COMPLETENESS Tier 1
Tier 1 inventories are complete if emissions are computed based on a full accounting of all limestone and dolomite applied to soils. Carbonate lime usage statistics provide the most direct inference on applications to soils. However, sales records or mining data combined with import/export and industrial processing records provide sufficient information to approximate the amount of lime applied to soils. If current data are not sufficient due to incomplete records, it is good practice to gather additional data for future inventory reporting, particularly if liming C emissions are a key source category.
Completeness in Tier 2 inventories is dependent on the adequacy of the activity data (see Tier 1), but will also depend on additional country-specific data that were used to refine emission factors. This may include the availability of data about the purity of lime and/or site-level and hydrological data to better specify emission factors relating the amount of CO2 released per amount of C added to soils in carbonate lime.
Beyond the considerations for Tier 1 and 2, completeness of Tier 3 inventories is also dependent on the data needs and representativeness of the measurement design and/or modelling framework. Inventory compilers should review their approach and determine if the advanced estimation system are adequate to address the net release of CO2 from carbonate limes applied to soils. If gaps or limitations are identified, it is good practice to gather additional data so that the fate of liming carbonates is fully addressed by the Tier 3 method.
TIME SERIES CONSISTENCY
The same activity data and emissions factors should be applied across the entire time series for consistency. At the Tier 1 level, default emission factors are used so consistency is not an issue for this component. However, the basis for the activity data may change if new data are gathered, such as a statistical survey compiling information on applications to soils versus older activity data relying strictly on mining and import/export records. While it is good practice for the same data protocols and procedures to be used across the entire time series, in some cases this may not be possible, and inventory compilers should determine the influence of changing data sources on the trends. Guidance on recalculation for these circumstances is presented in Volume 1, Chapter 5.
Consistency in activity data records across the time series is important for Tier 2 inventories (see Tier 1). In addition, new factors that are developed based on country-specific data should also be applied across the entire time series. In rare cases when this is not possible, inventory compilers should determine the influence of changing emission factors on the trends; additional guidance on recalculation for these circumstances can be found in Volume 1, Chapter 5.
Similar to Tier 2, it is good practice to apply the country-specific estimation system throughout the entire time series; inventory agencies should use the same measurement protocols (sampling strategy, method, etc.) and/or model-based system throughout the inventory time period.
QUALITY ASSURANCE/QUALITY CONTROL Tier 1
It is good practice to implement Quality Assurance/Quality Controls with internal and independent reviews of inventory data and results, ensuring: 1) activity data have been processed appropriately to estimate application to soils; 2) activity data have been properly transcribed into the worksheets or inventory computation software; and 3) emission factors have been assigned appropriately.
Internal reviews should be conducted by the inventory compiler(s), and may involve visual inspection as well as built-in program functions to check data entry and results. Independent reviews are conducted by other agencies, experts or groups who are not directly involved with the compilation. These reviews need to consider the validity of the inventory approach, thoroughness of inventory documentation, methods explanation and overall transparency.
In addition to the Quality Assurance/Quality Control measures under Tier 1, the inventory compiler should review the country-specific emission factors for Tier 2 inventories. If using factors based on direct measurements, the inventory compiler should review the measurements to ensure that they are representative of the actual range of environmental conditions. If accessible, it is good practice to compare the country-specific factors with Tier 2 emission factors used by other countries with comparable circumstances, in addition to the IPCC defaults. Given the complexity of inorganic C transformation, specialists in the field should be involved in the review process to provide an independent critique of the emission factors.
Country-specific inventory systems will likely need additional Quality Assurance/Quality Control measures, but this will be dependent on the systems that are developed. It is good practice to develop a Quality Assurance/Quality Control protocol that is specific to the country's advanced estimation system, archive the reports, and include summary results in reporting documentation.
REPORTING AND DOCUMENTATION
For Tier 1, inventory compilers should document trends and uncertainties in carbon lime applications to soils and relate those patterns to the CO2 emission trends. Significant fluctuations in annual emissions across the time series should be explained.
It is good practice to archive actual databases, such as mining records or usage statistics from surveys, and procedures used to process the data (e.g., statistical programs). The worksheets or inventory software, which was used to estimate emissions, should be archived along with input/output files that were generated to produce the results.
