Experts flag CPCB’s exclusion of peak pollution data from AQI calculations

The Central Pollution Control Board (CPCB) should stop capping particulate matter readings at 1,000 micrograms per cubic metre and make the actual peak values available in the public domain, experts have told The Hindu.The CPCB, in an official statement on Tuesday, said the difference between its AQI readings and those calculated by private entities was due to variations in the measurement of pollutant concentrations and calculation methodologies, and not “under-reporting”.However, experts said excluding peak readings above 1,000 micrograms per cubic metre artificially lowers the calculated AQI, making air quality appear better than it actually is.Responding to reports of missing pollution data on Deepavali night, the CPCB said it measured particulate matter (PM) levels only up to 1,000 micrograms per cubic metre for AQI calculations. Readings exceeding this limit were therefore excluded, resulting in gaps in the data.The CPCB currently records PM readings above 1,000 micrograms per cubic metre as blanks. Experts, however, said that until the methodology is revised to capture actual peak values, such readings should at least be recorded as 1,000 micrograms per cubic metre rather than left blank, to provide a more accurate picture of pollution levels.Peak values are importantManoj Kumar, an analyst at the Centre for Research on Energy and Clean Air (CREA), a Finland-based non-profit research organisation, said missing peak readings of particulate matter (PM2.5 and PM10) artificially lower the AQI, making air quality appear better than it actually is.Dr. D. Saha, former head of the CPCB’s air quality laboratory, said making peak values available in the public domain was essential, as the data was used by policymakers and health experts.“For instance, for people conducting health impact studies, actual peak pollution values will provide better data for their research,” he said.“If there are gaps in government data on air pollution, people may get the wrong impression that the government is fudging the data. We should not let that happen,” he added.Sunil Dahiya, founder and lead analyst at Envirocatalysts, a think tank working on energy and the environment, said authentic and accurate data was essential to tackling air pollution.“Now there are gaps in the data and if the Supreme Court tomorrow asks the CPCB ‘what was the effect of the firecracker restrictions’, they will not be able to answer it properly with the current data and AQI on Diwali,” he said.Deepavali pollution levels 49% higherAccording to a CREA analysis, Delhi’s pollution levels on Deepavali would have been 49% higher if the CPCB had recorded the missing peak-hour readings at 1,000 micrograms per cubic metre instead of leaving them blank.The actual pollution levels could have been even higher, as PM concentrations during the missing hours exceeded 1,000 micrograms per cubic metre, according to data recorded by the Delhi Pollution Control Committee (DPCC), which functions under the Delhi government.“An analysis of hourly PM2.5 data from Delhi’s 59 monitoring stations identified 255 missing station-hour observations between 4 p.m. on November 8, the night of Deepavali, and 4 p.m. on November 9, accounting for 18% of the 1,416 expected observations,” Mr. Kumar said.He said CREA examined the implications of the missing data by replacing the 255 observations with 1,000 micrograms per cubic metre, the upper measurement limit cited by the CPCB.“With the missing peak-value data, the 24-hour average PM2.5 concentration was 269 micrograms per cubic metre. However, under the revised scenario, it increased to 400 micrograms per cubic metre, a rise of 49%. This is a conservative estimate, and the actual PM2.5 level would be even higher,” he said.