A Study Of Reference Methods For Ozone Concentration Measurements

Atmospheric ozone levels are of world-wide concern at ground level where increases in concentration have detrimental effects on public health and the environment, and international effort is focused on monitoring and reducing surface ozone concentra-tions. Global, regional, national and local networks for surface ozone are in operation, and it is important to ensure that measurements and data from these networks are comparable. The comparability of measurements can be assured through their tra-ceability to reference methods and standards with long term stability such as those based on the SI system.A study with three reference methods for ozone concentration measurements is made, which include ultraviolet photometry based on absorption of O3at the253.7nm Hg line, gas phase titration (GPT) of O3with excess NO primary standard, and indigo disulphonate spectrophotometry (IDS).Comparison experiments were made among these independent methods to indicate relationship of consistency or discrepancy. When using GPT to determine the O3mole fraction, it is about2.39%higher than measuring the some concentration by ultra-violet photometry, and the IDS results also show2.46%difference lower than using UV method.The uncertainties associated with the values measured by these three reference me-thods were evaluated, and when considered that the comparison results indicated a good degrees of equivalence.