Can Mumbai trust its official air data? An IIT scientist on what to check

Professor Sachchida Nand Tripathi, atmospheric scientist, member of the steering committee of the National Clean Air Programme (NCAP) and dean of the Kotak School of Sustainability at IIT Kanpur, explains the factors influencing Mumbai’s air pollution and the measures needed to address it.

Q. Why do private and government AQI readings differ so sharply? Answer: Several factors could contribute, and it would be premature to conclude that either network is systematically overestimating or underestimating pollution. Private monitors may capture localised hotspots near construction sites and traffic corridors, while government stations may represent different microenvironments.

Technology, calibration, maintenance and humidity can also influence readings. The AQI methodology, averaging periods, pollutants included and timestamps must be comparable. The most meaningful assessment would compare PM2.5 and PM10 concentrations over the same time intervals and using the same AQI methodology.

Q. Mumbai’s skyline is hazy despite satisfactory official readings. Why? Answer: Visibility and AQI measure different aspects of atmospheric conditions. Humidity can cause airborne particles to absorb moisture and grow, increasing light scattering and making the skyline appear hazy.