There are many national and European-wide regulations set for the air that we breathe which aim to ensure a clean and healthy living environment. The most binding regulations concern the limit values of different air pollutants. The limit values define the maximum allowed impurity concentrations in the air for the protection of human health. If the limit value is exceeded, the municipality must prepare and implement air protection plans in order to go below the limit values.
The national guidelines specify the targets set for air quality, and they are mainly intended as instructions for the urban planners and authorities. The World Health Organization WHO has also issued health-based guidelines for the concentrations of other air pollutants. The guidelines issued by WHO are recommendations and based on harmful effects on human health that air pollutants have been proven to cause. The aim of the guidelines is to affect the development of air quality by setting targets in the short and long term.
Other regulations concerning the air are threshold values and target values. The threshold values define the level when a notification or warning about the elevated air pollutant concentrations must be issued. The threshold for issuing a warning is a concentration level in excess of which even a short-term exposure to air pollutants is a risk to health. A threshold for issuing a warning is set for ozone, nitrogen dioxide and sulphur dioxide. However, such high concentration levels do not occur in Finland and in the Helsinki Metropolitan Area. Target values refer to concentrations or load below which the value must fall, where possible, over a given period or after a longer period. The target values are slightly less binding than the limit values.
Table 1. Air quality limit values (The Government Decree on Air Quality 79/2017).
| Compound | Time | Limit value µg/m3 | Permitted exceedances |
| Thoracic particles PM10 | Calendar year | 40 | - |
| 24 hours | 50 | 35 days/calendar year | |
| Fine particles PM2,5 | Calendar year | 25 | - |
| Nitrogen dioxide NO2 | Calendar year | 40 | - |
| hour | 200 | 18 h/calendar year | |
| Sulphur dioxide SO2 | 24 hours | 125 | 3 days/calendar year |
| hour | 350 | 24 h/calendar year | |
| Carbon monoxide CO | 8 hours | 10 000 | - |
| Bentzene C6H6 | Calendar year | 5 | - |
| Lead Pb | Calendar year | 0,5 | - |
Table 1.1. Air quality critical values for protection of natural ecosystems and vegetations.
| Compound | Time | Value µg/m3 |
| Sulphur dioxide SO2 | Calendar year ja winter season (1.10. - 31.3.) | 20 |
| Nitrogen oxides (NO, NO2) | Calendar year | 30 |
Table 2. Air quality national guideline values (The Government decision on air quality 480/1996).
| Compound | Time | Guideline value µg/m3 | Statistical definition |
| Thoracic particles PM10 | 24 hours | 70 | second highest daily mean monthly |
| Total suspended particulate TSP | Calendar year | 50 | annual mean |
| 24 hours | 120 | 98. percentile yearly | |
| Nitrogen dioxide NO2 | 24 hours | 70 | second highest daily mean monthly |
| hour | 150 | 99. percentile monthly | |
| Sulphur dioxide SO2 | 24 hours | 80 | second highest daily mean monthly |
| hour | 250 | 99. percentile monthly | |
| Carbon monoxide CO | 8 hours | 8 000 | running average |
| hour | 20 000 | hourly mean | |
| Total reduced sulfur TRS | 24 hours | 10 | second highest daily mean monthly |
Table 3. Air quality threshold values (VN asetus 79/2017)
| Compound | Time | Information threshold µg/m3 | Alert threshold µg/m3 |
| Ozone O3 | hour | 180 | 240 |
| Sulphur dioxide SO2 | 3 consecutive hours | - | 500 |
| Nitrogen dioxide NO2 | 3 consecutive hours | - | 400 |
Table 4. Target values for arsenic, cadmium, nickel, and benzo(a)pyrene (The Government Decree on Air Quality 79/2017)
| Compound | Time | Target value ng/m3 |
| Arsenic | Calendar year | 6 |
| Cadmium | Calendar year | 5 |
| Nickel | Calendar year | 20 |
| Benzo(a)pyrene | Calendar year | 1 |
Table 5. Target values for ozone (The Government Decree on Air Quality 79/2017).
| Basis | Time | Target value for year 2010 | Long-term objectives |
| Protection of health | 8 hours running average | 120 µg/m3, can be exceeded 25 times per calendar year in three years average | 120 µg/m3, no exceedances |
| Protection of vegetation n | summer* | 18000 µg/m3 h, 5 years average | 6000 µg/m3, no exceedances |
* AQT40 is calculated in time period of 1.5.-31.7. of the hourly values of the time between 9:00 and 21:00 Finnish standard time, which is 10:00 and 22:00 Finnish summer time.
Table 6. WHOs' air quality guidelines for thoracic particles, fine particles and nitrogen dioxide (WHO 2021).
| Compound | Time | Guideline value µg/m³ | Statistical definition |
| Thoracic particles PM10 | 24 hours | 45 | 3 exceedances permitted per year |
| Calendar year | 15 | ||
| Fine particles PM2,5 | 24 hours | 15 | 3 exceedances permitted per year |
| Calendar year | 5 | ||
| Nitrogen dioxide NO2 | 24 hours | 25 | 3 exceedances permitted per year |
| Calendar year | 10 | ||
| Ozone O3 | summer period (march-august) | 60 | verrataan vuorokauden korkeimpien 8 h keskiarvojen keskiarvoa 6kk ajalta. |
| 8 hours running average | 100 | 3 exceedances permitted per year | |
| Carbon monoxide CO | 24 hours | 4000 | 3 exceedances permitted per year |
| hour | 30 000 | ||
| Lead Pb | Calendar year | 0,5 | |
| Cadmium Cd | Calendar year | 0,005 |