Sensitive measurement of ozone using amperometric gas sensors

We have investigated the ability of miniature amperometric gas sensors (AGS) to detect ozone in air at concentrations as low as 5 ppb. Baseline drift of the sensor, which occurs on a time scale of hours, can be compensated by periodic correction using sample air scrubbed free of oxidants. Interfering gases expected are nitrogen dioxide and nitrous acid. The latter can be removed with a sodium carbonate-glycerol filter, but a chemical filter that can remove nitrogen dioxide in the presence of ozone is not known. However, filters containing indigo can be used to remove ozone from an air stream without affecting the NO2. Selective and sensitive measurement of ozone was achieved by using two matched sensors connected in series, with an indigo filter between. The first sensor measured ozone plus nitrogen dioxide, whereas the second sensor was exposed only to NO2. The ozone signal is the difference in the two signals.