AIR QUALITY INDEX(AQI)
WHAT IS AIR QUALITY INDEX(AQI)?
- AQI measures how safe the air around you is for breathing.
- Organizations that report AQI measure the density of various pollutants in the air (such as PM2.5, PM10, nitrogen dioxide, ozone, etc) at different monitoring stations, in micrograms per cubic metre.
- A particular amount of one pollutant may not be as harmful as the same amount of another pollutant.
- So, each pollutant’s quantity in the air is adjusted to a common scale (say, 0 to 500) that works for all pollutants.
- Finally, the pollutant with the worst sub-index determines the AQI for that time and location.
OFFICIAL AQI SCALING:
- The widely-used National Air Quality Index (NAQI) given by the Central Pollution Control Board is a 24-hour average.
- All the eight pollutants may not be monitored at all the locations.
- Overall AQI is calculated only if data are available for minimum three pollutants out of which one should necessarily be either PM2.5 or PM10.
- Else, data are considered insufficient for calculating AQI.
- Similarly, a minimum of 16 hours’ data is considered necessary for calculating sub-index.
NATIONAL AIR QUALITY INDEX (NAQI):
- 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.
- 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.
REAL-TIME AIR QUALITY MEASURE:
- The AQI given by the Ministry of Earth Sciences’ SAFAR unit is real-time, which is commonly cited.
- SAFAR’s AQI is different from the CPCB’s AQI.
- The latter will be markedly lower if there have been phases of better air in the preceding 24 hours.
DIFFERENCE BETWEEN HAZARDOUS AND SEVERE:
- The CPCB and SAFAR indices are categorized into good, satisfactory, moderate, poor, very poor, and severe, with an additional “severe- plus/emergency” label for 500+ in SAFAR.
- The World Air Quality Index Project uses good, moderate, “unhealthy for sensitive groups”, unhealthy, very unhealthy, and hazardous.
- Moreover, the apocalyptic AQI of 999 seen in past years isn’t possible on the CPCB index since it caps the AQI at 500, but is possible on others.
SYLLABUS: PRELIMS, ENVIRONMENT
