Seeing a figure like "NOx: 145 mg/Nm³" on a measurement report doesn't tell you anything on its own — which limit it should be judged against depends on the site's capacity band, fuel type, and which Annex-5 group it falls under. Our earlier article covered which regulation applies to which site; this article goes a step further and explains how to interpret the number in front of you.
A limit value depends on three variables
An emission limit value isn't a single fixed number — it sits at the intersection of three variables:
- Facility/capacity band: the regulation's Annex-5 splits facilities into different groups and capacity bands (specific MW ranges, for example). Two facilities in different capacity bands can have different limits for the same pollutant.
- Fuel type: different limits apply to facilities using gas, liquid or solid fuel.
- Reference oxygen basis: as covered in our previous article, limit values are calculated assuming a specific reference oxygen level — 3% for liquid and gaseous fuels, 6% for solid fuels, 15% for gas turbines.
Without correctly matching these three, it's not possible to say whether the number in front of you is compliant or not.
How the reference oxygen correction is applied
An analyser gives a result at the actual O₂ level present at the moment of measurement. That result needs correcting against the regulation's reference O₂ level (3% for gas fuel, for example). The correction is calculated using a factor based on the difference between the measured O₂ level and the reference level — this means that even if two sites running at different excess air ratios show different raw measurement results, their corrected (reference O₂) results become comparable. This correction is calculated automatically by calibrated analyser software; a report should show both the raw and the corrected value.
Example values found in general combustion provisions
Indicative values that can be found in the regulation's general combustion facility provisions include:
| Pollutant | Example value | Note |
|---|---|---|
| Carbon monoxide (CO) | ~200 mg/Nm³ | Under general combustion provisions |
| Sulphur dioxide (SO₂) — gas fuel | ~60 mg/Nm³ | Under general combustion provisions |
| Sulphur dioxide (SO₂) — liquid fuel | ~300 mg/Nm³ | Where low-sulphur fuel isn't used, a mitigation requirement also applies |
This table is not a definitive reference — which Annex-5 group and capacity band it belongs to varies site by site. Its purpose is to give a general sense of the unit (mg/Nm³) and order of magnitude involved, not to hand you the exact figure that applies directly to your site.
What to check when reading a measurement report
- Does the report clearly state which O₂ reference the measurement is corrected against?
- Does the report show both the raw and the corrected (reference O₂) value?
- Was the measurement assessed against your site's correct Annex-5 group and capacity band?
- Has the Emission Measurement Report's validity period expired (two years for facilities under the Environmental Permit and Licence Regulation)?
Who should verify this?
A burner's emission class and the legal limit a site must meet are two different things — the burner manufacturer's declaration doesn't substitute for the site-specific legal limit. Getting the exact limit applicable to your site, and correctly interpreting a report, requires working with an environmental engineer or environmental consultancy firm; the burner service provider carries out the combustion setting and measurement, but interpreting the legal limit is a separate area of expertise.
Frequently Asked Questions
Is the mg/Nm³ value on an emission measurement report enough on its own?
No. Without knowing which reference oxygen level the value has been corrected against, and which capacity band and Annex-5 group the site falls under, "is it compliant?" can't be answered.
Why is the reference oxygen correction applied?
It's applied to fairly compare raw measurement results from facilities running at different excess air ratios; the correction recalculates the result against the reference O₂ level set by the regulation.
Is a burner's NOx class the same as the site's legal limit?
No. The burner's NOx class (under EN 676/267) is equipment performance declared by the manufacturer; the legal limit the site must meet is determined separately and is site-specific.
How long is an emission measurement report valid for?
Two years from the date of the first measurement, for facilities falling under the Environmental Permit and Licence Regulation. ---
About Beray Enerji
Beray Enerji is an Istanbul-based burner service company operating across Türkiye, with primary coverage in the Marmara, Thrace and Aegean regions, providing combustion setting and flue gas measurement. We provide calibrated measurement and reporting, and coordinate with your environmental consultant on interpreting your site's legal limit. For a measurement request, contact us on +90 (000) 000 00 00 or at info@berayenerji.com.
Related services: Burner maintenance · Flue gas analysis · Contact
References
- Regulation on Control of Industrial Air Pollution (Türkiye)
- Environmental Permit and Licence Regulation (Türkiye)
- EN 676 — Automatic forced draught burners for gaseous fuels