World Calibration Centre (WCC-Empa) for Surface Ozone, Carbon Monoxide, Methane and Carbon Dioxide

WCC-Empa was established in 1996, assuming worldwide responsibility for surface ozone, carbon monoxide and methane inter-comparisons at global GAW stations. In 2010, WCC-Empa was also assigned to extend its activities towards carbon dioxide.

The goals of the WCC-Empa are

  • To ensure that measurements are fully traceable to the designated GAW reference
  • To assist stations with regards to instrument and/or measurement problems
  • To improve technical know-how at stations through on-site training


  • Regular system and performance audits at global GAW stations including inter-comparison measurements with traveling standards.
  • Maintaining laboratory and traveling standards for surface ozone, carbon monoxide, methane and carbon dioxide.
  • Ensuring traceability of the WCC-Empa laboratory standards trough regular inter-comparisons with the corresponding GAW Central Calibration Laboratories.
General traceability chain from the primary standards to atmospheric observations (measurements) at sites of a global network. b) Independent verification of traceability by system and performance audit carried out by the World Calibration Centres. Arrows indicate regular comparisons.

WCC-Empa measurements are traceable to

GAW stations audited by WCC-Empa (red triangles)


Benefits of WCC-Empa audits include

  • Improved data quality
  • Increased data availability
  • Improved technical know-how of station operators
  • Increased awareness and acceptance of the GAW programme

WCC-Empa Audits

Further Information
Please direct questions and/or comments about Empa’s GAW activities to  (Head of Department), Martin Steinbacher (QA/SAC Switzerland), or Christoph Zellweger (WCC-Empa).

more about...

Global Atmosphere Watch: Introduction

WCC-Empa (World Calibration Centre for Surface Ozone, Carbon Monoxide, Methane and Carbon Dioxide)

QA/SAC Switzerland (Quality Assurance/Scientific Activity Centre)

CATCOS webpage @ Empa





GAWSIS (GAW Station Information System)

CATCOS Webpage @ MeteoSwiss


Questionnaire: Audit Gases

SOP: Audit Gases

GAW Report No. 229: 18th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases and Related Measurement Techniques (GGMT-2015)

GAW Report No. 213: 17th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases and Related Tracers Measurement Techniques (GGMT-2013)

GAW Report No. 209: Guidelines for Continuous Measurements of Ozone in the Troposphere

GAW Report No. 192: Guidelines for the Measurement of Atmospheric Carbon Monoxide

GAW Report No. 172: Strategy for the Implementation of the Global Atmosphere Watch Programme, 2008-2015

GAW Report No. 166: Joint WMO-GAW / ACCENT Workshop on the Global Tropospheric Carbon Monoxide Observations Systems, Quality Assurance and Applications, EMPA, Dübendorf, Switzerland, 24-26 October 2005.  Editor: Jörg Klausen (WMO TD No. 1335)

GAW Report No. 143: Global Atmosphere Watch Measurements Guide