Air Pollution and Extreme Heat Together Raise Death Risk in Indian Cities: Study

A recent study by the Institute of Environmental Medicine at Karolinska Institutet has determined that high air pollution and heat in Indian cities renders individuals much more likely to die. The study, in Environment International, contrasted data for 10 major Indian cities over 11 years between 2008 and 2019. It inferred that the concurrent occurrence of all these environmental catastrophes attributes much more to the death of humans compared to when they occur separately.

India often experiences both extreme heat and poor air quality, particularly in urban areas. However, little was previously understood about how the two environmental stressors interact. This study fills an important knowledge gap by probing their combined impact on public health. Comparing daily mortality rates and environmental information, scientists could establish how level of temperature and air pollution influence mortality risk when occurring together.

The study used advanced spatiotemporal models to estimate daily amounts of exposure to ambient air pollution and temperature. Over the period of the 11-year study, approximately 3.6 million deaths in urban areas across India were analyzed. The primary pollutant that was analyzed was PM2.5, or fine particulate matter, which seeps deep into the lungs and is recognized to cause a variety of health conditions.

Few of the main outcomes of the research show a sudden rise in deaths when heat and pollution levels reach their highest levels. With an increase of 10 micrograms per cubic metre (μg/m³) in PM2.5, there is an increase of 4.6% in deaths on very hot days. Besides, this is several times the 0.8% increase in deaths on normal warm days. Moreover, the risk of death rose by 8.3% when temperatures changed from warm to extremely hot at a pollution level of 20 μg/m³. This, however, rose considerably to a rise of 64% when pollution levels exceeded the threshold of 100 μg/m³, evidently demonstrating a fatal interaction between these two stressors.

To detect these associations, the investigators used time-series analyses using generalized additive Poisson regression models. These models are widely used in environmental epidemiology to estimate short-term health impacts of exposure. Interaction terms were added to these models to examine how temperature modifies the health impact of air pollution and vice versa.

The results show that in Indian cities, which are vulnerable to both heatwaves and high levels of air pollution, the health risks are not only additive but actually multiplicative. That is, the combination of heat and pollution is far more disastrous than the combination of the two individual effects taken separately. This is a growing public health issue, particularly because climate change has gone on to further escalate the occurrence and intensity of extreme heat events across the country.

The study stresses the necessity of an overall approach that considers air quality and climate hazards urgently. Indian cities are especially vulnerable due to their high population densities and high emissions rates from vehicles, industries, and others. With global warming set to increase in intensity, this will continue to worsen unless mitigation methods are adopted.

Some of the most important measures that can be implemented to reduce this cumulative health cost include curtailing emissions from common sources of air pollution such as vehicles, the burning of fossil fuels, and manufacturing processes. These measures would not just reduce mortality from pollution but also help to manage heat-related health effects. Some other important adaptation measures can be enhancing public awareness, enhancing green cover in the urban area, and instituting comprehensive early warning systems for pollution and heat.

The findings from this study are a powerful case for the merging of air pollution control policy and policy on climate change. Intervention designers must consider the synergistic impact of environmental stressors in developing responses. Municipal level efforts are of greatest significance in light of the focal nature of heatwaves and pollution events.

In conclusion, this major Karolinska Institutet study demonstrates that the health risk of being exposed to both very high temperatures and high air pollution at the same time is significantly bigger than it has been estimated until now. As India becomes more urbanized and continues to face the impacts of a climate warming up with increasing temperatures, the need for sweeping environmental health policy grows.

Source: Environment International
Credit: Karolinska Institutet / Petter Ljungman