Guidance

Monitoring stack emissions: low risk MCPs and specified generators

Updated 20 January 2026

Applies to England

How to monitor emissions from low risk medium combustion plants (MCPs) and specified generators (SGs).

This guidance provides a standardised approach to monitoring stack gas emissions from low risk plants regulated under the:

• Medium Combustion Plant Directive (MCPD) 2015/2193/EU Directive on the limitation of certain pollutants into the air from medium combustion plant
• Specified Generator Regulations (SGRs) EPR 2018 Schedule 25B 2 (1) – Specified Generators

This guidance is for operators of:

• MCPs and SGs with standard rules and simple bespoke permits
• other low risk MCPs and SGs
• MCP installations where the Environment Agency has agreed to the use of this standard

1. Monitoring approach

The MCPD states you need reliable, representative and comparable results for:

• sampling and analysing polluting substances
• measuring process parameters
• any alternative monitoring methods you use

Where available and practical to do so, you should use methods that comply with European standards.

Sulphur dioxide (SO₂) emissions can be calculated using sulphur in fuels analysis instead of by directly measuring SO₂ in stack gas. More information is available in Reporting sulphur dioxide emissions based on fuel sulphur content.

The MCPD and SGRs specify that you must standardise your emissions monitoring results to a dry gas, at a standard temperature and pressure (273.15K and 101.3kPa).

You must also report your results corrected to a reference oxygen (O₂) concentration of:

• 3% for liquid or gaseous fuels
• 6% for solid fuels
• 15% for engines and gas turbines

You may use continuous emissions monitoring systems (CEMS) as an alternative to periodic measurements. CEMS must meet the requirements of either of the following Monitoring Certification Schemes (MCERTS):

• MCERTS: performance standards for low risk plant monitors
• MCERTS for stack emissions monitoring equipment at industrial installations

MCERTS is our monitoring certification scheme. You can find more information at Monitoring emissions to air, land and water (MCERTS).

2. Sample locations

If you only need to sample gas concentrations, you can sample at a single point and from a location close to the MCP or SG where the gases are well mixed. For example, you can assume that a downstream location close to the combustion zone is well mixed.

3. Measuring system requirements

Portable monitoring systems, must meet the requirements of either of the following MCERTS schemes:

• handheld emissions monitoring systems
• transportable emissions monitoring systems

The MCERTS certified range of portable monitoring systems must be no more than 6.5 times the emission limit value (ELV).

Where sample probes are exposed to gases at high temperatures (for example, more than 250°C) they must be made of temperature resistant material.

4. Annual quality control

You must carry out a lack of fit (linearity) test annually, or after a major repair to the portable analyser (for example changing an electrochemical sensor). This must be done by a service organisation or other suitable organisation (for example a calibration laboratory or the analyser’s manufacturer).

You must carry out the test following the procedures in EN 15267-4 ‘Performance criteria and test procedures for automated measuring systems for periodic measurements of emissions from stationary sources’. You must assess against the performance criteria for laboratory tests specified by this standard.

You must produce an annual service report for each analyser. You must include a summary of the service work carried out on the analyser and the test results for analyser performance.

If an annual service report shows that a measuring system has failed an annual test, you must review the potentially affected monitoring results. You must send the review to MCPReturns@environment-agency.gov.uk in the case of standard rules permits or your local compliance officer for bespoke permits.

5. Ongoing analyser performance checks

You must check and performance test analysers using the manufacturer’s instructions.

If any checks or tests fail, you must review the potentially affected monitoring results. You must send the review to MCPReturns@environment-agency.gov.uk in the case of standard rules permits or your local compliance officer for bespoke permits.

6. Sample strategy and process operating conditions

The sample strategy may vary depending on the type, age and availability of the MCP or SG.

You can measure performance and emissions at different operating conditions that reflect the MCP’s ability to follow the load. For example, you can measure :

• a burner with 5:1 turndown at 20% and 100% output, along with several intermediate steps
• a simpler, older MCP at low and high fire, taking a medium fire measurement if the MCP can be set for this

You should take each measurement at 30 minute intervals. You must report the maximum value.

Because some MCPs operate intermittently, you can limit the sample periods to a few minutes at a time. This means you will need to adapt the sample strategy to shorter time periods.

You must not include measurement results taken during periods of start-up and shutdown.

7. Emission test procedure

You must follow this procedure.

1. Assemble the sampling system and warm up the analyser according to the manufacturer’s instructions.
2. Before the start of the test, carry out the checks required by the manufacturer’s instructions at the sample location (near the sample port).
3. Insert the sample probe into the sample location. Extract the sample gas at the same rate used during the performance checks. Maintain a constant sample rate during the test.
4. At the end of the test, remove the sample probe from the stack and carry out any checks required by the manufacturer’s instructions, including any zero and span checks.
5. Do not break any seals in the sampling handling system until after you have completed any zero and span checks after the test.

8. Reporting results

The monitoring report must record the following information for each test:

• permit number
• name of the operator and installation
• date of the monitoring visit
• report version number
• site address
• name of the organisation carrying out the monitoring
• date of the report
• unique identification of each emission point
• date and start and finish times of each test
• measurands measured
• ELV (mg/m³)
• concentration measured (mg/m³)
• reference conditions (dry gas, 273.15K, 101.3kPa, O₂ of 3%, 6% or 15%)
• a description of process and operating conditions
• the analyser’s name model number and serial number
• MCERTS certification of the measurement system
• the calibration due date of the analyser

The operator must keep this information for a minimum of 6 years.

9. Quality assurance

The organisation carrying out the monitoring must have procedures that meet the requirements of this guidance.

They must include these procedures in a management system, such as ISO 9001, ‘Quality management systems – Requirements’. The management system must be certified by a United Kingdom Accreditation Service (UKAS) accredited certification body.

We may audit onsite emissions monitoring to check that you are following the procedures described in this guidance. We may also audit the organisations that carry out the annual service and calibration checks of the measurement system.

Organisations that carry out monitoring must provide us with their monitoring procedures, records and work schedules, if requested.

10. Measurement uncertainty

Measurement uncertainty is the range of values in which you will find the true value of an analytical result with a specified level of confidence.

Every measurement has an uncertainty associated with it. This uncertainty can be from errors in sampling and analysis and from imperfect knowledge of the factors affecting the result.

If you are following the monitoring approach in this guidance, you must not exceed an expanded measurement uncertainty of ±20% for nitrogen oxides. This is derived from the measurement uncertainty from MCERTS performance tests and the effect of oxygen correction.

You should correct monitoring results to the required reference conditions and report them to us, without subtracting the measurement uncertainty. After you have reported monitoring results, we will consider the measurement uncertainty when we assess compliance with an emission limit. When assessing compliance for nitrogen oxides, we will use a fixed expanded measurement uncertainty of ±20%.