Metrology for Air Pollutant Emissions Emission limits are enforced by measurements using techniques (instruments) operated in accordance with documentary standards published by CEN these conventionally being referred to as Standard Reference Methods (SRMs) and either being passed into or referred to, in member state legislation. There are now European directives regulating emissions from large scale processes, such as power stations, all the way down to domestic boilers burning fuels such as wood pellet. New directive requirements have a two-fold impact in that they are bringing in ELVs for previously unregulated emissions species and also increasingly stringent ELVs for species currently regulated. This is beginning to expose gaps in the capabilities of techniques and SRMs, potentially undermining the ability of national regulators for fulfil their legal responsibilities to enforce such limits. On the large scale there are no SRMs for HF, NH3 and formaldehyde, and there are questions over whether the existing SRMs for HCl and dust will be able to enforce increasingly stringent ELVs. With respect to small-scale biomass, there are no SRMs for semi-volatile organic compounds (SVOCs), organic gaseous carbon (OGC), polyaromatic hydrocarbons (PAHs) or particulate matter (PM). There is no on-line measurement technique to apportion CO2 emissions as renewable or fossil fuel derived. Also, cutting across all industrial processes there are some significant issues with flow uncertainty, as with small ducts there is a lack of any work identifying and quantifying sources (needed for dust measurements) and with large processes work is needed to validate existing uncertainty knowledge and develop novel lower uncertainty techniques. Lastly, as acknowledged by the EC, the current legislation will not meet WHO air quality guidelines, and so work is needed now on the next generation of techniques to enforce ELVs in future legislation.