Canada's Black Carbon Inventory Report 2020

3 Black carbon inventory development

As mentioned in the introduction, the black carbon inventory is based on the Air Pollutant Emission Inventory (APEI) (Environment and Climate Change Canada (ECCC) 2020). This chapter gives an overview of the black carbon inventory development. For more details on the air pollutant emissions inventory development, refer to chapter 3 of the APEI.

3.1 Black carbon as a fraction of PM2.5

Two important assumptions underlie the present inventory: black carbon is predominantly emitted in PM2.5; and only PM2.5 emissions resulting from combustion contain significant amounts of black carbon. Therefore, the basis for the black carbon inventory is the PM2.5 emitted from combustion processes, multiplied by the BC/PM2.5 fractions specific to each type of source. Although important in some cases, PM2.5 emissions from non-combustion sources, such as dust raised by traffic on paved and unpaved roads or by wind and machinery on open fields or mine sites, are not considered sources of black carbon.

For example, diesel engines have relatively high emission rates of PM2.5 per unit energy, and the fraction of black carbon in these PM2.5 emissions is also relatively high. The majority of diesel fuel in Canada is used for mobile sources, particularly in off-road applications. Other combustion sources with high PM2.5 emissions include solid fuel combustion units, such as coal and wood-fired boilers and wood fireplaces. Industrial sources are generally equipped with highly effective PM2.5 controls on boiler emissions, with PM-control efficiencies often in the 90% range. This is reflected in the lower PM2.5 emissions compared to other sources. In contrast, the smaller and markedly different equipment used for residential wood combustion (fireplaces, wood stoves or furnaces) have poorer PM2.5 control efficiencies than larger units, notwithstanding the different types of fuel and firing practices used for burning firewood. Given their lower efficiency, combined with the lack of treatment of stack gases for many existing residential wood-burning devices, such devices are by far the largest source of combustion-related PM2.5 emissions in Canada. Nonetheless, black carbon emissions from residential wood burning are only one-third that of mobile sources due to a lower BC/PM2.5 fraction for wood devices than for diesel engines.

The dataset that breaks down the PM2.5 emitted from a particular source (e.g. diesel engine emissions) into its different components, including black carbon and organic carbon, is known as a speciation profile. Most speciation profiles contain a fraction for elemental carbon; these fractions are commonly used as a surrogate to quantify black carbon emissions. The current inventory relies primarily on the United States Environmental Protection Agency’s (EPA) SPECIATE database (EPA 2014) to calculate black carbon emissions from compiled combustion PM2.5 emissions. Several PM2.5 speciation profiles are specific to the combustion processes or technologies (e.g. appliance types for residential wood combustion), to the fuel type (e.g. diesel, gasoline, natural gas) or to the application (e.g. natural gas use for electrical power generation).

Where readily available, the PM2.5 emissions data from combustion were used directly with BC/PM2.5 fractions to estimate black carbon emissions. Annex B lists all BC/PM2.5 fractions used in this inventory. Separating combustion from non-combustion sources of PM2.5 remains a challenge in some cases because of a lack of data on activities (i.e. quantity of fuel burned) and on non-combustion sources (e.g. rock dust at a mine). In those cases, separating combustion PM2.5 from non-combustion PM2.5 is done on the basis of expert knowledge of the relevant activities prior to applying BC/PM2.5 fractions.

3.2 Use of facility reported emissions

Only PM2.5 emissions resulting from combustion contain significant amounts of black carbon. In the APEI, PM2.5 emission estimates are calculated using a variety of data sources, notably emission estimates reported by Canadian facilities to the NPRI. For sources that are incompletely covered by PM2.5 estimates reported to the NPRI, PM2.5 emissions are calculated in-house using activity data, statistics and emission factors. For this inventory, emissions from manufacturing, electric power generation as well as ore and mineral industries are estimated using facility data. Upstream Oil and Gas Industry estimates are based on facility-reported data used in combination with the results of independent studies (EC 2014; ECCC 2017; Quadram 2019). Emissions due to agricultural, construction and residential (wood and other) fuel combustion are estimated from data on fuel consumption and combustion technologies. Commercial fuel combustion is estimated using a combination of facility-reported and other data sources.

Stack emissions of PM2.5 reported by facilities form the basis of the black carbon estimation from facility reported data. For each individual stack, the appropriate black carbon speciation factor (or factors) was applied to the combustion related PM2.5 (Annex B). The emissions are then summed at the facility level and aggregated to form the sectoral emission estimate.

3.3 Recalculations

As new data and methodologies become available, emission estimates from previous inventory editions are recalculated. Table 2–9 presents the main improvements to the estimation methodologies for this year's inventory.

