Thu Nov 21 04:58:01 UTC 2024: ## Delhi Chokes on Toxic Air: Discrepancies in AQI Readings Spark Confusion

**New Delhi, India** – Delhi’s air quality plummeted to severely toxic levels on Tuesday, prompting the closure of schools and stringent measures under the Graded Response Action Plan (GRAP). While the Central Pollution Control Board (CPCB) reported an overall Air Quality Index (AQI) of 494, the international monitoring app IQAir recorded a significantly higher reading of 1600.

This discrepancy stems from differing international standards for measuring AQI. India’s AQI scale caps at 500, designating anything above as “severe-plus,” while IQAir, using a US EPA-based model, categorizes readings above 500 as “hazardous.” The difference also arises from variations in the scale used for particulate matter (PM2.5).

The CPCB utilizes a network of 40 monitoring stations across Delhi-NCR, whereas international agencies like IQAir use a separate sensor network. The exact locations and calibration of these international sensors remain unclear.

While both readings indicate dangerously polluted air, the Indian government urges citizens to rely on the CPCB’s AQI data. In response to the “severe-plus” air quality, Stage 4 of GRAP has been implemented, resulting in restrictions on vehicles, a 50% work-from-home mandate for public and private offices, and the closure or online-only operation of schools. The measures aim to mitigate the impact of the severe air pollution. The disparity in reported AQI numbers highlights the complexities and challenges of accurately monitoring and comparing air quality data across different geographical areas and using varying measurement standards.

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