The cities in the Helsinki metropolitan area have a joint emergency plan in case of a sudden weakening of air quality. When street dust concentrations become high, the Environment Services can submit a request for action irrigate street surfaces with a dilute calcium chloride solution.
The request can cover busy street traffic routes or the entire road network. The streets to be irrigated are listed in a separate map.
The irrigation is carried out using calcium chloride, as it keeps the dust moist for a long time and thus suppresses dust. The solution can also be used in sub-zero temperatures. In recent years, calcium chloride has been used for street suppression every spring.
When street dust concentrations in the city’s main routes rise, HSY sends a message to the Road Traffic Centre, from where the irrigation request is forwarded to the contractors responsible for maintaining the main routes.