UV-Absorption-Based Measurements of Ozone and Mercury: An Investigation on Their Mutual Interferences

Continuous mercury monitors (CMMs) have the advantage of performing real-time or near real-time measurement, although they are often vulnerable to measurement interferences. For example, CMMs based on atomic absorption spectrometry (AAS) are subject to interferences by components of the sample gas, such as ozone, if they happen to have strong absorption bands or lines overlapping the Hg absorption line. Studies on a selected commercially available CMM showed that 120 ppb of ozone could exert an interference of approximately 63 ng/m on Hg measurement. This interference may consequently affect the risk assessment of human exposure to Hg. On a similar basis, it was found that Hg can also result in significant interferences on an ozone analyzer based on UV absorption. Results showed that Hg at a concentration of 300 ng/m can potentially cause a bias in ozone measurement of approximately 35 ppb, comparable to the average ambient ozone concentration. It should be noted that interferences discussed in this paper are applicable only to UV-absorption-based Hg and ozone analyzers. It is also possible that certain models of such analyzers are not compromised by the reported interferences, and thus, the findings in this work should be considered as analyzer-specific.