Measurement of ambient ozone using newly developed porous glass sensor

An accumulated sensor with an hourly resolution has been developed for ambient ozone monitoring. The sensor operates by employing the reaction of ozone with indigo carmine. This reaction results in colorless reaction products in pores that can be determined by measuring the transmittance of the color change. Transparent porous glass is used as a substrate whose very large surface area is an advantage for gas sensing. Direct, on-site measurements are possible because of the use of the transparent substrate, and no chemical analyses are needed. The sensor is used to analyze exposure to ozone. The detection limit of the sensor is about 3 ppb for a 1 h exposure. The interference from nitrogen dioxide amounts to about 25%. The method is suitable for hourly to daily mean measurements of ambient ozone. Under indoor conditions, the correlation coefficient between the hourly ozone concentration indicated by our sensor and by a UV-photometric monitor for 3 months was 0.84, indicating good agreement.