Air Quality Index

 

 

1.Air Quality Index is a tool for effective communication of air quality status to people in terms, which are easy to understand. It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour.

 

2.  There are six AQI categories, namely Good + Satisfactory, Moderately polluted, Poor, Very  Poor,  and  Severe.  Each  of  these  categories  is  decided  based  on  ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints). AQ sub-index and health breakpoints are evolved for eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short-term (upto 24-hours)
National Ambient Air Quality Standards are prescribed.

 

3.Based on the measured ambient concentrations of a pollutant, sub-index is calculated,
which is a linear function of concentration (e.g. the sub-index for PM2.5 will be 51 at concentration 31 µg/m3, 100 at concentration 60 µg/m3, and 75 at concentration of 45
µg/m3). The worst sub-index determines the overall AQI. AQI categories and health breakpoints for the eight pollutants are as follow: 

 

 

 

 

 

AQI Category(Range)

 

PM10

24 – hr (µg/m3)

PM2.5

24 – hr (µg/m3)

NO2

24 – hr (ppb)

O3

8 – hr (ppb)

CO

8 – hr (ppm)

I low

I high

C low

C high

C low

C high

C low

C high

C low

C high

C low

C high

Good

0

50

0

50

0

30

0

21

0

25

0.0

0.9

Satisfactory

50

100

50

100

30

60

22

43

26

51

1.0

1.7

Moderate

100

200

100

250

60

90

44

96

52

86

1.8

8.7

Poor

200

300

250

350

90

120

97

149

87

106

8.8

14.8

Very Poor

300

400

350

430

120

250

150

213

107

381

14.9

29.7

Severe

400

500

430

700

250

380

214

750

382

450

29.8

40