RoadAir - Road network emission and dispersion model
The effect of road traffic pollution on urban populations is still a major problem in urban areas. Some measures to reduce this effect are:
- Reducing the total amount of traffic, via economic instruments, town planning, legislation or physical restriction.
- Moving traffic away from residential areas, e.g. by constructing ring roads.
- Improving traffic flow/avoiding congestion, by increasing the capacity of the road network.
- Improving vehicle technology, by applying stricter emission regulations and increasing the renewal rate of the vehicle fleet.
Traffic planners are often in need of practical tools for studying the effect of such measures on the environment.
NILU has developed a personal computer-based model RoadAir, for quantitative descriptions of air pollution along road networks. RoadAir calculates total emissions, concentrations along each road segment and the air pollution exposure of the population along each road. Calculations can be carried out for road networks, defined by road and traffic data. The model was primarily developed for conditions in Scandinavia, but can easily be adapted to conditions in other parts of the world.
The pollution concentrations near a road with a given volume of traffic is closely related to the local dispersion conditions. The model calculates maximum concentrations that occur in periods with poor dispersion conditions (eg. during winter or nighttime).
The contribution from other pollution sources is accounted for by adding a city background concentration to each road link. Different background concentrations can be added to different parts of the calculation area.
The geometry of each road link must be described by its length, width, steepness and whether it is characterised as a street canyon or an open area.
The traffic data are given on a daily basis for calculation of total emissions, and on an hourly basis for concentration calculation during rush hours. If no rush hour traffic data are available, the model assigns standard values depending on the road type.
The vehicle fleet must be described by fractions of light and heavy duty vehicles on each road. The model assigns standard distributions of technology types within classes of vehicles. The emission calculations take into account vehicular age distribution, effects of cold starts, and road steepness. Local emission factors might be employed in the model.
The population distribution is described by the position of private homes relative to the road links. An average number of residents per home must be given.
Modelling of the traffic patterns which often represent the input to RoadAir, has to be performed prior to the application of RoadAir.
- Total emissions of NOX, CO2 and CO for the road network. Emissions are also specified for each road link.
- Concentrations of NO2 and CO at a chosen distance from the curb for each road link.
- Tables with number of road links and length of road with concentrations above chosen levels.
- Tables with number of people exposed to various concentration levels of NO2 and CO for each road link, and in total along the road network.
- Calculations of suspended particle (PM10)-concentrations have been included in RoadAir for areas where studded tyres are in use.