7 Precursors and Indirect Emissions

7.1 Introduction 7.4

7.2 Precursor emissions 7.4

7.2.1 Inventory of precursors 7.5

7.2.2 Link to relevant methodology chapters in the EMEP/CORINAIR Emission Inventory Guidebook 7.7

7.3 Indirect N2O emissions from the atmospheric deposition of nitrogen in NOx and NH3 7.15

7.3.1 Methodology 7.15

7.3.2 Quality Assurance/Quality Control, Reporting and Documentation 7.16

References 7.16


Equation 7.1 N2O emissions from atmospheric deposition of NOx and NH3 7.15


Table 7.1 Link between the IPCC categories and the corresponding methodology chapters in

EMEP/CORINAIR Guidebook 7.7


Box 7.1 CLRTAP and Emission Inventory Guidebook 7.5

Box 7.2 Calculating CO2 inputs to the atmosphere from emissions of carbon-containing compounds 7.6



Although they are not included in global warming potential-weighted greenhouse gas emission totals, emissions of carbon monoxide (CO), oxides of nitrogen (NOx), non-methane volatile organic compounds (NMVOCs), and sulphur dioxide (SO2) are reported in greenhouse gas inventories. Carbon monoxide (CO), Nitrogen oxides (NOx) and NMVOC in the presence of sunlight contribute to the formation of the greenhouse gas ozone (O3) in the troposphere and are therefore often called 'ozone precursors'. Furthermore, NOx emission plays an important role in the earth's nitrogen cycle. Sulphur Dioxide emissions lead to formation of sulphate particles, which also play a role in climate change. Ammonia (NH3) is an aerosol precursor, but is less important for aerosol formation than SO2.

Section 7.2 addresses the estimation and reporting of the precursors for national inventories. The methodologies for ambient air quality emission inventories have been elaborated in detail in the EMEPVCORINAIR Emission Inventory Guidebook (Guidebook), and these methodologies for CO, NOx, NMVOCs, and SO2 emissions are referenced in this chapter rather than to be included in the 2006IPCC Guidelines for National Greenhouse Gas Inventories (2006 Guidelines). Exceptions are for sources not well-covered by the Guidebook.

Section 7.3 addresses nitrous oxide (N2O) emissions that result from the deposition of the nitrogen emitted as NOx and NH3. Nitrous oxide is produced in soils through the biological processes of nitrification and denitrification. Simply defined, nitrification is the aerobic microbial oxidation of ammonium to nitrate and denitrification is the anaerobic microbial reduction of nitrate to nitrogen gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of denitrification and a by-product of nitrification that leaks from microbial cells into the soil atmosphere. One of the main controlling factors in this reaction is the availability of inorganic nitrogen in the soil and therefore deposition of nitrogen resulting from NOx and ammonia (NH3) will enhance emissions. N2O emissions will also be enhanced if nitrogen is deposited in the ocean or in lakes. For this reason the 2006 Guidelines include guidance for estimating N2O emissions resulting from nitrogen deposition of all anthropogenic sources of NOx and NH3. Only agricultural sources of nitrogen were considered in the Revised 1996 Guidelines (IPCC, 1997).

Guidance is provided in Section 7.3 on estimating N2O emissions from atmospheric deposition resulting from all categories except agricultural soil management and manure management. Section 7.3 provides information on NOx emissions. Countries may use national methodologies to estimate emissions of NH3 not originating from agriculture. NH3 emissions are also covered in the EMEP/CORINAIR Emission Inventory Guidebook.


Where the country already has inventories for precursors, the results should be reported in the inventory. In some countries, air pollutant emission inventories are collected via separate procedures than the inventory of direct greenhouse gases, and the methods to produce these inventories can differ from those for greenhouse gases. Also, while the greenhouse gas emissions and sinks inventories are often based on national statistics, air pollutant emission inventories are often developed using plant specific data. Countries should consider whether there is any scope for improving consistency between inventories or cross-checking estimates.

Detailed methodologies for estimating the emissions of precursors are provided in the EMEP/CORINAIR Emission Inventory Guidebook ( This guidebook has been developed for emission inventories of substances regulated under the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP) (see Box 7.1) and covers all source sectors and should therefore be considered as primary source of information for estimation of these emissions.

Table 7.1 provides a linkage between the IPCC categories and the corresponding methodology chapters in the

EMEP/CORINAIR Guidebook. This table provides information on the specific EMEP/CORINAIR chapters that list

methodologies for preparing NOx, CO, NMVOCs, NH3 and SO2 inventories. It also includes information on the availability of methods and the significant precursor emissions from particular categories.

Some of the methodologies and emission factors in the EMEP/CORINAIR Guidebook are technology-specific and are relevant to conditions and categories in both developed and developing countries. However, for some

1 Cooperative programme for the monitoring and evaluation of the long-range transmission of air pollutants in Europe (EMEP).

2 The EMEP/CORINAIR Nomenclature for Reporting (NFR) source categories have been developed to be compatible to the IPCC reporting categories.

sectors, like solvents, small combustion sources (biomass in particular) and open burning, differences between the developed and developing countries may be larger, and the EMEP/CORINAIR Guidebook should be used with great care.

Box 7.1

CLRTAP and Emission Inventory Guidebook The Convention on Long-Range Transboundary Air Pollution has been in force since 1979 and includes eight protocols with requirements to reduce emissions and technical annexes on abatement techniques. More detailed information on the Convention is available at As emissions of oxides of nitrogen (NOx), carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs), and sulphur dioxide (SO2) are reported both to the UNFCCC and UNECE CLRTAP it is important to ensure consistent methodologies and reporting between these two Conventions. (UNECE, 2003)

The EMEP/CORINAIR Guidebook has been prepared by the LRTAP Task Force on Emission Inventories and Projections (TFEIP) and is updated regularly by the Expert Panels under the TFEIP ( to provide comprehensive information and methodologies for estimating emissions. The EMEP/CORINAIR Emission Inventory Guidebook is published by the European Environment Agency (EEA).

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