Ambient air pollution and daily mortality in ten cities of India: a causal modelling study

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About this study
This is the first multi-city study in India that examines the association between short-term exposure to PM2.5 (particulate matter <2.5 microns in size) and daily mortality during the time period 2008-2019. We analyse the impact of these short-term PM2.5 exposures across cities in various geographic regions and climatological zones of the country to generate new insights that are relevant for policy.
What did we do?
We studied this in 10 cities (Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi) between 2008 to 2019. We used a two-stage approach by first evaluating the effects of PM2.5 on mortality in each city individually, and then combining the results for all 10 cities. We also used a causal modelling approach that enabled us to isolate the effect of locally generated air pollution (such as contributions from local transport and waste burning) on mortality.
What data did we use?
We obtained daily counts of mortality from death registries of the 10 cities covered in this study for periods ranging from 3-7 years per city. Our final analysis included over 3.6 million deaths that occurred in these cities over the 2008-2019 study period. Given the sparse nature of air pollution data across many cities, we leveraged our previously developed machine-learning based exposure model that combined data from regulatory monitors, satellites, meteorology and other sources to generate PM2.5 exposure data with a high level of detail in both space (location) and time (duration).

What did we find?
We found that for every 10 μg/m3 increase in the average PM2.5 exposure over a two-day period, the daily mortality across the ten cities increased by 1.42% (Figure 1A). When using our causal modelling approach that isolated the effect of locally generated air pollution, we observed a much stronger effect on daily mortality of 3.57% (Figure 1B).
Our findings also confirmed that the risk of mortality rose more quickly at lower PM2.5 levels but plateaued as levels increased. Significantly, we found mortality risk to be very high (2.65%) even when analysing days with PM2.5 levels below the current Indian NAAQS standard of 60 μg/m3.

Figure 1: City specific estimates of the association between short-term PM2.5 and mortality per 10 μg/m3 increase using conventional time-series approach (A) and causal modelling (B).

City-specific impacts
During our study period, we found that 7.2% (95% CI: 4.2-10.1) of all deaths across all 10 cities could be linked to PM2.5 exposure surpassing the WHO guideline value of 15 μg/m3. Delhi had the highest proportion at 11.5% (equating to ~12,000 deaths per year), while Shimla had the lowest at 3.7% (59 deaths per year) between 2008-19.
Over 33,000 deaths each year were attributable to short-term PM2.5 exposures with a significant number of deaths were observed even in cities not considered to have the problem of high air pollution (column 4 in table 1 below).

Table 1: Fraction of deaths (%) and number attributable to short-term PM2.5 exposure by city

Why do cleaner cities have higher effect estimates?
In our results, we see that cities such as Bengaluru and Shimla which have relatively lower levels of air pollution showed stronger effects. This is likely due to the sharp increase in risk at lower levels of exposure which plateaus at higher levels which are unlikely to be experienced in these cities (figure 2 below).

Figure 2: Effect of short-term exposure to PM2.5 on daily mortality at lower thresholds

What is the causal modelling approach we used and what new insights does it provide?
We used an instrumental variable approach to generate causal effects of locally generated air pollution. To do this, we identified three variables or “instruments” – planetary boundary layer height or mixing height, wind speed and atmospheric pressure – that are directly related to variations in daily air pollution, but are unrelated to daily deaths except through air pollution changes. Through this approach, we isolate the effect of locally generated air pollution since these three instruments are linked to dispersal and transport of air pollution.
The results show us a much higher effect estimate of 3.57% (95% CI: 2.11-5.04), indicating that we might have previously underestimated the effect of short-term air pollution exposures on mortality. The results also highlight the need for (a) greater focus on dispersed local sources of air pollution including transport, waste burning, DG sets, etc., and (b) greater research to unpack deeper insights into the potentially compounding effects of multiple locally generated pollutants (such as PM2.5 and oxides of nitrogen).
What are the implications for national and local air pollution policy?

There are several key takeaways from this study for the development and implementation of health-focused air pollution policy across India:

1. The combination of a steep increase in risk at lower exposure levels, along with significant effects even below the NAAQS standard of 60 μg/m3, show that air pollution is a problem across the country, and even in cities otherwise considered less polluted or to have been meeting air quality standards. Remedial action to mitigate air pollution should therefore expand beyond current “non-attainment” cities.

2. The current NAAQS are substantially higher than they should be as significant effects are seen well below current guideline value for daily exposure to PM2.5 of 60 μg/m3. As the NAAQS are currently under revision, the development of appropriate health-based thresholds can be informed by integrating these results into the standard-setting exercise.

3. Focus cannot only remain on seasonal high exposure events such as during winter, requiring action on all sources year-round. Graded Response Action Plans focused solely on these extremes would only yield marginal benefits with respect to daily mortality, with negative health effects continuing to accrue all year-round even at much lower exposure levels.

