Key takeaway
What This Development Means
England's Environment Agency has revised its M20 guidance for continuous emissions monitoring systems, adding a 2.5 mg/m3 dust trigger for repeat calibration, changing virtual emission-limit values and updating test-gas and failed-test reporting rules. Operators, laboratories and equipment suppliers should apply the revised expectations now where permits require continuous stack-emissions monitoring.
Does Revised M20 Create New Emission Limits?
No. M20 is technical guidance for quality assurance of compliance monitoring. Its virtual values support variability and acceptance tests where no emission limit exists. Installation permits, applicable legislation and other regulatory decisions continue to determine enforceable emission limits.
When Does Low Dust Require A Repeat QAL2?
Seven consecutive daily average indicated concentrations above 2.5 milligrams per cubic metre require QAL2 within six months. If any concentration measured during an annual surveillance test exceeds 2.5 milligrams per cubic metre, the guidance requires repeat QAL2.
Source basis: Environment Agency, Monitoring stack emissions: quality assurance of continuous monitoring, technical guidance note M20
CEMS Quality-Assurance Guidance Changes In England
The Environment Agency has revised its M20 CEMS quality-assurance guidance for permanent continuous emissions monitoring systems used for compliance in England. The update, published on 14 September 2026, changes calibration, test-gas and reporting expectations.
M20 supports EN 14181, which uses quality-assurance levels QAL1, QAL2 and QAL3 plus an annual surveillance test. Equipment suppliers maintain certification and install suitable systems, accredited laboratories perform standard reference method work, and operators retain overall responsibility for compliance, ongoing QAL3 control and records.
New Dust And Calibration Conditions
Where dust emissions are too low for gravimetric calibration, an operator may configure the monitor to output the default value on its QAL1 certificate. The reading is indicative but may be used for compliance assessment, mass-emission reporting and process control.
The revised section 3.7.4 now sets a clear escalation point. If seven consecutive daily average indicated dust concentrations exceed 2.5 milligrams per cubic metre, the operator must complete QAL2 within six months. Any concentration above 2.5 milligrams per cubic metre during an annual surveillance test requires repeat QAL2. Energy-from-waste operators using an indicative monitor must set a precautionary alarm at 100 milligrams per cubic metre against an abnormal-operation emission limit value of 150 milligrams per cubic metre.
For low-level clusters under procedure c, standard reference measurements must verify monitor response. Surrogate calibration gases must come from accredited suppliers and have combined uncertainty, including any gas blender, no greater than 2%. Clean, dry ambient air may now be used for oxygen.
Virtual Limits And Failed-Test Reporting
For measurands without permit emission limits, M20 now specifies virtual daily values and uncertainty allowances for variability testing: ammonia at 10 milligrams per cubic metre and 40%, carbon dioxide at 10% or 1.2 times the maximum paired-test result and 10%, and nitrous oxide at 50 milligrams per cubic metre and 20%. Laboratories may use 20% for carbon monoxide variability and 30% or 2.5 milligrams per cubic metre for dust. These figures are test criteria, not new legal emission limits and are not subtracted from reported results.
Annual surveillance test failures must be reported. A repeat QAL2 based on additional data collected during the failed test may share one report. If corrective maintenance occurs first, the repeat QAL2 requires a separate report cross-referring to the failure report.
Operators should update procedures, laboratory instructions, alarm settings and reporting templates. Analysis, clearly identified as an inference: the 2.5 milligrams per cubic metre trigger converts a previously difficult low-dust judgement into an auditable trend rule, making data review and timely escalation as important as instrument maintenance.
Related Foresight resources cover Environment Agency airborne PFAS monitoring, nitrogen oxides and sulphur dioxide.
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