Concentration scales

The concentration scales for NO2, SO2 and PM10 are based on the new European guidelines concerning the assessment and management of ambient air quality.
Based on the number of allowed exceedances of the new European limit values, an index value of 6, 7 or 8 is assigned to that limit value. The other scale divisions were defined by evaluating the range of concentrations measured in the telemetric networks of the three Belgian Regions.

The concentration scales for O3 are based on the threshold of 180 µg/m³ (European threshold for informing the public) and  360 µg/m³ (alarm threshold) as 1 hour averages.

For CO, the highest percentiles measured in the past correspond to color index 8, 9. Color index 1 corresponds with percentile 30 . There are not enough historic measurements to define a color index for PM2.5.

The table below shows the correlation between the measured concentrations (µg/m³), the concentration scale (between 1 and 10) and the rating for O3, NO2, CO, SO2 en PM10.

Pollutant average unit

scale

O3

1 hour

 µg/m3

0 - 30

31 - 50

51 - 70

71 - 90

91 - 110

111 - 145

146 - 180

181 - 250

251 - 360

> 360

NO2

1 hour

 µg/m3

0 - 25

26 - 45

46 - 60

61 - 80

81 - 110

111 - 150

151 - 200

201 - 270

271 - 400

> 400

CO

1/2 hour

 mg/m3

0 - 1,4

1,5 - 2,1

2,2 - 2,8

2,9 - 3,6

3,7 - 4,5

4,6 - 5,2

5,3 - 6,6

6,7 - 8,4

8,5 - 13,7

> 13,7

SO2

running 24-hour

 µg/m3

0 - 15

16 - 30

31 - 45

46 - 60

61 - 80

81 - 100

101 - 125

126 - 165

166 - 250

> 250

PM10

running 24-hour

 µg/m3

0 - 10

11 - 20

21 - 30

31 - 40

41 - 50

51 - 70

71 - 100

101 - 150

151 - 200

> 200
C6H6

running 24-hour

 µg/m3

0 - 0,50

0,51 - 1,00

1,01 - 1,25

1,26 - 1,50

1,51 - 2,75

2,76 - 3,50

3,51 - 5,00

5,01 - 7,50

7,51 - 10,00

> 10,00
 

color

1

2

3

4

5

6

7

8

9

10

rating

exellent

very good

good

fairly good

moderate

poor

very poor

bad

very bad

horrible