This is part II of a blog series - A Primer on 2006 IPCC Guidelines for Emission Inventories. 

In this post we talk about Volume I of the 2006 IPCC guidelines which describes  how to collect, process and report emission data.  

Data Collection 

Data collection is one of the elemental components of developing a GHG inventory. This includes gathering existing data, generating or measuring new data and adapting the data for its use in the inventory. Now, what is this data? Data or specifically, activity data is the quantitative measure of the level of activity that causes GHG emissions. In simpler terms, the measurable amount of an activity that caused GHG emissions. Some examples are - tonnes of waste sent to a landfill, number of cattle, kilometres driven by two-wheelers, volume of LPG used and so on. This data is measured and reported on an annual basis. 

Generally, there is some data available from various reliable sources such as government departments, research institutes, national statistical or audit agencies etc. In cases when data isn't available, it is advisable to measure or generate data through measurement of the activity. This may include surveys or census. However, in a vast country like India, this may seem unfeasible, given the differences in activity across different regions. Also, it is essential that there is consistency in the time series of the data. In case of data gaps between certain years, the 2006 Guidelines suggest resolving these data gaps through extrapolation or surrogate data based on the trends.  

Once the activity data is procured, it is adapted to fit the GHG inventory framework. In other words, the emissions are then calculated using a simple equation. 

GHG Emissions = Activity Data ✕ Emission Factor

Through this equation, the activity data is converted to emissions data by multiplying it to an emission factor for each greenhouse gas emitted. The emission factor is dependent on various determinants and can be calculated considering them. Based on the fuel combusted or the technology used for combustion, the emission factor changes. The IPCC has provided default values as emission factors for each of the greenhouse gases. However, IPCC recommends that each country calculate their own emission factors based on country specific values for these determinants. 

Key Category Analysis 

After data is collected, it is disaggregated into different categories based on the emission sources and sinks. IPCC has categorised all the emission sources and sinks into five sectors; 

(1) Energy 

(2) Industrial Processes and Product Use (IPPU) 

(3) Agriculture, Forestry and Other Land Use (AFOLU) 

(4) Waste 

(5) Others.  

There are subcategories under these sectors which are differentiated based on factors like fuel combustion activity, industrial material production, technological differences and so on. Every gas emitted from each of these categories is recommended to be calculated separately. As an example, during transportation, CO2, CH4 and N2O are emitted and therefore all three gases should be analysed separately. In some cases, certain gases can be aggregated into one single category, eg., all species of hydrofluorocarbons. 

Once such analysis is completed, it is essential to identify the key categories. Key categories are those sectors and subcategories that have the highest contribution to the national GHG inventory. 

There are two approaches mentioned in the 2006 Guidelines; Approach 1 - identification of the categories that influence the level and trend of the national GHG inventory and Approach 2 - identification of the key categories based on uncertainty analysis. 

Uncertainty Assessment

Uncertainty in emissions inventory are the errors that may occur during data collection either due to systemic errors or random errors. Uncertainties, therefore,  depend on the quality and availability of sufficient data to estimate emissions, or on the ability to measure emissions and properly account for their variability. The 2006 Guidelines instructs how to quantify uncertainties and report it in the national emission inventory. 

After the uncertainty analysis is complete, the emissions data can then be documented in a framework developed by 2006 Guidelines. This framework includes reporting tables and additional documentation in a standard format to ensure consistency in reporting between countries, categories and years. 

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