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Uncertainty, Stability and Traceability in Global Monitoring of Atmospheric Composition and the Role of WMO/GAW Central Calibration Facilities – Reality and Plans 

H.G.J. Smit1 and WMO-GAW/ET-ACMQ Team2

1Institute for Energy and Climate Research, Troposphere IEK-8, Research Center Juelich, Juelich, Germany; +49 241 534880, E-mail: h.smit@fz-juelich.de
2World Meteorological Organization, Global Atmosphere Watch, Geneva, Switzerland

The Global Atmosphere Watch (GAW) Program of the World Meteorological Organization (WMO) maintains a global network of long-term observing stations in recognition of the need for improved scientific understanding of the increasing influence of human activities on atmospheric composition and subsequent environmental impacts. Most essential thereby is to rely on most accurate scientific observations of the state of the environment. A set of GAW-Central Facilities supports the quality assurance infrastructure to maintain the long-term stability and traceability of those observations. It has been recognized that stringent requirements for the uncertainty, stability, and traceability of the measurement standards is of crucial importance and therefore remain a key objective for GAW in order to meet the data quality objectives to detect and document changes in atmospheric composition and to understand the underlying processes.

The new GAW Expert Team on Atmospheric Composition Measurement Quality (ET-ACMQ) has started  to evaluate the existing QA-procedures and to facilitate and guide the standardization of the QA-methodologies. We will present an overview of the QA efforts in the GAW observation network and the role of the central calibration facilities. Hereby the focus will be on the accuracy of the observations made in terms of uncertainty, stability and traceability and their reporting for the present state as well future plans for more standardization and harmonization. This will be demonstrated and discussed along a few long term records of GAW observations (e.g. greenhouse gases and ozone) showing that to accurately interpret small long term changes this requires measurement standards with well-characterized uncertainties and well-monitored with maintained stabilities that are reported in a well transparent and traceable way and finally archived as metadata in the data archives.

Figure 1

Figure 1. Traceability within GAW-Quality Assurance System.