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India's air quality monitors clash: Why official data stops at 500
Millions in northern India awaken each November to ashen air, hazy skies, and a daily dilemma: which air quality reading to trust. Government-backed platforms like SAFAR and SAMEER cap their Air Quality Index (AQI) at 500-the maximum on India's official scale-while private trackers such as IQAir and open-source systems routinely report figures exceeding 600, sometimes surpassing 1,000. The discrepancy leaves residents questioning which data reflects reality-and why India's scale halts at 500.
The 500 ceiling: A decade-old compromise
India's national AQI, launched over a decade ago, treats any reading above 500 as indistinguishable. The threshold was originally set to prevent public alarm, according to Gufran Beig, founder-director of SAFAR. "It was assumed that health impacts beyond 500 would remain consistent-already at their worst," he explained. Yet this approach obscures the true severity: whether pollution registers at 501 or 900, the official index labels it identically.
Beig acknowledged that global platforms avoid such caps, leading to stark contrasts. "International organizations don't impose these limits," he said. "That's why their numbers climb much higher." The BBC has sought comment from India's Central Pollution Control Board (CPCB).
Divergent standards: WHO vs. India's thresholds
The gap extends beyond caps. The World Health Organization (WHO) deems 24-hour PM2.5 levels above 15 micrograms per cubic meter hazardous, while India's threshold sits at 60 micrograms-four times higher. Experts note that AQI formulas vary globally; the U.S., China, and E.U. each apply distinct pollutant benchmarks tailored to local conditions.
"WHO provides guidelines, but every country adapts its index based on weather, environment, and adaptability," Beig said. Comparing India's AQI directly to WHO or U.S. standards can thus be misleading.
Technology divide: BAMs vs. sensor-based monitors
India's CPCB relies on Beta Attenuation Monitors (BAMs), which physically measure particle mass with standardized calibration. In contrast, platforms like IQAir use sensor-based monitors-employing laser scattering and electrochemical methods to estimate particulate counts. These sensors, while widespread, lack government approval in India.
Abhijeet Pathak, a former CPCB scientist, highlighted the calibration challenge: "Sensors can't be recalibrated for every reading like BAMs." He joined calls from environmental scientists to modernize India's framework, unchanged since 2009. "The National Air Quality Index must evolve to include sensor data," Pathak urged, emphasizing the need to remove the 500 cap as research shows health risks worsen with rising pollution.
Calls for reform amid worsening pollution
The cap persists not because pollution plateaus at 500, but because the system was designed with a fixed ceiling. With literature confirming that health symptoms intensify as pollution climbs, experts argue the scale must reflect reality. "We can't ignore that higher exposure brings graver consequences," Beig noted.
For now, residents navigate conflicting data-government figures offering a sanitized view, while global trackers paint a grimmer picture. The debate underscores a broader question: how to balance public awareness with the risk of panic, when the air itself has long since crossed the danger line.