4. Our causal analyses highlight the need for greater attention on the numerous dispersed sources of local air pollution across cities including from transport and waste burning among others. These are more challenging to address, but could yield substantial health benefits.
What gaps remain in our understanding?
While our study had several strengths, we also encountered challenges that lead to certain gaps in our understanding of this relationship. First, the lack of accurate information on causes of death across all cities and the lack of data on sex, age and other individual-level variables for some cities made it challenging to generate deeper insights for both policymakers and health professionals. We anticipate the need for the strengthening of health data collection and quality to facilitate the generation of these insights. Second, the lowest PM2.5 concentration observed during the entire study period across any of the cities was 17.1 μg/m3, which therefore served as the counterfactual for our analyses. Evidence from other countries has documented considerable health harms even below these levels, and those data must be considered when identifying appropriate health-based thresholds and interventions.

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Synergistic Impact of Air Pollution and Heat on Health and Economy in India


In recent years, developing countries have been grappling with two significant environmental challenges—air pollution and increasing temperature. The impact of these issues on health and the economy has been extensively studied, leading to a growing body of literature highlighting their individual consequences. Understanding the synergistic effect of air pollution and increasing temperature on human well-being is a new topic of research that has received little attention in developing nations.

This chapter, published in the book The Climate-Health-Sustainability Nexus: Understanding the Interconnected Impact on Populations and the Environment (Springer), aims to address this gap in knowledge by thoroughly examining the existing literature to understand the combined influence of these environmental stressors and their implications for global health and the economy. We look into the trends of global exposure to air pollution and temperature and explore the pathophysiological pathways through which air pollution and increasing temperature affect human health. Our findings point to a severe lack of evidence on the synergistic impact of the two on human health in India. In the face of increasing climate vulnerability, the Indian economy is exposed to large degrees of risk through direct and indirect costs. It is crucial that the interplay between air pollution and heat be studied in depth. By dissecting these pathways, policymakers and healthcare professionals can develop more targeted strategies to mitigate the combined impacts of both on public health.

Finally, we focus on the health and economic co- benefits of implementing interventions to reduce air pollution and combat heat waves. By addressing these challenges in tandem, there is an opportunity to achieve greater overall benefits for both human well-being and economic prosperity. Through a deeper understanding of these interconnected challenges, we can strive for a healthier and more sustainable future for all, especially for those most vulnerable to poor environmental quality.

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Sustainable Solutions to Crop Residue Burning and Air Pollution Cycle in India and Pakistan


Crop residue burning (CRB), or stubble burning, is common across much of India and Pakistan. Its prevalence is most highly concentrated in the agricultural belts of the Indo-Gangetic Plain (IGP) that straddles both nations. This region contributes substantially to both nations’ agricultural productivity and food security, primarily through growing staple crops, rice and wheat. While CRB occurs sporadically in different parts of both countries throughout the year, the seasonal burning occurring annually between October and November, coupled with unfavorable meteorological conditions in the IGP, results in extreme air pollution across the whole region. The byproduct of a short transition between growing seasons, the particulate matter (PM2.5) released as a result of CRB in the North-east of Pakistan and North-west of India is carried downwind to other parts of the IGP, with substantial focus afforded to the impact it has on the air quality of India’s National Capital Region due to prevailing low winds and colder temperatures. The PM2.5 levels measured in the region during this period routinely exceed World Health Organization guidelines for acceptable levels of exposure by 20-100 times, causing a public health emergency.

This chapter aims to unpack the scope of CRB across both countries, understand the proximal and distal causes, current policy interventions, and how both countries could sustainably address this issue in the long run.

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SFC Perspectives on Adaptation and Resilience, Climate Policy, Energy Transitions, and Environmental Governance and Policy


SFC Perspectives are intended to stimulate discussion by providing an overview of key issues and avenues for action to inform India’s sustainable development trajectory.

Read our Perspectives on:

1. Adaptation and Resilience: Building systems that allow India to adapt to climate impacts (by Aditya Valiathan Pillai and Tamanna Dalal)
2. Perspectives on Climate Policy: Embedding a development-centric, climate-ready approach to policymaking (by Aman Srivastava, Easwaran J Narassimhan and Navroz K Dubash)
3. Enabling the Energy Transition: Technology, politics & institutions in India’s energy system (by Ashwini K Swain, Sarada Prasanna Das, Suravee Nayak, Catherine Ayallore and Navroz K Dubash)
4. Perspectives on Environmental Governance and Policy: Systemic transformations to limit the health burden of air pollution (by Bhargav Krishna, Shibani Ghosh, Arunesh Karkun and Annanya Mahajan)

Perspectives on Environmental Governance and Policy: Systemic transformations to limit the health burden of air pollution


Air pollution is the largest risk factor for ill health in India, ahead of high blood pressure, tobacco smoking, and poor diets, contributing to ~1.7 million deaths in 2019. Home to several of the most polluted cities in the world, India has witnessed a doubling of death rates from air pollution between 1990 and 2019. The associated economic burden of this high air pollution was pegged at 1.36% of GDP or ~INR 2 lakh crores in 20191. By any metric, air pollution is a national emergency, and while some important first steps have been taken over the last few years, there is a long way to go before India achieves acceptable air quality levels.

