Srinagar, Nov 11A day after the reliability of air quality data reported by the Central Pollution Control Board (CPCB) came under scrutiny following the sharp deterioration in air quality during the post-Diwali period, the national pollution watchdog issued a detailed clarification. The methodology for calculating and reporting the National Air Quality Index (NAQI) is scientific and reliable.
Kashmir too has seen its air quality readings circulating across online platforms. The readings have created considerable concern and sparked questions about the actual state of pollution here. The J&K CPCB has clarified that readings being shared online are not reliable, and data from monitoring stations show air quality is moderately polluted at some places and good in Srinagar.
The stark difference between readings available on official monitoring platforms and those circulated by private applications has added to public confusion. People have been increasingly relying on online air quality updates.
In its clarification dated November 10, the CPCB has addressed concerns about the capping of AQI at 500. The Board has maintained that these differences arise primarily from variations in measurement techniques, averaging periods and data validation standards.
It should not be construed as under-reporting.
The CPCB has sought to explain that the National Air Quality Index is not intended to showcase every short-lived dip in air quality.
Instead, it is designed to communicate the likely health implications of prevailing air quality, the Board has said.
Under the National Air Quality Index, eight pollutants are monitored in India. These are PM2.5, PM10, carbon monoxide, nitrogen dioxide, sulphur dioxide, ammonia, ozone and lead.
The index is generated using pollutant sub-indices calculated on the basis of the preceding 24-hour average. Carbon monoxide and ozone use an eight-hour average though. The highest sub-index among the pollutants is the overall AQI for that hour.
The CPCB has said this approach is consistent with international practices. It is the same practice followed by the United States Environmental Protection Agency and China.
A major point addressed in the clarification concerns the apparent capping of AQI at 500. The CPCB has explained that 500 is the upper limit of the Indian index. It represents the highest category of health concern, labelled ‘Severe’. An AQI of 500 and higher falls within the same health-impact category.
CPCB has also addressed complaints about missing readings during extreme pollution on and Diwali.
According to the CPCB, particulate matter analysers installed when the NAQI was introduced were calibrated for a measurement range of 0–1,000 micrograms per cubic metre. Readings beyond the calibrated range are automatically treated as outside the instrument’s measurement range.
These are excluded from the computation.
