New Delhi: Central Pollution Control Board (CPCB) Tuesday said that its analysers, introduced in 2015, were calibrated to measure particulate matter concentrations only up to 1,000 micrograms per cubic metre and could not display readings beyond it on Diwali night for several hours.
The anti-pollution watchdog, which operates several of 60 stations that measure pollution in ambient air, said this a day after TOI reported that its stations had stopped giving data on particulate matter at the peak of Diwali night pollution. Delhi has 60 stations that continuously measure ambient air quality. Of these, 43 are operated by Delhi Pollution Control Committee (DPCC). CPCB compiles all the data from the 60 stations and calculates the 24-hour average AQI. On Diwali night, DPCC gave readings that surpassed 1,000 micrograms per cubic metre. At least at 11 locations, the hourly PM2.5 concentration was above 2,000 micrograms per cubic metre. In four, it was above 3,000 micrograms per cubic metre. CPCB explained that “the particulate matter analysers deployed at the time of introduction… were calibrated for a measurement range of 0-1,000 micrograms per cubic metre. It said that “during extreme episodes, which are occasional like Diwali firecracker bursting, this may appear as a data gap at the particular station, and those hours do not contribute to the 24-hour average of relevant pollutant for concerned station. It added that the AQI’s upper limit of 500 represents the highest level of health concern. Beyond this level, the AQI remains in the ‘severe’ category and extrapolation of the index would not alter the assigned health impact category. ” The capping at 500 is a design feature of the index, CPCB explained.
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“Internal deliberations and consultations with respect to processing of data beyond system design range are under way,” it said. “An AQI of 500 or above indicates almost the same health risk, that is the severe category,” it said. Sunil Dahiya, founder of think tank Envirocatalyst, said CPCB is meant to collect and analyse data that tracks whether the steps, policies and actions taken to cut air pollution are actually working. “Withholding the exact numbers cripples the analysis needed to judge measures taken on the ground, such as restrictions on firecrackers or an outright ban,” he said.
The remaining are operated by CPCB, IMD and IITM. Accordingly consistent with this, the designed system of automated data validation treats hourly readings beyond the calibrated range as outside the range, and such readings are not used in the computation. It may “cause respiratory effects on healthy people and serious health impacts on people with lung diseases. The anti-pollution watchdog added that short-lived spikes of pollutant concentrations in ambient air, such as during the bursting of firecrackers, are episodic and short-lived. CPCB should publish all its data in full, he added. Download the TOI App.