Using and interpreting data from the National Pollutant Release Inventory

Each year, more than 7 000 facilities across Canada must report their releases and disposals of pollutants to the National Pollutant Release Inventory (NPRI). This information helps the government set environmental priorities and monitor environmental performance. It also allows you to learn about the pollution in your neighbourhood.

The data is published annually and can be accessed through these products:

• NPRI data highlights
• NPRI reports
• NPRI data search tool
• NPRI dashboard
• Maps
• Explore NPRI data

This guide gives a brief overview of the NPRI and provides information about how to use and interpret its data.

Established in 1993, the NPRI currently collects information on the release, disposal and transfer of more than 300 substances.

Releases are direct discharges of pollutants into the environment (air, water, land).

Disposals manage substances and limit their release. Disposals include landfill, land application and underground injection and can be done at the facility (on-site) or elsewhere (off-site).

Transfers represent the sending of substances to other sites for recycling, energy recovery or for treatment before final disposal.

Figure 1 provides more information about the types of releases, disposals and transfers we track.

Reporting Requirements

Facilities must report to the NPRI if they meet the following requirements:

• Employees work more than 20,000 hours per year (approximately 10 full-time employees); or
• The facilities conduct specific activities on-site (such as incineration, wood preservation or wastewater treatment); or 
• They manufacture, process, use or release substances listed in the NPRI beyond their reporting threshold.

The NPRI does not collect information on the following pollution sources:

• natural sources, such as forest fires
• diffuse sources, such as agriculture
• mobile sources, such as vehicles and aircraft
• transboundary pollution, such as from neighbouring countries

The NPRI does not collect information on the following substances:

• substances prohibited or unavailable in Canada 
• substances tracked by other inventories (such as greenhouse gases)
• substances that do not qualify for addition to the NPRI list

To learn more about the reporting requirements and the substance threshold, please refer to the  reporting guide for the NPRI.

Evolution of the NPRI

Since its creation, the NPRI has regularly added and removed substances, lowered reporting thresholds, and removed certain exemptions. These changes allow for the collection of more complete and relevant information on pollutants.

Figure 2 illustrates the impact of these changes to the NPRI on the number of reporting facilities. For example, the addition of seven criteria air contaminants in 2002, and the inclusion of oil and gas facilities in 2003, tripled the number of facilities required to report to the NPRI.

It is essential to consider the changes made to NPRI requirements when analyzing the data, as they can influence annual trends and year-to-year comparisons. Learn more about changes to the program and the substance list over time.

The following requirements will affect 2023 data:

• substances have been added to the NPRI list
• substances have been deleted from the NPRI list
• changes have been made to the reporting threshold and already listed substances

Other data sources

If the NPRI does not cover the substance or source of pollution you are looking for, you can consult other government inventories such as:

• Air Pollutant Emissions Inventory
• Greenhouse Gas Inventory (all sources)
• Greenhouse Gas Reporting Program (facilities)
• Black Carbon Inventory
• Canadian Nuclear Safety Commission

The NPRI contains a wealth of information. This section outlines our data products and the elements to consider when analyzing them.  

You can access NPRI data in a variety of formats:

• NPRI data search tool is a quick and easy way to find information about a particular facility
• NPRI dashboard is an interactive way to visualize the data
• Maps let you explore the data in an intuitive and visual way
• Explore NPRI data are all the files you need for the most advanced analysis

Different ways to analyze the data

You can analyze NPRI data using a number of different variables:

• time (yearly, monthly or quarterly distribution)
• substance (Chemicals Abstract Service (CAS) Registry Number or name)
• industry (NAICS codes)
• geographic location (latitude and longitude, city, province)
• type of release, disposal or transfer
• environmental compartment (air, water, land)

You can also enhance your data analysis by incorporating supporting information, including:

• company and facility information
• estimation methods
• activities that occur at the facility
• sources categories (for example, fugitive emissions, spills and leaks)
• reasons for change in reported quantities
• comments (for example, changes to concentrations, changes to estimation methods)
• information about stacks at facilities
• destinations of either releases to water or transfers
• pollution prevention plans and activities
• breakdown of volatile organic compounds
• concentration of substances released to water or contained in tailings and waste rock
• unit-level information for facilities generating electricity

How to avoid common data analysis mistakes

Use reviewed data

Use the reviewed NPRI data and coordinates (latitude, longitude), as they may differ from those provided by the facilities.

