An air quality index (AQI) is a number used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become1. This is not a universal scientific scale. It varies from country to country.

Air Pollution Concentration

Air pollution is usually measured in μg/m3 (micrograms of pollutant per meter cube of air). This is a scientific measure. It is converted to the Air Quality Index of specific countries using scales such as the ones given below.

The US EPA Scale

This is the pollution scale used in the USA2.

PM2.5 AQI scale
Concentration: 0 12 35.5 55.5 150.5 250.5 350.5 500.5
AQI Range:
0..50
50..100
100..150
150..200
200..300
300..400
400..500

 

PM10 AQI scale
Concentration: 0 55 155 255 355 425 505 605
AQI Range:
0..50
50..100
100..150
150..200
200..300
300..400
400..500

The Indian AQI Scale

This is how India declares pollution levels3.

Indian AQI scale
PM2.5 Concentration: 0 30 60 90 120 250
PM10 Concentration: 0 50 100 250 350 430
AQI Range:
0..50
50..100
100..200
200..300
300..400
400..500

 

AQI Associated Health Impacts
Good (0-50) Minimal impact
Satisfactory (51-100) May cause minor breathing discomfort to sensitive people.
Moderately polluted (101–200) May cause breathing discomfort to people with lung disease such as asthma, and discomfort to people with heart disease, children and older adults.
Poor (201-300) May cause breathing discomfort to people on prolonged exposure, and discomfort to people with heart disease.
Very poor (301-400) May cause respiratory illness to the people on prolonged exposure. Effect may be more pronounced in people with lung and heart diseases.
Severe (401-500) May cause respiratory impact even on healthy people, and serious health impacts on people with lung/heart disease. The health impacts may be experienced even during light physical activity.