In the City Strategy, the goal is to lower the emissions of the transport system further and also reduce the emissions harmful to health significantly. The air quality in Helsinki has improved other the last few decades, and it is fairly good at an international level. However, the health-based annual limit of nitrogen dioxide, specified in the EU’s Air Quality Directive, is still exceeded or is in danger of being exceeded in places in the city centre’s street canyons. The reason for this is the exhaust emissions from traffic, in particular diesel vehicles. Air quality is also worsened by respirable particles, i.e. dust, especially in spring and in the vicinity of large construction sites. There is still a risk that the limit value for street dust will be exceeded. In dense single-family dwelling areas, the air quality is decreased by the small-scale burning of wood in fireplaces and sauna stoves. In the Helsinki metropolitan area, small particle emissions from fireplaces are even greater than those from traffic. Furthermore, the black carbon in wood smoke warms the climate.
The City’s air protection plan intended to reduce nitrogen dioxide emissions from traffic so that the emissions will fall below the annual limit as soon as possible. In addition to decreasing exhaust gas emissions, the plan focuses on street dust and the small-scale burning of wood. The plan contains 48 measures to be implemented in 2017–2024.
On average, air quality was better in 2019 than in the previous year, and at several measurement locations, the concentrations of contaminants were lower. The concentrations of nitrogen dioxide have decreased especially in recent years, and the annual limit’s exceedance area is estimated to have decreased. In the previous year, no values exceeding the threshold values were measured at HSY’s measurement stations or passive collection stations, but according to an expert estimate, the threshold value is still in danger of being exceeded in a total of 5.5 km of street sections in the inner city area. The concentrations have decreased due to the car stock and HSL’s bus fleet becoming lower-emission. The weather conditions were also good for air quality last year.
Nitrogen dioxide (NO₂) concentrations in ambient air
Annual average nitrogen dioxide (NO₂) concentrations measured by HSY’s monitoring stations and passive samplers, μg/m³
In 2019, the concentrations of respirable particles (PM10) were clearly below the limit values. Due to effective dust prevention, the limit values have not been exceeded since 2006. However, street dust continues to worsen the general air quality and cause significant health hazards in the spring, and the risk of exceeding the limit exists in particular in street canyons with heavy traffic. Continuous efforts towards preventing street dust and developing reduction methods are highly important.
Particulate matter (PM₁₀) concentrations in ambient air
The number of days when the limit value level (50 μg/m³) for particulate matter (PM₁₀) was exceeded in the air quality measurement stations in Helsinki. The limit value is exceeded if the number of days with PM₁₀ levels above 50 μg/m³ is more than 35/year.
The impact of large construction sites on local particle concentrations has been measured in recent years. In 2019, measurements were carried out in Jätkäsaari. Efforts are made to prevent dust emissions in co-operation with contractors, and new methods are being developed in the HOPE project coordinated by Helsinki, among others. The aim is to produce more diverse data on air quality, as well as actions for improving air quality. Pollutant concentrations have been measured by means such as sensors carried by residents in different types of environments. A mobile application to encourage residents to make choices that improve air quality has also been under development in the project.
Efforts are being made to find ways to decrease emissions from the small-scale burning of wood by means such as research projects in which the City is involved. Additionally, residents have been extensively provided with information on ways to influence how cleanly wood burns. The burning method and the dryness of the wood have a major effect on the formation of emissions.
Eyes on the future
Helsinki’s air quality has improved due to the movement restrictions imposed in March 2020 and increased remote work due to the coronavirus. In particular, nitrogen dioxide concentrations have decreased considerably. It remains to be seen whether traffic will return to its growth trajectory after the state of emergency ends or whether remote work will increase enough to affect traffic volumes, for example. Street dust remains a challenge, so influencing winter tyre choices and dust prevention are highly important actions. The emissions from burning wood will continue to decrease air quality in single-family dwelling areas since the use of bioenergy will increase, the residential areas will have new buildings and the fireplace stock is slow to renew.