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How do AQI readings work? Why do the pollution board and IQAir data differ?
Delhi pollution: AQI is determined by pollutant with the highest concentration at the time of measurement, assigning that AQI value as overall rating.
As winter sets in, Delhi's air quality has continued to deteriorate, remaining a “very poor” level with 334 overall AQI on Wednesday, according to the Central Pollution Control Board (CPCB).
While the CPCB has recorded the air quality index at 334, another platform, IQAir, a Swiss air quality technology company, showed that Delhi's AQI is around 1190. In fact, it has recorded an AQI of 1696, which is beyond severe, in the Vasant Vihar region of the national capital.
Also Read: Multiple flights affected in Delhi, Punjab amid thick smog due to worsening AQI
AQI, or Air Quality Index, is a numerical scale that measures certain pollutants and their concentration to communicate the quality of air in a specific area. It also provides information on how these numbers can affect human health and the environment.
Also Read: Chandigarh turns into gas chamber; at 343, AQI 2nd worst in country
The AQI scale ranges from 0 to 500, where 0-50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", 401 and 450 "severe" and above 450 "hazardous".
However, even between indices, the way AQI is measured can differ for several reasons.
Monitoring stations
One of the reasons why the data collected by different platforms is varied is due to access to air quality monitoring stations.
Since IQAir is an aggregator, it uses information from government-run sensors, which are also used by the CPCB. It also uses privately operated sensors, which may provide more localised readings.
Real-time data
Platforms such as IQAir update the AQI of a city and its different regions much faster with real-time data, while the CPCB gives one reading which applies to the region for a day. Due to this, the AQI in IQAir will always seem to be fluctuating as it is reacting to changes over an hourly basis.
Different calculations of pollutants
Typically, AQI is calculated based on certain pollutants, such as PM2.5 (particulate matter less than 2.5 microns), PM10 (particulate matter less than 10 microns), ozone, nitrogen dioxide, sulfur dioxide, carbon dioxide, and a few others.
The CPC usually tracks a set of pollutants as mandated by national regulations - which are mentioned above. However, IQAir measures a broader range of pollutants, which may include certain other organic compounds that influence the AQI reading.