At the Sustainable Futures Collaborative (SFC), we view reducing air pollution not only as a technical challenge, but also as a structural one that requires re-thinking our approach and the institutions that are tasked with addressing it. Systematically addressing air pollution requires a long-term, strategic, goal oriented, health-protecting framework that also integrates short-term implementable technical solutions, all executed by a capable state. Reshaping India’s air pollution policy framework to that end, we believe, will require (1) making health the basis for crafting mitigation priorities, (2) strengthening regulatory institutions in the
ecosystem, (3) executing nested, coordinated, data-driven planning and action from local to airshed levels, and (4) focusing on root causes, not symptoms.

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Impact of heatwaves on all-cause mortality in India: A comprehensive multi-city study



Heatwaves are expected to increase with climate change, posing a significant threat to population health. In India, with the world’s largest population, heatwaves occur annually but have not been comprehensively studied. Accordingly, we evaluated the association between heatwaves and all-cause mortality and quantifying the attributable mortality fraction in India.




We obtained all-cause mortality counts for ten cities in India (2008–2019) and estimated daily mean temperatures from satellite data. Our main extreme heatwave was defined as two-consecutive days with an intensity above the 97th annual percentile. We estimated city-specific heatwave associations through generalised additive Poisson regression models, and meta-analysed the associations. We reported effects as the percentage change in daily mortality, with 95% confidence intervals (CI), comparing heatwave vs non-heatwave days. We further evaluated heatwaves using different percentiles (95th, 97th, 99th) for one, two, three and five-consecutive days. We also evaluated the influence of heatwave duration, intensity and timing in the summer season on heatwave mortality, and estimated the number of heatwave-related deaths.




Among ∼ 3.6 million deaths, we observed that temperatures above 97th percentile for 2-consecutive days was associated with a 14.7 % (95 %CI, 10.3; 19.3) increase in daily mortality. Alternative heatwave definitions with higher percentiles and longer duration resulted in stronger relative risks. Furthermore, we observed stronger associations between heatwaves and mortality with higher heatwave intensity. We estimated that around 1116 deaths annually (95 %CI, 861; 1361) were attributed to heatwaves. Shorter and less intense definitions of heatwaves resulted in a higher estimated burden of heatwave-related deaths.




We found strong evidence of heatwave impacts on daily mortality. Longer and more intense heatwaves were linked to an increased mortality risk, however, resulted in a lower burden of heatwave-related deaths. Both definitions and the burden associated with each heatwave definition should be incorporated into planning and decision-making processes for policymakers.

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Media, Politics and Environment: Analyzing Experiences from Europe and Asia


Environmental protection has not equally established itself as a permanent fixture in the political systems of all countries: to date, governments and entire societies have responded to environmental challenges in a variety of ways, and concrete environmental policy is still a highly national matter. Moreover, the perception of environmental problems varies considerably on a global scale. The reasons normally cited for these differences largely stem from the environmental policy debates themselves, e.g. poverty, ignorance, capital interests, etc. In contrast, this book shows that concrete environmental policy emerges from a complex interplay of mass media and political conflicts: first, the mass media provide the framework for national environmental policy through agenda-setting, framing and scandalization; second, the mass media thereby change values in the political and social discourse, e.g. by altering the perception of global commons and expanding the possibilities of interest articulation; and third, this can lead to political decision-making processes in which legal and other measures for environmental protection are enforced. The book systematically compares industrialized countries such as Germany and Japan with several rapidly emerging countries in South and Southeast Asia.

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State’s Commitment to Environmental Governance in India: Struggle Between Developmental Pressure and Sustainability Challenges


Over the last 50 years since environmentalism first exploded onto the world political agenda, the environment has been one of the most controversial and rapidly growing areas of public policy. The green movements in North and local grass-root movements in the South countries have elevated the debate for environmental policymaking and governance. Countries in both North and South have enacted several policies and regulations for environmental protection. However, these policies have been criticized due to their superficial protective coverage, absence of concrete measures and poor execution.

Taking these contexts in the background, this chapter has tried to examine the concept and practice of environmental governance in India. It has provided a historical overview of the environmental governance and also highlighted the challenges and opportunities in the different spheres of environmental decision making by taking some examples. Methodologically, the paper would be based on a path-dependent analysis of the environmental governance in India. This chapter argues that balance in the environment-development trade-off is necessary to meet growth objectives and the enforcement measures do not necessarily obstruct the growth. Further, more public engagement as well as creative politics are required for better environmental decision making.

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