How do AQI readings work? Why do the pollution board and IQAir data differ?

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. Commuters drive amid dense smog in New Delhi 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. 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. 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.