From June to December, the NPRI data search publishes preliminary, unreviewed data, which may contain reporting errors to allow facility operators to revisit their pollution reports. The risk of errors decreases after the quality control performed by the NPRI team in September, with the publication of the reviewed data in December.

Data for previous years can also change as facilities may correct errors or improve their calculation methods. Late submissions are published the following year.

Understand what zero and no data mean

There are several reasons why facilities can report zeros for quantities:

•  the reporting criteria were met, but the substance was not released, disposed and transferred
•  the measured or estimated value of the substance quantity equals to zero
•  the substance is an acid and was neutralized (pH of 6.0 or greater) before exiting the facility

There are two reasons why facilities can report no data for dioxins, furans and hexachlorobenzene:

1.  if the reporting criteria were met, but facilities have no data and cannot find emission factors, they must report “No information available (NI)” in their estimation methods
2.  if the measured quantity is lower than the level of quantification set by Environment and Climate Change Canada, reporting quantities is optional

The dosage limit refers to the lowest concentration of a substance that can be accurately measured using a precise but common analytical and sampling methods.

Pay attention to units of measurement

The quantities can be expressed in different units of measurement, even for similar substances (such as metals) or for the same substance over time. 

The following units are used in the NPRI:

• tonnes
• kilograms (kg)
• grams (g)
• grams of toxic equivalent (g TEQ)

For data expressed in g TEQ, facilities first report in grams (g). Then, a toxic equivalency factor is applied, which is a weighting factor that expresses the toxicity of a dioxin and furan relative to the most toxic congener, to and convert the reported amount to grams of toxic equivalent (g TEQ). Currently, International Toxicity Equivalency Factors (I-TEF) are used.

Avoid double or triple counting

Some substances are subgroups of other substances listed in the NPRI, which can lead to double or triple counting in data analysis. The following section addresses the various cases of double counting in the NPRI data. 

Total reduced sulphur

Total reduced sulphur (TRS) is a gaseous mixture of sulphur compounds. The NPRI only tracks releases to air of TRS.

The NPRI also tracks other individual sulphur compounds that are subsets of total reduced sulphur:

• Carbonyl sulphide (COS)
• Carbon disulphide (CS₂)
• Hydrogen sulphide (H₂S)

Figure 3 shows how double counting can occur when adding TRS to its components.  

Long description

Figure 3 shows two spreadsheets demonstrating correct and incorrect ways to calculate TRS releases to air:

• the sheet on the left shows the correct value, a total of 15,523 tonnes. This is the sum of
  • 5,159 tonnes of carbonyl sulphide
  • 4,458 tonnes of carbon disulphide
  • 2,707 tonnes of hydrogen sulphide
  • 3,199 tonnes of other TRS substances
• the sheet on the right shows an incorrect (double-counted) value, a total of 27,847 tonnes. This is the double-counted sum of
  • 15,523 tonnes of TRS
  • 5,159 tonnes of carbonyl sulphide
  • 4,458 tonnes of carbonyl disulphide
  • 2,707 tonnes of hydrogen sulphide

Depending on the intent of the analysis, it is possible to:

•  use only TRS release value to air
•  use other sulphur compounds for other environmental media
•  focus on a specific sulphur compound

Particulate matter

Particulate matter (PM) consists of microscopic solid and liquid particles, of various origins, that remain suspended in the air for any length of time. The size of those particles largely determines the extent of environmental and health damage caused.

As shown in Figure 4, total particulate matter (TPM) is comprised of any particulate matter with a diameter less than 100 micrometres, including those smaller than 10 and 2.5 micrometres.

