Air Quality Index and Lung Health: Why the Claim of “No Direct Correlation” Is Scientifically Unsound

On December 18, 2025, the Minister of State for Environment and Climate Change, Kirti Vardhan Singh, told the Rajya Sabha that there is “no direct correlation between higher Air Quality Index (AQI) levels and lung diseases” and that no “conclusive data” exists to establish such a link. While this statement may appear cautious or technical on the surface, it fundamentally misrepresents how public health science understands causation and risk. More importantly, it stands in direct contradiction to decades of peer-reviewed scientific research, global health authority assessments, and clinical evidence. The suggestion that poor air quality, as measured by AQI, lacks a proven connection to lung disease risks normalising exposure to polluted air and undermines urgent public health action in a country already facing a severe air pollution crisis.

Understanding What AQI Actually Measures

The Air Quality Index is not an abstract or arbitrary indicator. It is a scientifically designed tool that translates measured concentrations of known air pollutants into a scale that reflects health risk. AQI values are calculated using pollutants such as fine particulate matter (PM₂.₅), coarse particulate matter (PM₁₀), nitrogen dioxide, ozone, sulphur dioxide, and carbon monoxide. Each of these pollutants has independently been shown to damage lung tissue, impair respiratory function, and increase disease risk. When AQI levels rise, it means that people are inhaling higher concentrations of substances that medical science already recognises as harmful. Therefore, to claim that AQI has no meaningful relationship with lung disease is to ignore what AQI fundamentally represents.

The Biological Reality of Air Pollution and Lung Damage

The strongest rebuttal to the claim of “no direct correlation” lies in basic human biology. Fine particulate matter, particularly PM₂.₅, is small enough to bypass the nose and throat’s protective barriers and travel deep into the lungs. Once lodged in the alveoli, these particles induce oxidative stress, a process that damages cells and genetic material. The immune system responds by triggering inflammation, which becomes chronic with repeated exposure. Over time, this leads to airway narrowing, excessive mucus production, reduced lung elasticity, and impaired gas exchange. These biological processes are not hypothetical; they are directly observed in laboratory studies, animal models, and human clinical research. They form the pathological basis of asthma, chronic obstructive pulmonary disease (COPD), bronchitis, pulmonary fibrosis, and lung cancer.

Epidemiological Evidence Cannot Be Dismissed as “Inconclusive”

Large population studies across the world consistently show that people living in areas with higher air pollution experience higher rates of respiratory illness and premature death. Long-term cohort studies tracking thousands of individuals over decades demonstrate that increased exposure to particulate matter is associated with reduced lung function, higher hospital admissions, and increased mortality from lung disease. These studies adjust for smoking, occupation, income, and other confounding factors, yet the pollution signal remains strong. In public health, causation is established not through a single experiment but through repeated, consistent findings across populations, locations, and time. By that standard, the AQI–lung disease link is well established.

International Health Authorities Have Already Reached a Verdict

The World Health Organization and the International Agency for Research on Cancer have classified outdoor air pollution and particulate matter as carcinogenic to humans. This classification is reserved for exposures where there is sufficient evidence that they cause cancer in humans. Lung cancer is only one outcome; respiratory infections, asthma, and chronic lung diseases form a much larger burden. When global health authorities recognise polluted air as a cause of disease, claims of “no conclusive data” are not scientifically credible but politically convenient.

Disease-Specific Relationships Between High AQI and Lung Illness

The connection between AQI and lung disease is not vague or general. Asthma exacerbations rise sharply within days of AQI spikes, a pattern repeatedly observed in emergency room data. COPD patients exposed to polluted air experience more frequent flare-ups and faster decline in lung capacity. Long-term exposure to PM₂.₅ has been linked to lung cancer even among non-smokers, through pollution-induced genetic mutations. Chronic exposure has also been associated with pulmonary fibrosis, a condition involving irreversible scarring of lung tissue. These are not correlations drawn from speculation but from measurable health outcomes following changes in air quality.

