We know the values of NOx, CO and soot production for vehicles based on the PIARC reports (for fluent traffic, as well as for traffic jams), the traffic flow from a detailed traffic forecast analysis and the age/fuel type of the cars as brackets from national statistics. This allows us to estimate mean/peak emissions within the tunnel with reasonable accuracy. We know what is the airflow velocity / ventilation capacity for all of the traffic scenarios as well. Now, we have to propose a filtration solution, for which we first need to know, how can we translate our emissions into PM2.5 / PM10.
A very easy assumption for our further modelling, would be that the most of the particulates generated in the tunnel are formed from the soot. I'm not sure if it is possible for larger particulates to form from NOx / O3, as the tunnel is constantly ventilated (either through traffic, or by mechanical ventilation in a traffic stop). I would also assume that mass of soot >>> mass of particulates emitted by breaks, tyres etc., which means we could ignore the latter (especially for traffic stop scenario).
Please share your experience in this (particulate) matter.
There are two sources of particles in road tunnels, engine emissions and tire/break wear. The two types of particles have a size spectrum different from engine emissions consisting of smaller particles. In terms of total mass, you cannot neglect particles from tire wear. If you look at the 2012 PIARC emission report, tire wear is the dominating source of turbidity emission - at least for countries with emission control.
To use the opacity/turbidity emission as given in the PIARC report for an estimate of the PM10 emission, you need a conversion factor, such as the one given in the 1995 PIARC emission report. If this one is applicable to tire wear particulates is another question, as these are significantly larger.
When it comes to tunnel air filtration, there are a few studies available that may assist your work. although it is written in German, the following report may be of interest:
Technical Report Reinigung von Abluft aus Strassentunneln
A problem is that the driving conditions inside a tunnel differs from a normal road
When entering the motor is idling
When in the upward slope there is more power used
Summarising: how to relate emissions with driving conditions that chnage duting passage of cars thru the tunnel
Speak of own experiene of a manuscript rejected on this basis
Ingo, thank you for sharing that document! That is exactly what I needed. It has a great number of practical examples, very useful for us!
Harry, we design different ventilation system performance for different driving conditions, with a complete traffic stop being usually the most difficult to deal with. The inclination is a major factor, but that is already included in PIARC emmission data (just like the car velocity).
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