Today, more and more tunnel ventilation systems are based on NO2 (or NO) and
visibility measurements. Due to the significant decrease of CO emissions in
countries with EU emission standards, which were adopted by Australia in 2004,
CO is no longer a key factor for tunnel air quality monitoring and is often only
measured for plausibility reasons (eg according to the German guideline
RABT2006). Nitrogen dioxide, which is a good indicator for the overall air
pollution along roads, is now taking over the leading role not only for
ventilation control but also for air quality monitoring and in future probably
for checking the function of air filtration plants in tunnels.
Due to the lack of equipment for reliable and long-term NO2 measurements in
road tunnels in the past, there are only very few standards giving limit values
for NO2 in road tunnels. Furthermore there are not many records of NO2 readings
over longer periods in different types of tunnels.
SICK MAIHAK, a major supplier of measurement devices for controlling tunnel
ventilation, has introduced the first monitor in 2006, specifically designed for
measuring NO2, NO and visibility simultaneously in road tunnels. There are now
experiences and results from the first tunnels equipped with this kind of
This paper will present and discuss the results and experiences from these
tunnels and explain the different levels of NO2 in different tunnel types.
Furthermore, the status of air quality standards for road tunnels regarding NO2
limit values and the current status of discussion in various countries about NO2
limits will be presented.