Long description

This Euler diagram describes the relationship between the three particulate matter fractions. The total particulate matter or TPM fraction (diameter smaller than 100 micrometres) includes the PM₁₀ fraction (diameter smaller or equal to 10 micrometres). The PM₁₀ fraction includes the PM_2.5 fraction (diameter smaller or equal to 2.5 micrometres).

Release thresholds for particulate matter

Particulate matter	Reporting thresholds (tonnes)
Total particulate matter (TPM)	20
Particulate matter smaller or equal to 10 micrometres (PM10)	0.5
Particulate matter smaller or equal to 2.5 micrometres (PM2.5)	0.3

Depending on the analysis, it is possible to:

•  focus on a specific fraction of particulate matter
• consider only at TPM values
•  consider all three fractions for each facility and use the largest reported value to obtain the most comprehensive method, as is done in NPRI reports

Volatile organic compounds

Volatile organic compounds (VOCs) are precursors to the formation of ground level ozone and ambient particulate matter – the main constituents of smog.

The NPRI lists over 100 VOCs based on various reporting criteria. Facilities may need to report them as:

• total VOCs, under Part 4
• individual VOCs (substances lister in Parts 1 and 2, and speciated compounds under Part 5) 

Long description

This Euler diagram describes the relationship between the four groups of volatile organic compounds reported to the NPRI.

Volatile organic compounds (Part 4) include:

• speciated volatile organic compounds (Part 5)
• Polycyclic aromatic hydrocarbons (Part 2)
• other volatile organic compounds (Part 1)

The fractions for speciated compounds under Part 5 and the other compounds under Part 1A overlap each other. The overlap represents VOCs in both parts 1 and 5, such as aniline, benzene and chlorobenzene.

The sum of the individual compounds may not equal the total of all VOCs under Part 4, because:

• NPRI does not list all existing individual VOCs
• facilities do not need to report individual compounds that are below reporting threshold
• methods used to estimate individual and total compounds vary

Depending on the intent of the analysis, it is possible to:

• only use Part 4 compounds for a general overview, as is done in NPRI reports
• use speciated compounds under parts 1, 2 and 5 for a scientific analysis (for example, air quality modelling)

This section provides essential information to consider before interpreting NPRI data, especially when comparing substances and facilities. It also includes changes that may be observed in the data over time. 

Comparing apples to apples

It is important to compare elements similar to one another and to understand their nuances. The NPRI collects information on various substances, including toxic substances and other substances of concern. The environmental impacts vary between substances and affected environments. The reported quantities can also vary between estimation methods, the facility and jurisdictions.

Comparing substances

Different substances pose different hazards

Compare substances with caution and avoid combining them. Those tracked by the NPRI have distinct physical and chemical properties and they vary in toxicity. A small release of a highly toxic substance like mercury may be a bigger concern than a larger release of a less toxic one. 

Toxic substances

The NPRI tracks certain substances listed on the Toxic Substances List of the Canadian Environmental Protection Act, 1999. To manage risks and environmental impacts, instruments such as regulations, guidelines and codes of practice are used.

Condensable and filterable particulate matter

Although the NPRI only requires information on filterable particulate matter (PM), data on condensable PM can also be found for two reasons:

• some estimation methods may include both types
• the facility used an estimation method for condensable PM instead of the filterable type

Volatile organic compounds

Facilities must report the total mass of volatile organic compounds (VOC) emitted each year. If the emission factors only provide the carbon content of the release, the VOCs must be reported “as-carbon” basis. In this case, facilities must report smaller quantities with an explanatory comment.

Comparing environmental compartments

Environmental compartments include air, water and land. Releases, disposals and transfers affect these environmental compartments in different ways. For example, pollutants released in the air move and behave differently than those released to water or soil. Similarly, substances transferred for disposal or recycling may have a greater impact throughout their journey and at the destination facility than at the originating facility.

As such, you should analyze releases separately from disposals and transfers. Physical and chemical properties also influence compartments differently.