Children and the Elderly Reveal the Truth Most Clearly

Children and older adults provide some of the clearest evidence of the harm caused by polluted air. Children breathe more rapidly than adults and their lungs are still developing, making them especially vulnerable to toxic exposure. Studies show that children raised in polluted environments develop smaller lungs, with deficits that may persist into adulthood. Among the elderly, increases in AQI are followed by rapid rises in hospital admissions for pneumonia, bronchitis, and respiratory failure. Public health researchers rely on such vulnerable populations because their physiological responses reveal environmental harm more clearly and quickly.

Impact of Poor Air Quality on Existing Diseases and Mental Health

Air pollution does not merely initiate new illnesses; it significantly aggravates existing health conditions, often pushing vulnerable individuals into severe or life-threatening states. People living with asthma, chronic obstructive pulmonary disease, heart disease, diabetes, and weakened immune systems experience disproportionately greater harm during periods of high AQI. Polluted air increases systemic inflammation throughout the body, placing additional stress on already compromised organs. For individuals with respiratory diseases, even short-term exposure to high particulate matter can trigger acute flare-ups, increase medication dependence, and lead to emergency hospitalisation. Similarly, cardiovascular patients face heightened risks because inhaled pollutants enter the bloodstream, contributing to blood vessel inflammation, irregular heart rhythms, and increased chances of heart attacks and strokes.

The effects of air pollution also extend beyond physical illness to mental health, an area that has gained increasing scientific attention in recent years. Fine particulate matter and toxic gases have been shown to cross the blood–brain barrier, leading to neuroinflammation and oxidative stress in brain tissue. This biological disruption is associated with higher rates of anxiety, depression, cognitive decline, and sleep disorders. Long-term exposure has been linked to an increased risk of neurodegenerative conditions such as Alzheimer’s disease and other forms of dementia. Children exposed to polluted air show higher rates of attention disorders and impaired cognitive development, while older adults experience faster cognitive decline during prolonged pollution episodes.

Air pollution further exacerbates autoimmune disorders, allergies, and metabolic diseases by chronically activating the body’s stress and immune response systems. This constant inflammatory burden weakens the body’s ability to heal and regulate itself, making disease management more difficult and reducing quality of life. Mental stress caused by living in heavily polluted environments, such as reduced outdoor activity, chronic fatigue, breathlessness, and fear of health consequences, adds an additional psychological load, creating a vicious cycle between physical illness and mental distress.

Ignoring these interconnected impacts by narrowly framing air pollution as a lung-only issue severely underestimates its true health burden. AQI is not just a measure of respiratory risk; it is an indicator of widespread physiological and neurological stress affecting nearly every system of the human body. Recognising this broader impact is essential for developing meaningful public health policies, clinical guidelines, and environmental regulations that genuinely protect population health.

Indoor Air Quality and the Clinical Perspective

The discussion on AQI often focuses on outdoor air, but indoor air quality is an extension of the same problem. People spend most of their lives indoors, where pollutants from cooking, cleaning agents, furniture, poor ventilation, and outdoor infiltration accumulate. Pulmonologists increasingly recognise indoor air quality as a modifiable risk factor for lung disease. Home air quality audits, air purification, improved ventilation, and humidity control are now routinely recommended for patients with respiratory conditions. This clinical practice itself contradicts the notion that air quality lacks a direct relationship with lung health.

The Indian Context and the Cost of Denial

In India, multiple studies have shown that increases in fine particulate matter are associated with significant rises in mortality and respiratory illness. Seasonal AQI spikes coincide with overcrowded hospitals and increased dependence on inhalers and respiratory medications. These patterns are consistent, repeatable, and predictable. When official statements deny or dilute this link, they risk delaying necessary policy interventions, weakening public awareness, and shifting responsibility away from systemic solutions.

                        It is true that lung diseases are multifactorial and that no single exposure acts in isolation. However, this does not justify claiming that there is no direct correlation between AQI and lung disease. In public health science, causation is established through converging lines of evidence, biological mechanisms, population studies, clinical observations, and real-world outcomes. By these standards, the link between air pollution, AQI, and lung disease is firmly established. High AQI is not a harmless statistic; it is a warning signal of ongoing physiological injury. Denying this reality does not protect public health, it undermines it. Clean air is not a matter of debate but a fundamental requirement for healthy lungs and a healthy society.