Facility reports capture only part of the pollution in any area. The NPI NEPM therefore provides for aggregated emissions data, estimates of emissions from facilities that are not reporting facilities and from other human-caused sources.
Key points
- Also called aggregated emissions data
- Covers non-reporting sources such as vehicles and wood heaters
- Prepared by state and territory governments
- Much older than the annual facility data
- Some states hold more recent regional inventories
Who prepares the estimates
Under clauses 8 and 20 of the NEPM, state and territory governments develop the aggregated emissions data. DCCEEW publishes diffuse emissions manuals for this work.
What sources are included
Typical diffuse sources are motor vehicles, domestic wood heaters, lawn mowers, and small businesses that fall below the reporting thresholds.
How current the data is
DCCEEW states that the diffuse data is much older than the annual industry data, that large parts of Australia have not been modelled, and that there are no current plans to add new diffuse data.
Aggregated transfer data
The NEPM also provides for aggregated transfer data, meaning estimates of substances transferred by non-reporting facilities and other human-caused sources.
Using diffuse data with facility data
Aggregated estimates are needed to understand the total load in an airshed or catchment. When comparing a facility’s emissions with the total for an area, check the year of the diffuse estimate, because it may be many years older than the facility data.
More recent regional inventories
- New South Wales Greater Metropolitan Region inventories for 2005, 2008 and 2013.
- A Victorian inventory for 2016.
- A Perth inventory for 2011-12.
These inventories were prepared by state governments. Where no recent state inventory exists, the NPI diffuse estimates may be the only published figures, which is another reason to check their date before relying on them.
Why it matters
The 2021 review of the NPI NEPM recommended modernising aggregated data along with the substance list, thresholds and estimation manuals. Until that happens, diffuse estimates should be read as indicative rather than current. Anyone comparing a facility’s emissions with a regional total should state which diffuse dataset and year they used.
References & sources
Primary regulatory documents and authoritative references underpinning this answer.