On-site releases

Facilities must separately report releases to air, water and land. However, releases of Part 1A substances below one tonne can be reported as “releases to unspecified media”.

Releases to land and on-site disposals

Releases to land and on-site disposals are different categories. On-site disposals benefit from pollution mitigation measures, unlike releases to land.

Examples of releases to land include:

• spills of solvents on factory floors
• use of a de-icing agent containing ethylene glycol on aircrafts
• accumulation of metal casings at shooting ranges

Tailings and waste rock

Tailings and waste rock are by-products of mining activities. NPRI started tracking the disposal of substances in tailings and waste rock for the 2006 reporting year.

Understand tailings and waste rock

• facilities must report the concentration of substances listed in the NPRI present in the in tailings and waste rock that they dispose of
• facilities may report negative values if they reuse materials from the tailing and waste rock
• differences in geology and in mine types can explain variations in concentration. For example, one extracted ore may contain more arsenic than another.

The NPRI does not collect disposal data on substances contained in inert materials, as they are not released in the environment. They include:

• overburden (unconsolidated materials overlying the ore deposit or bitumen, including, but not limited to, soil, glacial deposits, sand and sediment)
• inert components in tailings
• inert waste rock
• products

Find more information on these exclusions in the guidance for reporting tailings and waste rock. Learn more on how government and industry manage environmental concerns from tailings and waste rock.

Comparing estimation methods

Facilities can use any of the methods below to calculate substance quantities:

• continuous emission monitoring systems or CEMS (M1) record emissions over an extended and uninterrupted period
• predictive emission monitoring (M2) correlates substance emission rates with process parameters
• source testing (M3) involves calculating concentrations with samples collected
• mass balance (C) calculates releases based on the accounting of all input and output materials in a process
• site-specific emission factors (E1) relate activities with releases (these are developed by individual facilities)
• published emission factors (E2) relate activities with releases (these are developed by government entities or industry associations)
• engineering estimates (O) use engineering principles, chemical and physical processes and laws, as well as the design features of the source
• Two new bases of estimate have been added that facilities can use; remote quantification and speciation profile

The degree of accuracy varies depending on the method used and depend on several factors:

• the validity of the method or information used
• the consideration of all operating conditions in the installation estimates
• the quality ranking of the data on emission factors

In general, continuous emission monitoring systems that are properly calibrated are the most accurate, while engineering estimates based solely on judgement are the least accurate.  

It is important to note that calculation methods can differ when you are comparing:

• reports from different years
• facilities of the same industry type
• substances within the same report
• categories of releases, disposals and transfers within the same report

Comparing facilities

The processes or raw materials used to complete the same activity can vary between facilities.

For example, power plants use different fuels and sources of energy to generate electricity. Different processes release different pollutants to the environment. As such, coal-powered generating plants release mostly sulphur dioxide, while diesel-powered plants release mostly nitrogen oxides.

Comparing with other pollutant registers

Other countries have inventories similar to the NPRI. NPRI and data may not be directly comparable between them because reporting requirements (thresholds, exclusions and substance lists) differ. For example, the NPRI covers more sectors than the United States Toxics Release Inventory.

To explore the pollutant inventories of Canada, Mexico and the United States, visit Taking Stock. The Commission for Environmental Cooperation (CEC) hosts this platform, which continues to work on improving their comparability.

To explore other countries’ pollutant inventories, visit the United Nations Economic Commission for Europe (UNECE) website.

Understanding changes

Drivers of change in pollutant trends can be internal (at the facility) or external (regulations and other requirements). We collect information on concentrations and estimation methods to help understand those changes.

