The Air Quality Index (AQI) has long served as a simple, public-facing tool to communicate daily air quality and the associated health risks. Standard AQI categories such as Good (0-50), Satisfactory (51-100), Moderate (101-200), Poor (201-300), and so on, are based on established scientific understanding of how pollution affects human health. Importantly, for most national AQI systems, a value of 100 represents the concentration level at which air pollution begins to pose a clear health risk, especially for sensitive populations. Values below 100 are generally considered acceptable, while values above 100 are associated with increasing levels of health concern.
Even globally, systems such as the United States EPA AQI classify:
0-50 as Good,
51-100 as Moderate,
101-150 as Unhealthy for Sensitive Groups,
151-200 as Unhealthy for Everyone,
201-300 as Very Unhealthy,
and values above 300 as Hazardous.
These categories are not arbitrary, they are rooted in decades of epidemiological evidence showing how pollution affects the lungs, heart, and overall health of people across age groups.
Recently, it has been stated that AQI values below 200 may be considered “good days.” While this may be administratively convenient, it raises several concerns.
It is true that the World Health Organization air quality guidelines serve as advisory values, and that each country is free to determine its own standards based on geography, background pollution levels, socio-economic factors, and national circumstances. However, India already ranks among the most polluted countries globally. Given this reality, loosening AQI classifications rather than strengthening them could send a confusing message to the public and to policymakers.
If, even after considering “geography, background levels, socio-economic conditions, and national circumstances,” an AQI of 200 is to be labelled as a “good day,” it becomes difficult to align this decision with the known health risks. At an AQI of 150-200, scientific evidence consistently shows that:
children
older adults
people with respiratory or heart conditions
and even healthy individuals
may experience adverse health effects.
India’s pollution sources such as significant emissions from residential combustion, rapidly increasing vehicular numbers contributing to NO2 and PM2.5, decreasing green cover due to infrastructure development, and stress on natural systems due to climate change continue to exert immense pressure on air quality. Given these challenges, it is unclear how environmental or background conditions justify broadening the AQI range upward.
Changing AQI thresholds does not reduce pollution; it only reclassifies it. Health risks at AQI 150 or 180 do not diminish simply because the category label has changed. Such adjustments risk creating a misleading impression of cleaner air, when in reality, pollution levels remain high.
For instance, the claim that the number of “good days” has risen from 110 in 2016 to 200 in 2025 appears encouraging at first glance. However, under the previous AQI system, there has actually been a rise in the number of days with PM2.5 levels between 91-120 µg/m³ — pollution levels that pose serious health risks. This indicates not improvement, but a concerning increase in days with poor air quality.
Respectfully, redefining AQI categories may unintentionally mask the real extent of pollution instead of addressing its root causes. Robust standards, transparent communication, and sincere efforts to reduce emissions are essential if we are to genuinely protect public health.