In cases where activity data are not available directly from databases or multiple data sets were combined, the information, assumptions and procedures that were used to derive the activity data should be described. This documentation should include the frequency of data collection and estimation, and uncertainty. Use of expert knowledge should be documented and correspondences archived.
In addition to the considerations for Tier 1, inventory compilers should document the underlying basis for country-specific emission factors, as well as archive metadata and data sources used to estimate country-specific values. Reporting documentation should include the new factors (i.e., means and uncertainties), and it is good practice to include a discussion in the inventory report about differences between these values and default factors or country-specific factors from regions with similar circumstances to those of the reporting country.
When discussing trends in emissions and removals from year to year, a distinction should be made between changes in activity levels and changes in methods, including emission factors, and the reasons for these changes need to be documented.
Tier 3 inventories need similar documentation about activity data and emission/removal trends as lower tier approaches, but additional documentation should be included to explain the underlying basis and framework of country-specific estimation systems. With measurement-based inventories, it is good practice to document the sampling design, laboratory procedures and data analysis techniques. Measurement data should be archived, along with results from data analyses. For Tier 3 approaches using modelling, it is good practice to document the model version and provide a model description, as well as permanently archive copies of all model input files, source code and executable programs.
Adding urea to soils during fertilisation leads to a loss of CO2 that was fixed in the industrial production process. Urea (CO(NH2)2) is converted into ammonium (NH4+), hydroxyl ion (OH-), and bicarbonate (HCO3-), in the presence of water and urease enzymes. Similar to the soil reaction following addition of lime, bicarbonate that is formed evolves into CO2 and water. This source category is included because the CO2 removal from the atmosphere during urea manufacturing is estimated in the Industrial Processes and Product Use Sector (IPPU Sector).
Inventories can be developed using Tier 1, 2 or 3 approaches, with each successive Tier requiring more detail and resources than the previous. It is good practice for countries to use higher tiers if CO2 emissions from urea are a key source category.
11.4.1 Choice of method
A decision tree is provided in Figure 11.5 to assist inventory compilers with selection of the appropriate tier. Tier 1
CO2 emissions from urea fertilisation can be estimated with Equation 11.13:
CO2-C Emission = annual C emissions from urea application, tonnes C yr-1 M = annual amount of urea fertilisation, tonnes urea yr-1 EF = emission factor, tonne of C (tonne of urea)-1
Procedural Steps for Calculations
The steps for estimating CO2-C emissions from urea applications are:
Step 1: Estimate the total amount of urea applied annually to a soil in the country (M).
Step 2: Apply an overall emission factor (EF) of 0.20 for urea, which is equivalent to the carbon content of urea on an atomic weight basis (20% for CO(NH2)2). A default -50% uncertainty may be applied (Note: uncertainties can not exceed the default emission factor because this value represents the absolute maximum emissions associated with urea fertilization).
Step 3: Estimate the total CO2-C emission based on the product of the amount of urea applied and the emission factor.
Multiply by 44/12 to convert CO2-C emissions into CO2. Urea is often applied in combination with other nitrogenous fertilizers, particularly in solutions, and it will be necessary to estimate the proportion of urea in the fertilizer solution for M. If the proportion is not known, it is considered good practice to assume that the entire solution is urea, rather than potentially under-estimating emissions for this sub-category.
Tier 2 inventories also use Equation 11.13 and procedural steps, which were provided in the Tier 1 approach, but incorporate country-specific information to estimate emission factors.
CO2 emissions from urea applications could be estimated with more detailed models or measurements that incorporate the possibility of bicarbonate leaching to deep groundwater, and/or lakes and oceans, and thus not contributing to CO2 emissions, at least not immediately. Note that increases in soil inorganic C from urea fertilization do not represent a net removal of CO2 from the atmosphere. The removal is estimated in the IPPU Sector (Volume 3), and the computations for soils only provide estimates of the amount of emissions associated with this practice. See the Tier 3 section for soil inorganic C in Chapter 2 for additional discussion (Section 2.3.3 on Change in Soil C Stocks).
Figure 11.5 Decision tree for identification of appropriate tier to estimate CO2 emissions from urea fertilisation
Figure 11.5 Decision tree for identification of appropriate tier to estimate CO2 emissions from urea fertilisation
1: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.
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