Understanding the Delhi’s AQI Discrepancy, Delhi's AQI at 494 vs. International Monitor's 1,600
Air Quality Index (AQI) standards differ globally, reflecting each country's unique environmental policies and health guidelines. These variations are primarily due to differences in pollutant concentration thresholds and the specific pollutants monitored.
Delhi’s AQI Discrepancy: Understanding the Numbers
On Tuesday, Delhi's air quality reached hazardous levels, with the Central Pollution Control Board (CPCB) reporting an Air Quality Index (AQI) of 494. Several monitoring stations across the city recorded the maximum value of 500, prompting the government to close schools and implement strict anti-pollution measures. However, IQAir, an international monitoring platform, reported Delhi's AQI as 1,600, leading to confusion over the discrepancy.
Why the Difference in AQI?
The measurement standards of AQI differ from country to country due to the differences in pollutant scales and thresholds. The AQI scale by India is capped at 500. Levels greater than that are termed as "severe-plus." In comparison, IQAir uses a much bigger scale and labels levels greater than 500 as "hazardous," based on the US Environmental Protection Agency's model. India also considers concentrations of PM2.5 up to 60 µg/m³ acceptable, while the World Health Organization recommends a much stricter limit of 5-10 µg/m³. These differences result in varying AQI levels reported by Indian and foreign monitors.
Monitoring Systems
CPCB monitors Delhi through 40 monitoring stations, ensuring all-round coverage and uniform reporting. In contrast, IQAir uses sparse sensors on some locations. The appropriateness and quality of these placements and equipment used could affect the AQI reported. The network of CPCB is built for Indian climatic conditions, ensuring the relevance of the data for the citizens.
Reaction to Extreme Pollution
Delhi had brought in Stage 4 of the Graded Response Action Plan (GRAP) to deal with severe pollution. Restrictions placed include a ban on BS-IV diesel vehicles, limited entry of trucks, and online classes.
Offices were operating at 50% capacity with remote work encouraged.
While both CPCB and international agencies provided significant insights, the CPCB's AQI was more reliable for the Indian context as it reflected localized pollution levels and regulations.