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

Abstract

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.

A Re-Examination of Ambient Air Ozone Monitor Interferences

“…More substantial Hg interference may be encountered near Hg sources 10 or perhaps during wildfire plume events. 29 Li et al 11 report instances of indoor Hg levels up to 523 ng/m 3 . Although indoor sources include broken thermometers, fluorescent lights, or other electrical devices as noted by Li, cultural practices that include wearing Hg ampoules or sprinkling Hg about homes and vehicles also result in elevated microenvironmental levels.…”

“…The 6.8-ppt mixing ratio approaches common ambient air levels, whereas the higher Hg mixing ratio might represent a nearby Hg emission source. 10,11,23 Test A in Table 5 was carried out under dry conditions (RH Ͻ 3%), and test B was carried out with humid air (RH ϳ80%); the response ratios are tabulated as ppb of apparent O 3 per ppt of Hg.…”

“…Several studies have examined individual chemical interferences to UV O 3 monitors. 2,3,[5][6][7][8][9][10][11][12][13] To interfere with the UV method a chemical must absorb light at the 254-nm wavelength used for O 3 detection and be at least partially removed from the sample air by the scrubber. This situation causes a positive bias.…”

“…Concerns have been raised about potential interferences to the UV method caused by aromatic hydrocarbons, their photochemical reaction products, 2,[5][6][7][8][9][10] Hg vapor, 3,11,12 sulfur dioxide, 13 and water vapor. 3,4,14 -16 UV instruments use scrubbers containing MnO 2 , Hopcalite (a mixture of Cu and Mn oxides), or heated silver wool (HSW).…”

Use of a heated graphite scrubber as a means of reducing interferences in UV-absorbance measurements of atmospheric ozone

“…Gaseous mercury is a particularly strong interference because the electronic energy levels of Hg atoms are resonant with the Hg emission line used in most ozone monitors. The relative response of mercury has been estimated at ∼ 1 ppb O 3 /ppt Hg (Spicer et al, 2010;Li et al, 2006). So even a few ppt of mercury vapor can potentially cause substantial biases in ozone measurements.…”