Archived: Air Pollutant Emission Inventory report: chapter 3

Chapter 3 – Key components of the Air Pollutant Emission Inventory

The Air Pollutant Emission Inventory (APEI) is a comprehensive and detailed inventory of air pollutant emissions in Canada, developed using two types of information:

• facility-reported data, consisting of emissions from relatively large industrial, commercial and institutional facilities
• in-house estimates, including diffuse sources and other sources that are too numerous to be accounted for individually, such as road and non-road vehicles, agricultural activities, construction and solvent use

The APEI is developed using many sources of information, procedures and emission estimation models. Emissions data reported by individual facilities to ECCC’s National Pollutant Release Inventory (NPRI) are supplemented with documented, science-based estimation tools to quantify total emissions. Together, these data sources provide a comprehensive overview of pollutant emissions across Canada.

A compilation framework has been developed that makes use of the best available data, while ensuring that there is no double-counting or omissions. Additional information on the inventory compilation process is provided in Annex 2.

3.1 Facility-reported emissions data

Facility-reported emissions data generally refers to any stationary sources that emit pollutants through stacks or other equipment at specific locations. The major source of facility-reported data is the National Pollutant Release Inventory (NPRI), Canada’s legislated, publicly accessible inventory of pollutant releases (to air, water and land), disposals and transfers for recycling. The NPRI has provided facility-reported data on the 17 pollutants included in the APEI, for more than 6,000 industrial and commercial facilities since 2002 and for heavy metals and persistent organic pollutants since 1994. Prior to 2002, facility-level emissions for the criteria air contaminants were collected and compiled by provincial, territorial and regional environmental authorities across Canada, and provided to Environment and Climate Change Canada for compilation of the APEI.

Facility-reported data from the NPRI are used in the APEI without modifications, except when data quality issues are detected and not addressed during the quality control exercise. The NPRI reporting requirements and thresholds vary by pollutant and, in some cases, by industry. Details on these reporting requirements and thresholds are available on Environment and Climate Change Canada’s website at National Pollutant Release Inventory.

A distinction has been made between reporting facilities and non-reporting facilities. Reporting facilities meet the threshold required to report to the NPRI; while non-reporting facilities do not meet these thresholds due to their size or emission levels, and therefore are not required to report to the NPRI. Some facilities may be required to report emissions on only certain pollutants. Therefore, emissions from the non-reporting facilities or of non-reported pollutants must be estimated in-house to ensure complete coverage. 

3.2 In-house emission estimates

In-house estimates are calculated with information such as production data and activity data, using various estimation methodologies and emission models. These emission estimates are at the national level rather than at any specific geographic locations. These include emissions from non-industrial, residential, commercial, transportation, and other sources, such as open burning, agricultural activities and construction operations. The APEI uses in-house estimates for the following emission sources:

• any residential, governmental, institutional, or commercial operation that does not report to the NPRI
• on-site solid waste disposal facilities
• motor vehicles, aircraft, vessels or other transportation equipment or devices
• other sources, such as open burning, agricultural activities and construction operations

In general, in-house emission estimates are calculated from activity data and emission factors.^{Footnote 1}  Activity data usually comprise statistical production or process data at the provincial, territorial or national level. This information is typically provided by provincial/territorial agencies federal government departments, industry associations, etc. For each source category, activity data are combined with emission factors to produce provincial/territorial-level emission estimates.

The in-house emission estimate methodologies and emission models used in Canada are often based on those developed by the United States Environmental Protection Agency (U.S. EPA) and are adapted to reflect the Canadian climate, fuels, technologies and practices. Methods used in Canada’s APEI are therefore generally consistent with those used in the United States or those recommended in the emission inventory guidebook (EMEP/EEA 2013).

The APEI reports air pollutant emissions from mobile sources such as on-road vehicles, off-road vehicles and engines. For the current edition of the APEI, an emissions estimation model developed by the U.S. EPA (MOVES) was used (see “on-road vehicles” in Table A2-5 of Annex 2). The emissions for off-road vehicles and engines (such as graders, heavy trucks, outboard motors and lawnmowers) were estimated using the U.S. EPA’s NONROAD emission estimation model (see “off-road vehicles and equipment” in Table A2-5 of Annex 2). The parameters in both models were modified to take into account variations in the Canadian vehicle fleet, emission control technologies, types of fuels, vehicle standards, and types of equipment engines and their application in various industries. The emission estimates for civil and international aviation, railways and navigation are estimated using detailed vehicle movement statistics coupled with fuel consumption, engine information, and emission rates by vehicle types.

3.3 Recalculations

Emission recalculation is an essential practice in the maintenance of an up-to-date air pollutant emission inventory. The APEI is continuously updated with improved estimation methodologies, statistics and more recent and appropriate emission factors. As new information and data become available, previous estimates are updated and recalculated to ensure a consistent and comparable trend in emissions. Recalculations of previously reported emission estimates are common for both in-house estimates and facility-reported emission data. More information on recalculations is provided in Annex 2.

3.4 Reconciliation

In several sectors, such as the upstream petroleum industry, estimation of total emissions involves combining estimates provided by facilities with estimates developed in-house by Environment and Climate Change Canada. To prevent  double counting of emissions and to confirm that  the APEI includes all emissions, a comparison and reconciliation of emission estimates from various sources is performed for each pollutant, industry sector and geographical region, as appropriate. More information on the reconciliation process is provided in Annex 2.

3.5 References

[EMEP/EEA] European Monitoring and Evaluation Programme/European Environment Agency. 2013. EMEP/EEA Air Pollutant Emission Inventory Guidebook 2013. Technical Guidance to Prepare National Emission Inventories. Luxembourg: Publications Office of the European Union. Technical Report No. 12/2013.