Air Quality Monitoring Discrepancy in India
Air quality in northern India during November has been characterized by reduced visibility and respiratory discomfort. Monitoring systems currently provide differing air quality index (AQI) readings, leading to public inquiry.
Government-backed applications, such as SAFAR and SAMEER, report an upper limit of 500 on India's official AQI scale. This scale converts data from various pollutants, including PM2.5, PM10, nitrogen dioxide, sulphur dioxide, carbon monoxide, and ozone, into a single numerical value.
In contrast, private and international platforms, including IQAir and the open-source monitoring platform AQI, frequently display readings exceeding 600, with some instances surpassing 1,000 on certain days. These platforms do not impose a similar cap.
India's National Air Quality Index Structure
India's official AQI scale indicates that readings above 200 are associated with breathing discomfort for most individuals upon prolonged exposure. Values between 400 and 500 are classified as "severe," potentially impacting healthy individuals and seriously affecting those with pre-existing health conditions.
The 500 cap was established over a decade ago when the National Air Quality Index was introduced. Gufran Beig, founder director of SAFAR, stated that this threshold was initially set based on the assumption that health impacts would not significantly differ beyond this point, and to prevent public alarm. This approach results in all readings exceeding 500 being represented identically on official monitors, irrespective of actual higher concentrations.
Global Comparisons and Measurement Methods
There is no universal AQI formula globally, with countries such as the US, China, and the European Union employing their own specific pollutant thresholds. For instance, the World Health Organization (WHO) guidelines categorize PM2.5 levels exceeding 15 micrograms per cubic meter over a 24-hour period as hazardous, whereas India's threshold is 60 micrograms.
Beig emphasized that comparing India's AQI with WHO or US standards can be misleading due to variations in regional adaptability, weather patterns, and local environmental conditions.
Regarding instrumentation, the Indian pollution control board utilizes Beta Attenuation Monitors (BAMs), which measure particle mass and are calibrated to standardized metrics. Conversely, platforms like IQAir rely on sensor-based monitors, according to Abhijeet Pathak, a former scientist with India's pollution control board.
Medical professionals advise wearing masks when outdoors in affected areas.