O6. Intensity of residual releases to air



O6: Intensity of pollutant releases to air =

Weight of releases [from production processes and, if available, overhead] to air

 / Normalisation factor

Units: tonnes/normalisation factor

Why this indicator is important

Although releases to air are included in the overall residuals intensity indicator (O5), they are of specific interest because they are often implicated in environmental or human health issues. For example, sulphur dioxide (SO2) from industrial processes and fossil fuel combustion contribute to acid rain. Ground level ozone and fine particulate matter contribute to the formation of smog, aggravating respiratory and cardiac conditions.

The indicator represents the intensity of the weight of all releases to air during the reference year. Although it might be difficult or insignificant to track, it is recommended to track the releases to air from overhead as well as production processes.

As noted in the discussion of the residuals intensity indicator (O5), GHGs are not included here. Also, the Toolkit recommends expanding the definition of materials covered beyond those legislated in the national PRTRs. This will ensure that all materials released to air are covered.



This is also an intensity indicator and, as such, may be sensitive to price fluctuations if total factory gate price is used as the normalisation factor. As with the other intensity indicators, it is important to reduce the intensity of residual releases to air but also to reduce the absolute amounts during times of production increases.

A review of the detailed data will help pinpoint which materials, fuels or processes contribute most to this indicator.

Related issues

It is important for the facility to also track releases of its individual air pollutants of concern, e.g., NOx, SOx, persistent organic pollutants (POPs), volatile organic compounds (VOCs), hazardous air pollutants, particulate matter, and/or other pollutants that are priorities for the state, region, locality, and public interest groups. These may be pollutants that are regulated or permitted. The facility should be able to identify which air pollutants to prioritise and confirm this list with its community, regional, or state officials. This level of disaggregation may inform decision making on how to most efficiently or effectively improve environmental performance. For example, the facility may find that it is better to reduce a more toxic but lower volume pollutant than a higher volume pollutant.

As with the general residuals intensity indicator (O5), this does not take into account the relative impacts of the mix of air pollutants released. Methods are available that index individual pollutants based on their impacts but these are either non-standard or too complex for the current Toolkit. The individual pollutants may be of interest locally and could be assessed independently of the Toolkit. For example, if the facility is looking to reduce its SO2 emissions, this value could be considered along with the more aggregate indicators in the Toolkit.


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