Measurement uncertainty – implications for the enforcement of emission limits

INTRODUCTION

The second generation EC Directives such as the Waste Incineration Directive (WID), Large Combustion Plant Directive (LCPD), Solvents Directive (SD) and the Pollution Prevention and Control Directive (IPPC) impose not only emission limits on individual pollutants but also specify the measurement uncertainty that has to be achieved by automated monitoring systems and incorporated in the process of regulation. This approach creates a link between the Directives and a variety of auxiliary standards describing the monitoring techniques, calibration methods and measurement quality assurance and management.

Despite the fact that measurement uncertainty requirements are clearly stated in the Directives it is difficult for regulatory authorities across Europe to ensure that they have resolved this issue in a comparable and consistent manner and have effective implementation procedures. One of the problems encountered by the regulatory authorities is that the measurement uncertainty assessment methodologies established for air emissions do not translate well into other media such as water and land where the custom and practice are substantially different. Another problem has been continuing adherence to the methodological principle of reliance on manual standard reference methods (SRMs) that have been left behind by rapidly advancing technology, no longer reflect best available techniques, and may not be best suited to act as a basis for measurement qualitymanagement.

The objective of this paper is to examine the way in which the measurement uncertainty is estimated and to find the best way of using uncertainty information in the regulatory process. The philosophy of compliance assessment is also reviewed in order to establish the best practice allowing for technically sound and legally robust approach where a measure of noncompliance
severity is defined leading to different follow-up actions.