Events or changes at facilities

Events or changes at facilities can alter facility data values. Some examples of changes that may affect reported quantities include:

• changes in production levels
• upgrades to operating practices
• plant expansions
• change of ownership
• temporary or permanent closures
• pollution prevention measures
• accidental releases

Regulations and other requirements

Refer to the section Evolution of the NPRI to understand how NPRI requirements have changed over time. In addition, other federal, provincial and municipal governments may also have an effect when they:

• prescribe the methodology used to estimate pollutant releases
• create pollution mitigation tools to reduce emissions
• identify potential new facilities that could be subject to NPRI requirements

Concentrations and method detection limit

The concentration describes the proportion of a substance in either a volume of effluent or a mass of materials. This helps to inform whether large quantities of pollutants come from high concentrations of pollutants or large volumes of effluents or large masses of materials (for example, mineral ore).

You can find concentrations data for the following categories:

• direct discharges to water
• tailings
• waste rock

If measured concentrations of a substance are below the method detection limit (MDL), its smallest detectable concentration, the substance may still be present despite being undetected. In this case, facilities estimate quantities using a concentration of one-half of the MDL.

Evaluating risks

NPRI data is not enough to assess the risks and impacts posed by pollution to the environment and human health. You can combine it with information from other sources and consider factors such as:

• inherent toxicity
• physical and chemical properties (such as, persistence, bioaccumulation)
• the medium (air, land or water) affected by the substance released
• transport and transformation (movement, breakdown) pathways
• amount, timing, nature and level of exposure

The Canadian government assesses broader health and environmental risks through initiatives like the Chemicals Management Plan.

We use the following assumptions and considerations to guide our analyses and public reports.

Use of reviewed data

We use reviewed data for public reports and indicates at which date we obtained the data from the reporting system. Reviewed latitude and longitude coordinates are used for the maps.

Significant figures and rounding

Values, as reported by the facilities, are published on the Open Data Portal and are not rounded.

The NPRI data search tool and data highlights display values using the following rules:

• over 10: no decimal
• between 1 and 10: one decimal
• less than 1: three decimals

Keep in mind that totals in texts, charts and tables may not add up due to rounding.

Negative values

In this guide, we discussed how facilities report the removal of tailings and waste rock as negative values. For our analyses and reports, we use the net value for disposals.

Number of facilities

The total number of reporting facilities in data highlights, sector overviews and other information products excludes (unless stated otherwise):

• facilities only reporting their closure
• facilities that reported they did not meet the NPRI requirements

Substance considerations

Analyses on criteria air contaminants (CACs) include the following 5 air pollutants:

• particulate matter
• carbon monoxide
• nitrogen oxides
• sulphur dioxide
• volatile organic compounds

While ammonia is a CAC, the NPRI excludes it from its CAC analyses. Its substance listing is different from the other air pollutants mentioned above and therefore, the data elements collected are different.

In this guide, we discussed various strategies on how to avoid double counting using the NPRI. These are the following methods we use in our analyses and public reports:

• total reduced sulphur we use total reduced sulphur for releases to air, and use carbonyl sulphur, carbon disulphide and hydrogen sulphide for other categories of releases, disposals and transfers
• particulate matter we use the largest reported value between total particulate matter, PM₁₀ and PM_2.5 for each facility. Direct air releases of particulate matter include road dust emissions
• volatile organic compounds we use Part 4 VOCs for a general overview
• dioxins and furans we use total dioxins and furans for a general overview

Industry classification

The NPRI uses the most recent NAICS codes available to define industry sectors. The classification may vary from one report to another.

Contact the NPRI if you think there are data errors, you need help for your projects or you have any other questions. We strive to improve the quality of our data and ask facilities to verify or update reports when potential errors are detected. These errors can include the following:

• incorrect reporting units (for example, reporting in kilograms instead of tonnes)
• decimal errors
• omitting a substance or the source of a release
• incorrect reference data or assumptions for calculations (for example, reporting quantities manufactured, processed or used instead of quantities released)
• inaccurate geographical coordinates
• inaccurate industry codes

National Pollutant Release Inventory
Environment and Climate Change Canada
351 St-Joseph Boulevard
Gatineau, Québec K1A 0H3

Telephone: 1-877-877-8375
E-mail: inrp-npri@ec.gc.ca