UNFCCC Inventories of Industrial Processes and Waste
INDUSTRIAL PROCESSES AND PRODUCT USE
The industrial processes and product use (IPPU) sector covers the greenhouse gas emissions resulting from various industrial activities that produce emissions not directly the result of energy consumed during the process and the use of man-made greenhouse gases in products (IPCC, 2006). Examples include the release of CO2 as a by-product of cement production and the use of fossil fuel (primarily natural gas) as a feedstock in ammonia production. The IPPU sector accounts for about 7 percent of total greenhouse gas emissions from Annex I countries (UNFCCC, 2008) and about 6 percent of total greenhouse gas emissions for non-Annex I countries (UNFCCC, 2005).
Carbon dioxide (CO2) is the most important greenhouse gas emitted by the IPPU sector, comprising about 69 percent of total emissions (in terms of CO2 equivalents) from the sector for Annex I countries (UNFCCC, 2005). The main sources of CO2 in this sector are the production of cement, lime, glass, ammonia, iron, steel, and aluminum. The calcination of limestone produces lime, which may then be combined with silica compounds to produce clinker (an ingredient of cement). Both processes result in CO2 emissions. Glass production emits CO2 during the melting and fusion of limestone, dolomite, and soda ash. The principal source of CO2 emissions from ammonia production is the steam reforming of natural gas (methane, CH4) to produce hydrogen (H2). Iron and steel production yields CO2 emissions through the use of metallurgical coke to convert iron ore to pig iron in a blast furnace. Similarly, CO2 is emitted during the smelting process from the use of carbon to reduce alumina to aluminum.
The CO2 emissions from mineral, chemical, and metal production can be estimated simply by applying appropriate emission factors to national-level production data. The major source of uncertainty in emissions from the mineral industry is typically the activity data (IPCC, 2006; EPA, 2008) because the chemistry of the processes involved is known. For cement production, CO2 emissions should ideally be estimated using national-level data on clinker production, the lime content of the clinker, and the fraction of lime from limestone. However, national statistics on cement and/or clinker production may not be complete for countries in which a substantial part of production comes from numerous small kilns, for which data are difficult to obtain. If clinker production data are not available, they are inferred from information on the quantities of cement produced (correcting for imports and exports) and the types and clinker fraction of the cement. For lime and glass production, CO2 emissions can be estimated using national-level data on the types and quantities of lime or glass produced (or, less preferably, total lime or glass production figures) and default emission factors. The key source of uncertainty for lime production is incomplete data; reported lime production statistics often omit nonmarketed lime production, potentially resulting in order-of-magnitude underestimates. For glass production, activity data uncertainties
are magnified where glass production is measured in a variety of units.
In the chemical and metal industries, reliable production data are available for most countries, so the emission factors present the greatest source of uncertainty, particularly for iron and steel production. For ammonia production, CO2 emissions can be estimated using national-level data on ammonia production (or, less preferably, ammonia production capacity) and default values for the quantity of fuel (typically natural gas) required as feedstock per unit of output, the carbon content of the fuel, and the carbon oxidation factor. Any CO2 recovered for purposes of urea production is also accounted for. For iron and steel production, the CO2 emissions are estimated by applying the appropriate emission factors to national statistics on the amount of steel produced by each method and the total amount of pig iron produced that is not processed into steel. Similarly, the estimation of CO2 emissions in aluminum production requires national-level production data by process type (i.e., Søderberg or Prebake) to which the appropriate default emission factor can then be applied.
Hydrofluorocarbons (HFCs) comprise about 18 percent of total emissions (in terms of CO2 equivalents) from the IPPU sector for Annex I countries.1 The use of HFCs as substitutes for ozone-depleting substances in a variety of industrial applications is by far the largest source of HFC emissions, accounting for about 86 percent of total emissions from the sector, and their usage is growing rapidly. A smaller, but significant source of HFC emissions is the generation of trifluoromethane (HFC-23) as a by-product during the production of chlorodifluoromethane (HCFC-22).
