Reporting sulphur dioxide emissions based on fuel sulphur content
Updated 20 January 2026
Applies to England
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This guidance provides an approach for calculating the sulphur dioxide (SO2) content of stack gas emitted by medium combustion plants (MCPs).
Calculating the SO2 emission from the fuel sulphur content, assuming complete oxidation of the fuel sulphur, is often used instead of directly measuring SO2 in stack gas. This is only for plants that are not fitted with flue gas desulphurisation abatement.
The medium combustion plant directive (MCPD) requires that you carry out emissions monitoring when firing a fuel (or fuel mix) that is likely to result in the highest level of emissions. You must calculate the SO2 emission from sulphur at the highest representative fuel sulphur content fired during the compliance period.
1. Liquid fuels
The sulphur content of gas oil is regulated under the The Sulphur Content of Liquid Fuels (England and Wales (Amendment) Regulations 2014.
The MCPD does not specify an SO2 emission limit value (ELV) for gas oil. This also applies to other similar low sulphur fuels with a sulphur content less than 0.1% by mass, such as biodiesel and burning oil.
Table 1 provides the approximate liquid fuel sulphur equivalence to ELVs specified in the MCPD. These are for firing liquid fuels (but not gas oil) for combustion plants (at 3% O2) and engines or gas turbines (at 15% O2) that do not have flue gas desulphurisation abatement.
To demonstrate compliance, the sulphur content of the fired fuel must be lower than the applicable threshold values.
Table 1 applies to petroleum fuels, ranging from light to heavy fuel oil with a net calorific value in the range 39.5 to 42.5 MJ/kg.
As an alternative to stack gas measurement, you can report SO2 emissions using the maximum value of the fuel sulphur during the compliance period. Get the fuel sulphur content from the supplier as either a measured value, or as a maximum fuel sulphur specification.
Alternatively, you can use sulphur results of fired fuel samples from an appropriately accredited analytical laboratory.
Table 1: Liquid fuels other than gas oil: fuel sulphur equivalence to ELVs
| Fuel sulphur % by mass | ELV SO2 (mg/m3) at 3% O2 | ELV SO2 (mg/m3) at 15% O2 |
|---|---|---|
| 0.2% | 350 | 120 |
| 0.5% | 850 | 290 |
| 1.0% | 1700 | 570 |
2. Solid fuels
Table 2 provides the approximate solid fuel sulphur equivalence to ELVs specified in the MCPD. These are for firing solid fuels at combustion plants (at 6% O2) that do not have flue gas desulphurisation abatement.
To demonstrate compliance, the sulphur content of the fired fuel must be lower than the relevant threshold values. Table 2 applies to biomass. Table 3 applies to commercially traded hard coal.
There will be some absorption of SO2 by the fuel ash. This will depend on the composition of the ash and the type of dust abatement plant installed. Coal ash typically absorbs up to 5% of the released SO2. Biomass ash can absorb much higher proportions of the released SO2. The fuel sulphur thresholds given in Table 2 and Table 3 are therefore conservative.
In situations where the fuel sulphur is higher than this threshold but there is significant ash absorption, you must measure the stack gas emission to demonstrate compliance.
Table 2: Solid biomass, fuel sulphur equivalence to ELVs
| Fuel sulphur % by mass (as received) | SO2 ELV (mg/m3) at 6% O2 |
|---|---|
| 0.058% | 200 |
| 0.087% | 300 |
Table 3: Hard coal, fuel sulphur equivalence to ELVs
| Fuel sulphur % by mass (as received) | SO2 ELV (mg/m3) at 6% O2 |
|---|---|
| 0.174% | 400 |
| 0.477% | 1100 |
There are no ELV and reporting requirements for plants firing exclusively woody biomass. Dried biomass pellets can be assumed to contain 10% moisture.
The solid fuel sulphur content is based on the ‘as received’ fuel at the applicable moisture content, not the dry or dry, ash-free fuel. To determine the ‘as received’ sulphur content, multiply the dry sulphur content by (1 − % moisture ÷ 100%).
3. Determining the reportable SO2 concentration
You can determine the reportable SO2 concentration in mg/m3 at 273K, 101.3kPa by scaling the SO2 concentrations, equivalent to 0.1% fuel sulphur, by the following factors:
- fuel oil factor at 3% O2 is 169
- fuel oil factor at 15% O2 is 56
- solid biomass factor at 6% O2 is 344
- hard coal factor at 6% O2 is 230
For example:
- boilers firing liquid fuel with a sulphur content of 0.25% will emit an SO2 concentration of 422.5 mg/m3 at 3% O2 [= (0.25%/0.1%) × 169 mg/m3]
- gas turbines firing liquid fuel with a sulphur content of 0.05% will emit an SO2 concentration of 28 mg/m3 at 15% O2 [= (0.05%/0.1%) × 56 mg/m3]
- boilers firing dried biomass with a sulphur content of 0.02% will emit an SO2 concentration of 68.8 mg/m3 at 6% O2 [= (0.02%/0.1%) × 344 mg/m3]
4. Using factors for other fuel types
If you want to report SO2 emissions based on fuel sulphur content of other types of fuels, you must first get approval from the Environment Agency.
Contact MCPReturns@environment-agency.gov.uk for standard rules permits or your local compliance officer for bespoke permits.