Table 2-9: Summary of methodological changes, refinement or improvements
Description Impact on emissions
Ore and Mineral Industries

As an improvement to the inventory, the sectors of Iron and steel, and iron ore pelletization were added for completeness. The methodology for determining the portion of combustion PM2.5 remained consistent with other sectors. The appropriate speciation factors were chosen based on technology and are detailed in Table B.1 of Annex B.

The addition of the new sectors increased the overall black carbon emissions from a minimum of 154 tonnes (0.4% of national total) in 2016 and a maximum of 205 tonnes (0.5% of national total) in 2018.
Upstream Oil and Gas Industry

In March 2019, Quadram Engineering Ltd completed a contract to develop a black carbon inventory for flaring in Alberta’s Upstream Oil and Gas (UOG) industry. This study leveraged parallel work under the NSERC FlareNet Strategic Network that involved direct field measurements of black carbon emissions from flares in Alberta and internationally, and controlled laboratory studies. By combining the FlareNet measurement work with available production data from Alberta and detailed gas composition data, Quadram was able to produce a black carbon inventory differentiated by industry segment (e.g. light/medium crude oil production, heavy crude oil cold production, in-situ oil sands production, gas gathering, gas production and well testing) for Alberta. Additionally, they were able to calculate black carbon emission factors by industry segment per volume of flared gas to be used to estimate emissions for other jurisdictions.

The incorporation of the results from this study resulted in recalculations to black carbon emissions from flaring in BC, Alberta, Saskatchewan and Newfoundland and Labrador. Emissions for these four provinces were estimated using emission factors per volume of flared gas by industry segment and the emission factors from Quadram (2019).

The recalculations associated with these methodological changes and updates to reported data resulted in decreases across the entire time series for the Upstream Oil and Gas sector, from a minimum of 353 tonnes (9%) in 2013 to a maximum of 654 tonnes (17%) in 2017. Emissions also decreased by 414 tonnes (11%) in 2014, 486 tonnes (14%) in 2015, and 474 tonnes (14%) in 2016.

Recalculations occurred in the Pulp and Paper Industry sector and Wood Products sector due to reassignment of facility-reported emissions among these two sectors.

Changes to Manufacturing are an increase of 18 tonnes (4%) in 2013, an increase of 13 tonnes (3%) in 2014, an increase of 12 tonnes (3%) in 2015, an increase of 7 tonnes (2%) in 2016, and an increase of 7 tonnes (2%) in 2017, due to reassignment of facility-reported emissions among the Pulp and Paper Industry sector and Wood Products sector.
Transportation and Mobile Equipment

Recalculations occurred in the marine transportation and the air transportation sectors. Provincial marine estimates were redeveloped based on port origin/destination pairs. For air transportation, civil emissions from the cruise segment of each flight were removed from the report total in order to conform with the national total reported in the NFR table.

The marine recalculations will only impact the emissions of individual provinces and not the national total.

The air transportation recalculations do not affect the overall air transportation emissions reported in the NFR table. However, only a portion of those emissions are reflected in this report, whereas all flights segments were previously included in this reported. The change will results in an apparent decrease of 456 tonnes (67%) for 2013, and an apparent decrease of 488 tonnes (69%) for 2017.

3.4 Sources of uncertainty

A key source of uncertainty associated with black carbon inventories is the inconsistencies between definitions and measurements of black carbon (Bond et al. 2013). Scientists use different methods to measure black carbon particle emissions at the source and in the atmosphere, and therefore measured quantities are not strictly comparable.

Although not quantified, uncertainty in the black carbon estimates in this inventory stems primarily from the uncertainty around the BC/PM2.5 fractions. There is large variability in the size of measurement samples used to derive these fractions; the same fractions can by default be applied to several different technologies. An example of the limitation of available BC/PM2.5 fractions can be seen with the application of the diesel BC/PM2.5 fraction for aviation turbo fuel in jet aircrafts, as there is no available fraction specific to aviation turbo fuel. Similarly, a single BC/PM2.5 fraction is applied to all residential wood combustion appliances except wood furnaces (Annex C, Table C–1). The refinement of BC/PM2.5 fractions is dependent on new measurements. Assignment of fraction to sector or equipment type is made using engineering knowledge and judgment based on limited available information (such as stack names), with varying degrees of accuracy.

There is high uncertainty in determining the proportion of combustion PM2.5 emissions from industrial sources. The primary data source for estimating PM2.5 emissions from many industrial sources is the NPRI, in which emissions are reported by facilities by stack or as one aggregate value for the facility as a whole and are not broken down between combustion and non-combustion emissions. For some sectors (such as aluminium, pulp and paper and cement and concrete industries), it is assumed that the PM2.5 emissions are combustion-related when emissions of both CO and NOx are reported from the same stack; this assumption contributes to the overall uncertainty.

3.5 Considerations for future editions of this inventory

Future improvements will focus on expanding current coverage, as well as improving the accuracy of emission estimates, including the following:

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