Air quality index

With the help of the air quality index, the concentrations of different pollutants are divided into five categories, from good to very poor. The air quality index is a simplified way of illustrating real-time (hour by hour) air quality.

The index is based on health impacts, limit values and guidelines for air quality. When air quality is poor, health impacts are possible on sensitive individuals.

Sub-indices are calculated for sulphur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), ozone (O₃), fine particles (PM_2,5) and thoracic particles (PM₁₀). The highest detected value determines the air quality index. The index rating is 100 when anyone of the concentrations meets the guideline or limit value level.

Table: Air quality classes and the connection between health impacts

 Class    Health impacts  Other long-term   impacts
 Very poor    Adverse effects possible on sensitive subpopulation  Clear impacts on vegetation, material impacts
 Poor    Adverse effects possible on sensitive individuals  Clear impacts on vegetation, material impacts
 Fair    Unlikely effects  Clear impacts on vegetation, material impacts
 Satisfactory    Very unlikely effects  Mild environmental impacts
 Good    No health effects  Mild environmental impacts

Table. The concentrations behind the classes of the finnish air quality index since april 2007.

 Air quality
(value)  CO  NO₂  SO₂  O₃  PM₁₀  PM_2.5  TRS
 Good
(<50)  <4  <40  <20  <60  <20  <10  <5
 Satisfactory
(50-75)  8  70  80  100  50  25  10
 Fair
(75-100)  20  150  250  140  100  50  20
 Poor
(100-150)  30  200  350  180  200  75  50
 Very poor
(>150)  >30  >200  >350  >180  >200  >75  >50
Unit per hour, mikrograms per cubic meter (µg/m³), carbon monoxide CO (mg/m³).
For an example: When the number of air quality index rises above 51, the air quality turns from good to satisfactory.