Actual emissions of HFCs are estimated using either an emission-factor or a mass-balance approach (IPCC, 2006). Both methods can use activity data collected at either the application level (e.g., refrigeration) or the subapplication level (e.g., equipment or product type); the latter is expected to yield higher-accuracy estimates. For the emission-factor approach, HFC emissions are calculated by determining the net consumption of a chemical in a specific application or subapplication (production plus imports minus exports minus destruction of the chemical) and then applying an emission factor(s) to the net consumption. For the mass-balance approach, emissions are estimated as the sum of the sales of a chemical and, for equipment containing this chemical, the total charge of retired equipment minus the total charge of new equipment. The major source of uncertainty in national estimates of HFC emissions is the lack of activity data on chemical production or sales in countries where suppliers treat the information as confidential. This barrier to the production of reliable national estimates is being reduced with the development of regional and global databases of ozone-depleting substances. For example, databases that track the phase-out of ozone-depleting substances are directly relevant for estimating the phase-in of HFC substitutes (IPCC, 2006).
Emissions of HFC-23 can be calculated by applying a default emission factor to the quantity of HCFC-22 produced. Given the known variability in emissions from different HCFC-22 manufacturing facilities, the uncertainty in the emission factor far outweighs the uncertainty in the activity data (IPCC, 2006).
Emissions of nitrous oxide (N2O) from nitric acid and adipic acid production comprise about 7 percent of total emissions from the IPPU sector in Annex I countries.2 Nitric acid production emits N2O as a byproduct during the catalytic oxidation of ammonia, and adipic acid production (most of which takes place in a few plants in the United States and Europe) generates N2O as a by-product during a process involving the oxidation of nitric acid. Emissions of N2O from both sources can be estimated by multiplying production by a default emission factor. For nitric acid production, the major source of uncertainty in N2O emissions is the activity data. Nitric acid production is often underestimated because nitric acid is formed as part of a larger production process and is never sold on the market. For adipic acid production, neither the default emission factor nor the activity data are significant sources of uncertainty (IPCC, 2006). The default emission factor
is derived from a well-understood chemical reaction (i.e., nitric acid oxidation), and only a small number of adipic acid plants exist.
The waste sector is not a significant source of greenhouse gas emissions, accounting for only about 3 percent of the total from Annex I countries (UNFCCC, 2008) and about 4 percent of the total from non-Annex I countries (UNFCCC, 2005). This sector covers the greenhouse gas emissions from solid waste disposal, biological treatment of solid waste, burning of waste, and wastewater treatment and discharge (IPCC, 2006). Waste sector reporting includes neither the greenhouse gas emissions resulting from the use of waste material as fuel nor the CO2 emissions resulting from the decomposition or burning of organic biomass. These emissions are accounted for under the energy sector and the agriculture, forestry, and other land-use sector, respectively.
The primary greenhouse gas emitted from the waste sector is CH4, which accounts for about 90 percent of the total (in terms of waste sector CO2 equivalents) in Annex I countries.3 The degradation of organic material under anaerobic conditions at solid waste disposal sites (SWDS) is the principal source of CH4 emissions. The potential of SWDS to generate CH4 depends on the degradable organic carbon (DOC) content of the waste, which is a function of the amount and composition of the waste disposed, and on the waste management practices. Methane emissions from SWDS are calculated using the First Order Decay method, which assumes that the rate of CH4 production is directly proportional to the amount of DOC remaining in the waste. The quantity of CH4 that is oxidized in the landfill’s top layer and/or is recovered and combusted is then subtracted from the calculated emissions value.
The key source of uncertainty in estimates of CH4 from SWDS is the activity data relating to the quantities and composition of the waste disposed (several decades of historical data are required), although some of the emission factors can also be highly uncertain. For many countries, data on waste amounts and composition (particularly historical data) are not available and default activity data must be used. The major uncertainties in the emission factors include the DOC values assigned to different waste types (e.g., municipal) and materials (e.g., paper, food), the fraction of DOC that is ultimately degraded and released from SWDS, and the half-life of the DOC, which is difficult to measure in real solid waste disposal sites. Also highly uncertain are the emission factors used to determine the fraction of CH4 that is oxidized in the landfill’s top layer, which depends on whether the SWDS is managed or unmanaged and also varies considerably with conditions at the site.
