and fertilisers without urea (U-) and Significant positive effect of soil pH Significant fertiliser type x soil pH interaction and Significant negative effect of soil CEC and Significant positive effect of temperature and Significant negative effect of rainfall 5

6. AARHUS UNIVERSITY Results this year Data are unbalanced Many data are missing from individual observations Significant differences between urea (U), fertilisers with urea (U+) and fertilisers without urea, low-emission (U-L) and high-emission (U-H) and Significant positive effect of soil pH Significant fertiliser type x soil pH interaction and Significant negative effect of soil CEC and Significant positive effect of temperature or Significant negative effect of rainfall 6

7. AARHUS UNIVERSITY Choice of model Fertiliser type Soil pH Air temperature More accurate data 7 Most of the variance is associated with differences between studies Methodological differences? Encourage and support standardised experiments Choose not to include soil CEC Poorly parameterised, due to lack of data

8. AARHUS UNIVERSITY Parameterisation Normal soil pH (6.5) and alkaline pH (7.5) 8 Need to estimate temperature when fertiliser is applied Data on timing of fertiliser application are not available Need to make assumptions Air temperature 7 Celsius (”spring, all regions”) Air temperature 15 Celsius (”summer grassland, temperate climate”) Air temperature 20 Celsius (”summer grassland, double-cropping, Mediterranean climate”) Fertiliser is usually applied: In the spring (spring and winter arable crops, grassland) In the summer (grassland and double-cropped arable)

9. AARHUS UNIVERSITY Example emissions 9 Norm pH GB 2013 High pH GB 2013 Celsius71520 71520 Urea1720212419222324 MAP34411891011 AS8991319212327 AN11243334 CAN11121222

10. AARHUS UNIVERSITY New model versus old model Lower emissions than Guidebook 2013 Higher emissions than in revised chapter, sent for open review 10

11. AARHUS UNIVERSITY Tier 2 methodology in practice Divide land area between agro-ecological (temperature) zones (AEZ) Partition each AEZ into areas with soil pH >7 and pH ≤ 7 Partition each AEZ x soil pH area into arable and grassland/double cropping For each fertiliser type, partition the national amount used between the different AEZ x soil pH x cropping If no data, do so in proportion to their contribution to the total land area. Use the emission factor for each fertiliser type x AEZ x soil pH x cropping to calculate the ammonia emission Sum the ammonia emissions from each fertiliser type x AEZ x soil pH x cropping combination to calculate the total emission 11

12. AARHUS UNIVERSITY Still to do Establish AEZs Re-write the relevant parts of 3D. 12