India’s indoor air quality crisis during winter underscores the urgent need for coordinated action. Whether addressing urban pollution from external infiltration or rural hazards from biomass combustion, solutions must be grounded in technology, education, and policy.

As winter approaches, India grapples with a surge in air pollution that impacts not only the outdoor environment but also indoor air quality (IAQ). This period, compounded by Diwali celebrations and associated fireworks, presents a critical challenge for both urban and rural communities. Understanding the dynamics of indoor air pollution and addressing its health impacts has never been more important.

The Winter Pollution Spike

India’s winter air quality deteriorates with the arrival of winter due to emissions from industrial activity, vehicle exhaust, crop burning, and the added burden of Diwali’s festival firework. These activities release a host of harmful pollutants, including particulate matter (PM10 and PM2.5), nitrogen oxides (NOx), sulfur oxides (SO2), ozone (O₃), carbon monoxide (CO), and volatile organic compounds (VOCs). While these pollutants are primarily associated with outdoor air, they infiltrate indoor spaces through doors, windows, and ventilation systems, often creating indoor pollution levels on par with outdoor conditions.

The interplay between outdoor and indoor air pollution poses serious health risks. Prolonged exposure to pollutants such as PM2.5, which penetrates deep into the lungs and bloodstream, exacerbates respiratory and cardiovascular issues. Health problems linked to poor IAQ include asthma, chronic lung disease, hypertension, atherosclerosis, heart arrhythmias, and increased susceptibility to infections. For individuals with pre-existing conditions, the risks are even more pronounced.

According to a research study from Dyson published in January 2024, the air inside homes during winter was found to be 15 per cent worse than outside. Across India, the indoor air gets 41 per cent dirtier during winters, and in Delhi, it’s even worse at 48 per cent, the research paper says, adding that in India, the most polluted time inside was between 7 am and mid-day.

Urban IAQ: Hidden Health Hazards

In urban areas, the winter months reveal unique IAQ challenges. The fine particles from outdoor pollution sources infiltrate homes, offices, and public buildings, significantly degrading air quality. Studies by The Energy and Resources Institute (TERI) highlight that even well-maintained urban office spaces often record PM10 and PM2.5 levels exceeding the World Health Organisation’s (WHO) safety standards. WHO guidelines recommend annual PM2.5 concentrations below 10 μg/m³ and daily concentrations below 25 μg/m³, yet urban indoor environments frequently surpass these thresholds during winter.

While urban buildings equipped with modern HVAC systems generally manage gaseous pollutants like NOx, SO2, and CO effectively, they are less effective in controlling particulate matter infiltration. The result is a steady increase in health risks for urban residents, particularly during periods of high outdoor pollution.

Rural IAQ: The Burden of Biomass Fuels

Rural areas face an entirely different IAQ crisis. A significant portion of the rural population relies on biomass fuels – such as firewood, crop residue, and dung – for cooking and heating. The combustion of these materials releases high levels of PM2.5, CO, SO2, and NOx, which accumulate indoors due to poor ventilation.

Women and children, who spend substantial time near cooking fires, are disproportionately affected. According to TERI’s research, indoor PM2.5 levels in rural homes often far exceed WHO standards, contributing to severe respiratory and cardiovascular health issues. Unlike urban areas, rural indoor environments also see dangerously high concentrations of gaseous pollutants, which exacerbate health risks.

Addressing Divergent Challenges

Improving IAQ in both urban and rural India requires tailored solutions. For urban areas, advancements in ventilation and air filtration technologies are critical. High-quality HVAC systems and advanced air purifiers can mitigate the impact of outdoor pollution during peak pollution periods. Increasing awareness about the importance of sealing windows and doors, especially during high-pollution episodes, can also help maintain healthier indoor environments.

In rural areas, the shift toward cleaner cooking practices is imperative. The adoption of liquefied petroleum gas (LPG) and improved biomass stoves with better ventilation systems can significantly reduce indoor pollution levels. Government programs promoting clean energy solutions, coupled with public awareness campaigns, can drive this transformation.

The Role of Climate Factors

The interplay between climatic conditions and air pollution adds complexity to the IAQ scenario. For instance, the delayed onset of La Niña and the late retreat of the monsoon have raised concerns about winter air quality in northern India. La Niña typically strengthens monsoons and disperses pollutants, but its delayed impact has heightened pollution risks this year.

Researchers at the Bengaluru-based National Institute of Advanced Sciences (NIAS) have observed links between La Niña, climate change, and air quality. Last winter, Delhi recorded its cleanest air in a decade due to favourable climatic conditions. However, with stubble burning still a significant issue and La Niña’s late arrival, pollution levels in November could spike, affecting both outdoor and indoor environments.

Toward a Comprehensive IAQ Strategy

Effective management of IAQ in India requires a multi-faceted approach combining technology, policy, and public engagement. Key measures include:

• Enhanced Building Standards: Mandating advanced HVAC and air filtration systems in urban buildings can prevent outdoor pollutants from infiltrating indoor spaces.
• Promotion of Cleaner Cooking Practices: Expanding access to LPG and improved cook-stoves in rural areas can significantly reduce indoor pollution.
• Public Awareness Campaigns: Educating communities about IAQ and its health impacts can empower individuals to adopt healthier practices, such as improved ventilation and reduced reliance on biomass fuels.
• Policy Interventions: Strengthening regulations to curb outdoor pollution sources, such as vehicle emissions and industrial pollutants, can indirectly improve IAQ.
• Research and Monitoring: Investing in real-time IAQ monitoring systems can provide valuable data to guide interventions and track progress.

India’s IAQ crisis during winter underscores the urgent need for coordinated action. Whether addressing urban pollution from external infiltration or rural hazards from biomass combustion, solutions must be grounded in technology, education, and policy. By prioritising IAQ alongside outdoor air quality, India can create healthier environments and safeguard the well-being of its population.

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