The other significant source of CH4 emissions within the waste sector is the anaerobic treatment or disposal of wastewater. The CH4 emitted from wastewater handling depends on the amount of degradable organic material, measured by biological oxygen demand in domestic wastewater and chemical oxygen demand in industrial wastewater. The Intergovernmental Panel on Climate Change (IPCC) provides a means of estimating the quantity of domestic wastewater generated as well as default values for biological oxygen demand for selected regions and countries. Similarly, the IPCC provides default values for quantities of industrial wastewater generated and the chemical oxygen demand for various industry types. Reliable estimates of the quantity of CH4 released from wastewater discharge are particularly difficult to obtain for developing countries due to uncertainties in the fraction of domestic wastewater that is removed by sewers (as opposed to being treated in latrines), the fraction of sewers that are open, and the degree to which these open sewers are anaerobic (IPCC, 2006).
Carbon dioxide is a relatively minor source of greenhouse gas emissions from the waste sector, accounting for about 4 percent of total emissions (in terms of CO2 equivalents) from the sector for Annex I Parties.4 The predominant source of these emissions,
comprising about 97 percent of total CO2 emissions from this sector, is the incineration and open burning of waste containing fossil carbon (e.g., plastics, certain textiles). The practice of waste incineration is currently more common in developed countries, while open burning of waste occurs predominantly in the developing world. However, the basic approach recommended by the IPCC for estimating CO2 emissions from these two sources is the same: the quantity of waste incinerated and/or open-burned is multiplied by default values for the dry matter content, total carbon content, fossil carbon fraction, and oxidation factor for the waste (IPCC, 2006). The major source of uncertainty is the estimation of the fossil carbon fraction of the waste, which is directly related to uncertainties regarding waste composition. Where country-specific data regarding quantities of waste incinerated and/or open-burned are not available, large uncertainties are also associated with the waste amounts determined from the IPCC default values for waste generation and management.
Nitrous oxide emissions comprise about 6 percent of total emissions (in terms of CO2 equivalents) from the waste sector for Annex I countries.5 The major source, comprising about 82 percent of total N2O emissions from the sector, is wastewater handling. N2O is emitted from the degradation of nitrogen components in the wastewater (e.g., urea, nitrate, protein). Although both wastewater treatment plants and the discharge of effluent into aquatic environments are sources of N2O emissions, the latter is typically a far more significant source. Emissions of N2O from wastewater effluent discharged to aquatic environments are determined using national statistics on population and annual per capita protein consumption to estimate the total amount of nitrogen discharged in wastewater effluent, and a default emission factor for the N2O emitted per unit of wastewater effluent nitrogen content (IPCC, 2006). Large uncertainties are associated with estimates of N2O emissions from wastewater handling, and the major source of uncertainty is the default emission factor for N2O from the effluent.
EPA (Environmental Protection Agency), 2008, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006, EPA 430-R-08-005, Office of Atmospheric Programs, Washington, D.C., available at <http://www.epa.gov/climatechange/emissions/ usgginventory.html>.
IPCC (Intergovernmental Panel on Climate Change), 2006, 2006 IPCC Guidelines for National Greenhouse Gas Inventories, H.S. Eggleston, L. Buendia, K. Miwa, T. Ngara, and K. Tanabe, eds., prepared by the National Greenhouse Gas Inventories Programme, Institute for Global Environmental Strategies, Hayama, Kanagawa, Japan, 5 volumes.
UNFCCC (United Nations Framework Convention on Climate Change), 2005, Sixth compilation and synthesis of initial national communications from Parties not included in Annex I to the Convention, prepared by the UNFCCC Secretariat, October 2005, available at <http://unfccc.int/ghg_data/ghg_data_unfccc/ items/4146.php>.
UNFCCC, 2008, Report on national greenhouse gas inventory data from Parties included in Annex I to the Convention for the period 1990-2006, prepared by the UNFCCC Secretariat, November 2008, available at <http://unfccc.int/ghg_data/ghg_ data_unfccc/items/4146.php>.