Standard to certify the purity of zero gas in ambient air measurements

Short Name: Zero Gas, Project Number: 15SIP01
Image showing a meadow in the mountains
Meadow in mountains

A revised standard to ensure traceable calibration of pollution monitoring instruments in support the Air Quality Directive

Environmental policies, as implemented by the 2008 Air Quality Directive and related legislation, have improved air quality over the last decade. However, almost all Europeans remain exposed to polluted air, leading to 400,000 premature deaths a year.

Accurate air pollution measurements rely on ‘zero gases’, used to calibrate instruments or dilute gas samples. However, these gases require very high purity, as even extremely low-level contamination can compromise comparability.

Previous documentary standards had defined requirements for zero gas purity but gave no practical guidance. ISO 19229 included guidance on calculating values and standard uncertainties of impurities but was unsuited to certifying zero gases.

Previous EMRP project MACPoll developed a measurement method and a Certification Protocol to certify zero gas impurity levels, but the protocol had no formal standing.


This project addressed these issues by working with ISO TC 158 to revise ISO 19229. A second edition was published in 2019, incorporating relevant parts of the MACPoll Certification Protocol, including clear guidance on zero gas preparation and gas analyser calibration.

Hands-on training courses on use and data handling were also developed to enhance awareness and skills among users and industrial producers of zero gases. These introduced the revised standard and procedures for assessing impurities.

The work also influenced a number of CEN standards around air pollution, with reference to ISO 19229 included in revisions of EN 14211 (NOx), EN 14212 (SO2), EN 14626 (CO) and EN 14662-1 (Benzene).

Uptake of the Certification Protocol has enabled accurate and unambiguous Zero Gas Calibration Standards, supporting new opportunities for gas and equipment suppliers. Zero gases producers can better deliver accurate and unambiguous Zero Gas Calibration Standards to meet the needs of air monitoring networks.


Increased confidence in the accuracy of monitoring data will enable regulators to apply targeted strategies for air pollution abatement and contribute to cleaner air for European citizens.



Participating EURAMET NMIs and DIs
MIKES-FMI (Finland)
VSL (Netherlands)